feat(work): implement eraseOverlapIntervals solution for non-overlapping intervals problem

.claude/skills/campaign-issues/SKILL.md

@@ -114,7 +114,12 @@ One issue per curriculum topic; owns the problem sub-issues.
   ```
 
 `Scheduled` should come from the calendar of record — `apps/api/data/schedule.json`
-(day → topic issue) — not guessed.
+(`date → { topics: [issue, …] }`; a doubled day lists two) — not guessed.
+
+Gate problems (`gate: [...]` in the same file) must exist in the catalog before their
+Saturday, or the Worker refuses to create the review issue: create each as a
+`set:optional` problem sub-issue of its natural topic. Being named in the plan keeps it
+out of the drill pool, so it stays unseen until the gate.
 
 ## Reference tables
 

.claude/skills/problem-approach/SKILL.md

@@ -0,0 +1,149 @@
+---
+name: problem-approach
+description: Write the `## Approach` section — a Mermaid flowchart that traces the submitted solution — for every docs solution page under apps/docs/content/ that lacks one, using the repo's exact placement and node conventions. Use when asked to add/implement/fill in missing approaches, draw the approach diagram for a problem page, or when `/problem-approach` is run.
+---
+
+# Problem approach diagrams
+
+Every solution page (`apps/docs/content/(<phase>)/<topic>/<num>-<slug>.mdx`) has a
+hand-owned section before the script-owned one:
+
+```
+frontmatter → ::::warning (maybe) → ### Example N / ### Constraints
+## Approach        ← this skill (Mermaid flowchart of the code below)
+## Solution        ← bun run sync owns this; never edit inside it
+```
+
+`sync.ts` regenerates only `## Solution`, so an `## Approach` placed **before** it
+survives every re-sync; anything placed inside `## Solution` is overwritten on the
+next `work/` push.
+
+## The command: fill every missing approach
+
+1. **Find the pages** (numbered pages with no `## Approach` heading):
+
+   ```sh
+   grep -L '^## Approach' apps/docs/content/*/*.mdx
+   ```
+
+2. **For each page**, read `## Solution` and write the diagram from *that code* — the
+   one on the page, not the textbook algorithm. The reader compares diagram and code
+   line by line; the diagram is a trace, not a lecture.
+
+3. **Insert** the section between the `### Constraints:` list and `## Solution`,
+   blank-line separated on both sides:
+
+   ````md
+   - `-100 <= Node.val <= 100`
+
+   ## Approach
+
+   ```mermaid
+   flowchart TD
+     …
+   ```
+
+   ## Solution
+   ````
+
+4. **Check** each diagram by hand against the syntax rules below (the docs build does
+   not parse Mermaid — a broken diagram fails only in the browser), then run the
+   docs build once at the end and review the pages in `bun run dev`:
+
+   ```sh
+   cd apps/docs && bunx blume build --isolated && rm -rf .blume-verify
+   ```
+
+Pages with two languages (`<CodeGroup>`) get **one** diagram, traced from the
+Python version. Pages with only JavaScript trace the JavaScript.
+
+## Diagram conventions
+
+Reference page: `apps/docs/content/(array)/15-3sum.mdx`. Every existing diagram
+follows this shape:
+
+```mermaid
+flowchart TD
+  S(["threeSum(nums)"]) --> O["nums.sort() — duplicates become adjacent"]
+  O --> F{"more i in 0..n-1?"}
+  F -- no --> E(["return result"])
+  F -- yes --> D{"nums[i] == nums[i-1]?"}
+  D -- yes --> F
+  D -- no --> P["left = i+1, right = n-1, target = -nums[i]"]
+  P --> W{"left < right?"}
+  W -- no --> F
+  W -- yes --> C["current = nums[left] + nums[right]"]
+  C --> Q{"current vs target"}
+  Q -- equal --> A["append triplet, skip equal neighbours, left += 1, right -= 1"]
+  A --> W
+  Q -- "current < target" --> L["left += 1 — need a bigger sum"]
+  L --> W
+  Q -- "current > target" --> R["right -= 1 — need a smaller sum"]
+  R --> W
+```
+
+- `flowchart TD`, two-space indent, one edge per line, edges listed in execution
+  order (entry first, exits as soon as they are reachable).
+- **Entry** is a stadium holding the signature: `S(["threeSum(nums)"])`. **Every
+  exit** is a stadium: `E(["return result"])`, `R(["return true"])`.
+- **Statements** are rectangles `["…"]`, in the code's own identifiers and operators
+  (`left += 1`, `freq[n] = (freq[n] or 0) + 1`). Several trivial assignments may share
+  one node, comma-separated.
+- **Decisions** are diamonds `{"…?"}` with `-- yes -->` / `-- no -->` edges. A
+  three-way branch names the outcomes: `-- equal -->`, `-- "current < target" -->`
+  (quote an edge label whenever it holds `<`, `>`, or spaces around operators).
+- **Loops** are a decision: `for` → `{"more n in nums?"}`, `while` → the condition
+  verbatim `{"left < right?"}`. `-- no -->` goes to whatever follows the loop; the
+  body's last node edges back to the decision. `continue` is an edge back to the loop
+  decision (`D -- yes --> F` above); `break` is an edge to the node after the loop.
+- **Recursion** is a statement, not an expanded subgraph: `A["left = invertTree(root.left)"]`.
+  The base case is the first decision after entry.
+- **Classes** (design problems) use one `subgraph name["method(args)"]` per public
+  method, plus a `state["…"]` subgraph describing the fields, with `state --> method`
+  edges — see `(hash-table)/146-lru-cache.mdx`. Private helpers are named inside the
+  method nodes (`"_remove_node then _add_node — move it beside the tail"`), not drawn.
+- **Annotate the why with an em dash** inside the node, sparingly (one clause, a few
+  per diagram): `"nums.sort() — duplicates become adjacent"`, `"map = {0: 1} — the
+  empty prefix"`. The dash explains the invariant that makes the step correct — the
+  one thing the code does not say.
+- **Node ids**: one or two capitals, unique per diagram (`S I L Q C E R W A B`). Class
+  diagrams prefix per method (`G1`, `P1`).
+
+### Syntax rules (a diagram that breaks the page is worse than none)
+
+- Wrap **every** label in double quotes — brackets, parentheses, `<`, `>` and `|` in an
+  unquoted label break the parser.
+- Never put `"` inside a label; use `'` for string literals (`"s == ''?"`).
+- Never use `|` anywhere — not in node labels, not as `-->|text|` edge syntax; edge
+  labels are always `-- text -->`. Write `or` for a logical or.
+- Every id an edge references must be declared with a shape the first time it appears.
+- Balanced: each `subgraph` has an `end`; each fence opens ```` ```mermaid ```` and closes ```` ``` ````.
+
+### Code that does not run
+
+Trace it anyway — the diagram documents what was submitted — and put a `::::warning`
+callout **before** the fence naming exactly why it fails (`(array)/121-best-time-to-buy-and-sell-stock.mdx`):
+
+````md
+## Approach
+
+::::warning
+The diagram traces the code below literally. That code does not run: `curr` and `ans` are never initialised, so the first `curr > left` test raises `NameError`.
+::::
+
+```mermaid
+…
+```
+````
+
+Do not fix the code on the page: `## Solution` mirrors `work/1`, and the fix belongs
+there (then `bun run sync`).
+
+## Do not
+
+- Do not write prose approaches, complexity tables or alternative algorithms — the
+  section is one flowchart (plus the warning callout when the code is broken).
+- Do not touch `## Solution` or anything after it, nor the frontmatter `topics:` /
+  `video:` keys (`bun run sync` / `bun run videos --write` own them).
+- Do not add an approach to `reference/` pages or `index.mdx` — only numbered
+  solution pages (`title: 'NN. …'`) carry one.

.github/workflows/close-solved.yml

@@ -7,7 +7,7 @@ on:
   workflow_dispatch:
     inputs:
       dry_run:
-        description: Report matches without closing anything
+        description: Report matches and would-be releases without closing or releasing anything
         type: boolean
         default: false
 
@@ -61,3 +61,39 @@ jobs:
             exit 0
           fi
           bun apps/cli/sync-project-fields.ts
+
+  # One timever release per finished topic (every core sub-issue closed),
+  # tagged at the instant the last core problem closed. It reads the same rule
+  # close-topics uses (apps/cli/topics.ts) straight off the sub-issues, so the
+  # push that finishes a topic releases it in this run — no waiting for Close
+  # Topics, which chains after this workflow. Reconciling: a run releases
+  # every finished topic still missing one, so a manual dispatch backfills and
+  # a problem closed by hand in the UI is picked up by the next run.
+  release:
+    needs: close
+    # Like close-topics: a partially failed close still closed some issues,
+    # and the script only reads state, so run unless the run was cancelled.
+    if: ${{ !cancelled() }}
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write # push tags, create releases
+      issues: read
+    steps:
+      # Full history: each tag targets the last main commit before its topic
+      # finished, and backfilled tags reach far behind HEAD.
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - uses: oven-sh/setup-bun@v2
+
+      # The tagger of the annotated, backdated tags.
+      - run: |
+          git config user.name "github-actions[bot]"
+          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
+
+      # No install step: the script only uses Bun builtins + fetch.
+      - run: bun apps/cli/release-topics.ts
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          DRY_RUN: ${{ inputs.dry_run }}

.github/workflows/deploy.yml

@@ -30,7 +30,13 @@ jobs:
       - uses: oven-sh/setup-bun@v2 # skip if you use npm/pnpm
 
       - run: bun install --frozen-lockfile
+      # blume.config.ts pulls the /changelog pages from this repo's GitHub
+      # releases (githubReleases source) at build time. The token authenticates
+      # that fetch — required if the repo is private, and it lifts the shared
+      # runner's unauthenticated API rate limit. `contents: read` covers it.
       - run: bun run build
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
       - uses: actions/upload-pages-artifact@v3
         with:
@@ -48,8 +54,9 @@ jobs:
 
   # Deploys on every main push (not path-filtered): apps/api/data/schedule.json
   # is bundled at deploy time, and re-deploying an unchanged Worker is a no-op.
-  # Needs repo secrets CLOUDFLARE_API_TOKEN (Workers Scripts: Edit) and
-  # CLOUDFLARE_ACCOUNT_ID.
+  # Needs repo secrets CLOUDFLARE_API_TOKEN (Workers Scripts: Edit),
+  # CLOUDFLARE_ACCOUNT_ID, and OPENROUTER_API_KEY (the docs assistant's
+  # POST /ask; the Actions secret is the one copy, mirrored into the Worker).
   deploy-api:
     runs-on: ubuntu-latest
     steps:
@@ -62,6 +69,13 @@ jobs:
       # DST cron guards must hold before the Worker ships.
       - run: bun run api:test
 
+      - run: printf %s "$OPENROUTER_API_KEY" | bunx wrangler secret put OPENROUTER_API_KEY
+        working-directory: apps/api
+        env:
+          CLOUDFLARE_API_TOKEN: ${{ secrets.CLOUDFLARE_API_TOKEN }}
+          CLOUDFLARE_ACCOUNT_ID: ${{ secrets.CLOUDFLARE_ACCOUNT_ID }}
+          OPENROUTER_API_KEY: ${{ secrets.OPENROUTER_API_KEY }}
+
       - run: bun run api:deploy
         env:
           CLOUDFLARE_API_TOKEN: ${{ secrets.CLOUDFLARE_API_TOKEN }}

.gitignore

@@ -1,5 +1,6 @@
 # dependencies (bun install)
 node_modules
+.openlogs
 tmp/
 *.log
 .crush

AGENTS.md

@@ -14,6 +14,7 @@ flowchart LR
   work -->|close-solved.yml| PI[problem issues]
   work -->|close-solved.yml POST /admin/solved| D1[(D1 = SRS state)]
   PI -->|close-topics.yml| TI[topic issues]
+  PI -->|close-solved.yml release job| Rel[timever release per finished topic]
   GH[GitHub issues = catalog] -->|nightly reconcile| D1
   D1 -->|8 AM ET cron| Mail[digest email + one-tap links]
   Mail -->|GET /log| D1
@@ -23,6 +24,7 @@ flowchart LR
   D1 -->|Sat midnight ET| Review[Review — Week N issue]
   PI -->|"spaced-repetition.yml (6 AM ET cron, closed +3d/+7d)"| SR[Spaced Repetition — Month D issue]
   D1 --> Charts[SVG charts + /api/stats]
+  Charts -->|bun run stats| TUI[terminal dashboard]
 ```
 
 - **Reconcile, don't react.** `close-solved.ts`, `close-topics.ts`, and the Worker's catalog sync recompute desired state from scratch each run: re-runs are no-ops, backfills need no special casing, closing is one-directional. `close-solved` posts its *whole* implemented set to `/admin/solved`, not just the issues it closed this run.
@@ -32,9 +34,11 @@ flowchart LR
 - **The picker owns the local review loop; the buckets are its state.** `work/` holds three buckets (`1` = first solve, `3`/`7` = blind re-solves, named after the ladder rungs) and `bun run pick` has three sections — Tab cycles them. Pools are reconciled from the filesystem plus one `git log` (`apps/cli/work.ts`): a first solve dates from the ET date of the commit that added its `work/1` file — the same push that closes the problem issue and starts the +3/+7 windows — and a window stops being owed the moment its bucket holds a file. Uncapped, unlike the review issue's `WINDOW_CAP`: that issue is one day's assignment, the picker is everything still owed. An empty scaffold under `work/1` owes nothing (it is unsolved), which is why `isImplemented()` lives in `apps/cli/source.ts` and is shared with `close-solved.ts`. leetcode-cli reads its output directory from `~/.leetcode/workspaces/<active>/config.json` and nowhere else — no flag, no env var — so `pick.ts` MERGES `workDir` into that file around the child (never replays saved bytes: the CLI owns the file too) and leaves it pointed at `work/1`, then treats the scaffold's existence as the acceptance test, since leetcode-cli exits 0 even when an expired session made it write nothing. The picker itself writes no state: pushing the re-solve is what moves the ladder, via `close-solved` → `/admin/solved` with that file's bucket.
 - **The README charts are live, never committed.** They are Worker endpoints reading D1 per request (`Cache-Control: max-age=300`, honored by GitHub Camo), so a solved push moves them within ~5 minutes with no commit and no workflow of their own.
 - **D1 owns SRS state; GitHub issues own the catalog; `apps/api/data/schedule.json` owns the calendar.** The catalog reconcile never invents rows and never overwrites SRS columns (`stage`, `next_review`). `Target Date` is the *only* Project field the Worker mirrors (`apps/api/src/mirror.ts`): failures are warnings, never lost D1 writes; topic rows' `Target Date` is never written. SRS stage and first-attempt result live **only** in D1 — do not re-add them as Project fields. The Project's `Set`/`Difficulty` single-selects are a projection of the issue labels, reconciled by `bun run sync-project-fields` — a best-effort final step of `close-solved.yml`, never the Worker.
+- **The plan names days; the samplers fill the gaps.** `apps/api/data/schedule.json` maps a date to a `ScheduledDay` (`apps/api/src/srs.ts`): `topics` (one or more topic issues — a doubled day lists two, and the digest renders each with its core list then the optional "if time" list), `problems` (a set day: fixed numbers, rendered like a topic), `gate` (Saturday's blind set, verbatim — `createReviewIssue` refuses to create the issue if any number is not a catalog row, so gate problems must exist as `set:optional` sub-issues of their topic first), or `sweep` (every problem whose last attempt failed, taps to re-log, no drills). Every number a `gate` or `problems` entry names is in `RESERVED`, and the drill/gate samplers never draw it — that is what keeps a planned gate problem unseen until its Saturday. Dates absent from the plan still get the ladder's reviews and drills; a Saturday without a `gate` entry falls back to sampling this week's optional pools.
 - **Determinism = idempotency.** Drill/gate sampling uses a seeded PRNG (`rng()` in `apps/api/src/srs.ts`, FNV-1a → mulberry32, seed = date / ISO week); the digest is keyed by ET date in `email_log`; one-tap links are unique on (problem, date, kind).
 - **DST-proof crons:** each event has two UTC crons; code fires only on the computed ET hour (`etHour`), unit-checked in `apps/api/src/srs.test.ts`.
 - **Chained workflows:** `GITHUB_TOKEN`-driven issue closes fire no `issues` events, so `close-topics.yml` chains off `workflow_run` of Close Solved instead. The Worker's webhook uses its own `GH_PAT`, so its events flow normally.
+- **One "finished topic" rule, two consumers.** `apps/cli/topics.ts` (`coreSet()`: every `set:core` sub-issue closed, zero core = never) is read by `close-topics.ts` (closes the topic issue) and `release-topics.ts` (the `release` job of `close-solved.yml`). The release reads the sub-issues, not the topic issue, so the push that finishes a topic releases it in the same run instead of waiting for Close Topics to chain after it. Version = [timever](https://gist.github.com/twolfson/de1b004dd22536b8e668) (`YYYYMMDD.HHMMSS.NNNNNNNNN`, UTC) of the instant the last core problem closed; the tag is annotated and backdated to that instant, on the last first-parent main commit before it; the body is a changelog snapshot at that instant (a one-sentence summary first — Blume's changelog makes it the page's meta description — then closed on the finish day / earlier / open at release, with solution links at the tag). A release is found by its `<!-- release-topics: #N -->` body marker, never by tag name, so re-closing a core problem never mints a second one; an existing release keeps its tag and has its name (the topic title) and body rewritten whenever the render changes. The docs `/changelog` is these releases (`githubReleases` in `apps/docs/blume.config.ts`, fetched at build with `GITHUB_TOKEN`), dated by the timever tag, not `published_at` (which the API cannot backdate): `releasesDatedByTag` rewrites each timever release's `published_at` before Blume maps it, via `custom(githubReleasesSource(…))` because the config-level `githubReleases()` takes no `fetchImpl`. Changing the tag format breaks the changelog dates.
 
 ## Key Directories
 
@@ -42,9 +46,10 @@ flowchart LR
 |---|---|
 | `work/<1\|3\|7>/<Difficulty>/<Category>/<num>.<slug>.{js,py}` | Solutions, e.g. `work/1/Easy/Array/1.two-sum.py`. The top directory is the spaced-repetition bucket: `1` = first solve, `3`/`7` = the blind re-solves of that problem 3 and 7 days later. Machine-parsed header comment (title / `Difficulty:` / URL / `─` rule / statement) — preserve its exact shape |
 | `apps/cli/` | Flat Bun TS workspace: automation entries (shebang + top-level await) and libraries (no shebang, side-effect-free on import). Root `bun run` scripts delegate here |
-| `apps/docs/` | Blume site (`blume.config.ts`, `content/`, `islands/`, `public/`). `content/(<category>)/<num>-<slug>.mdx` generated by sync |
-| `apps/api/` | Cloudflare Worker workspace: `src/` modules, `data/schedule.json` (day → topic issue, human-edited, bundled at deploy), `migrations/` (append-only; `0002` is the +3/+7 ladder rebuild) |
-| `.github/workflows/` | deploy (docs → Pages, Worker → Cloudflare, on every main push), close-solved (issues + `/admin/solved` + Project `Set`/`Difficulty`, needs `SRS_ADMIN_KEY` and `PROJECT_PAT`), close-topics, sync-d1 (issue edits → `/admin/reconcile`), spaced-repetition (daily 06:00 ET cron → today's review issue; `GITHUB_TOKEN` only, no secrets) |
+| `apps/docs/` | Blume site (`blume.config.ts`, `content/`, `components/` + `components.ts`, `islands/`, `public/`). `content/(0N-<phase>)/<topic>/<num>-<slug>.mdx` plus one `meta.ts` per phase and per topic folder, all generated by sync (a phase's once, then hand-owned): the phase folder is a `(group)` (sidebar section, no route segment), the topic folder is the README campaign topic slug (`tree-dfs/`, `heap-priority-queue/`) and a real route segment (`/tree-dfs/invert-binary-tree`), the `meta.ts` files carry the exact labels, phase/topic numbers and icons so the sidebar reads in curriculum order with each topic a collapsible group. A problem page's badge row (between the description and the body) is rendered, not written: the MDX `wrapper` (`components/ProblemBadges.astro`, registered as `mdx.wrapper` in `components.ts` — Blume's page template renders the title and description itself with no slot before the body, so the wrapper, which MDX hands no route, reads it off `Astro.url`) reads the page's `topics:` (LeetCode's topic tags, from sync) and `video:` (NeetCode YouTube id, from `bun run videos`) frontmatter — both declared via `frontmatter.extend` in `blume.config.ts`, hand-rolled Standard Schemas, no zod — and links a tag the campaign teaches to its topic landing page (filled), any other tag to its guide page `/guides/<slug>` (outlined; LeetCode's problem list if the guide is gone, gray and iconless), and the video as a red `Explanation` badge. Every badge in the row is a pill. A tag badge carries the icon its target shows in the sidebar (read off `data.navigation`: the topic `meta.ts` icon, the guide's `icon:`) and the tag's own colour from `lib/tag-colors.ts` — unique per tag site-wide, assigned greedily over every tag with a page so tags that share problem pages sit furthest apart in OKLab, in a lightness band that keeps ≥ 3:1 contrast in both themes (Blume's Badge takes one hex for both). The reverse direction is the `PageFooter` slot (`components/BacklinksList.astro`): an Obsidian-style `<num> <name>` list under every topic landing and guide page of the problems whose badges link there, plus a topic's own folder members (so a topic no tag names, `hybrid-structures`, still lists its problems), in a native `<details>` open on load whose top-right chevron collapses it (no JS); problem pages are recognised by their `<num>. <name>` title and render no list. Which tags the campaign teaches is ONE map, `apps/docs/topic-landings.ts` (tag slug → landing routes), and where a badge points is ONE function beside it, `tagTarget()` — read by both components (so badges and backlinks cannot disagree) and the map by sync. `content/guides/` (the `Guides` header tab) is one page per tag outside that map, filed by hand into `(group)` categories — `(1-data-structures)/`, `(2-algorithms)/`, `(3-techniques)/` (hand-written `meta.ts` each; no route segment, so every guide stays `/guides/<slug>`). Sync finds a guide by slug anywhere under `guides/` and creates a placeholder only when none exists or it is empty — at the `guides/` root, for you to file into a category and give a Lucide `icon:` — the one every badge linking to it shows — that no topic and no other guide uses (sync warns while it is missing, a `TOPIC_ICONS` value, or another guide's) — and after that owns exactly one key of it: `sidebar.badge`, the sidebar count, rewritten every run to the guide's backlink count (problem pages carrying the tag — equal to the `BacklinksList` rows, since a guide's tag has no landing; dropped at zero). Everything else is hand-owned (a guide whose tag no page carries any more is left alone, badge dropped), with frontmatter `list:` — the tag's LeetCode problem list, rendered by the same wrapper as an orange `LeetCode list` badge; sync also writes `guides/meta.ts`. A hand-written `(0N-<phase>)/<topic>/index.mdx` (`hidden: true`) is that topic's landing page: Blume ≥ 1.7.3 links the sidebar group row to it (`sliding-window/index.mdx` → `/sliding-window`) and the hidden flag drops the duplicate row. Two kinds of custom MDX component, both import-free on every page: `islands/<Name>.tsx` is hydrated React (auto-discovered; the five `/progress` cards `SolvedRing`/`SubmissionHeatmap`/`SubmissionChart`/`TopicBubbles`/`RecentSolves`, and `DependencySpine` — the README topic map as data, zoom/pan, nodes link to whatever route Blume's `/api/docs/navigation.json` reports for the topic folder, inert until a topic has pages), `components/<Name>.astro` registered in `components.ts` is static markup plus a custom element for behaviour, the way Blume's own `Frame` is built (`Carousel`/`CarouselImage`: `src` takes a URL, `/file.png`, or the page-relative `../../public/file.png`) |
+| `apps/api/` | Cloudflare Worker workspace: `src/` modules, `data/schedule.json` (the plan: `date → { topics | problems | gate | sweep }`, human-edited, bundled at deploy), `migrations/` (append-only; `0002` is the +3/+7 ladder rebuild) |
+| `.github/workflows/` | deploy (docs → Pages with `GITHUB_TOKEN` for the releases-backed changelog, Worker → Cloudflare with the `OPENROUTER_API_KEY` Actions secret put into it first, on every main push), close-solved (issues + `/admin/solved` + Project `Set`/`Difficulty`, needs `SRS_ADMIN_KEY` and `PROJECT_PAT`; then the `release` job: timever tag + release per finished topic, `contents: write`), close-topics, sync-d1 (issue edits → `/admin/reconcile`), spaced-repetition (daily 06:00 ET cron → today's review issue; `GITHUB_TOKEN` only, no secrets) |
+| `.githooks/` | Tracked git hooks; `bun install` points `core.hooksPath` here (root `prepare` script, no husky). `pre-commit` runs `bun run sync` and stages only what sync changed (pages, `apps/docs/redirects.ts`), so a solution, its page and its `/<num>` short link land in one commit; it refuses to run while `work/1` has anything unstaged (sync reads the tree, so the page would not match the commit), and leaves pre-existing dirt under `apps/docs/content` (in-progress `## Approach` prose) unstaged. `git commit --no-verify` for a deliberate partial commit |
 
 ## Development Commands
 
@@ -56,14 +61,23 @@ bun run pick            # scaffold a solution via leetcode-cli (fuzzy picker; Ta
                         # re-solves → work/3, work/7. Each section hides what its own bucket
                         # already holds; index+descriptions cached in
                         # ~/.local/share/leetcode/data.db — see apps/cli/db.ts)
+bun run stats           # terminal dashboard over GET /api/stats — four panes (Overview,
+                        # Ladder, Concepts, Activity); Tab/1-4 switches, ↑↓ scrolls,
+                        # r refetches, q quits. Outside a TTY it prints every pane once.
+                        # SRS_API points it at a local Worker like close-solved does.
 bun run test            # run ONE solution against LeetCode's judge (not a test suite;
                         # most recently tested first, stamped in the db on exit 0)
 bun run submit          # submit ONE solution to LeetCode (newest scaffold first, nothing
                         # hidden; last_submitted stamped in the db on exit 0)
-bun run sync            # work/1 → apps/docs/content/ pages (re-solves are never published)
+bun run sync            # work/1 → apps/docs/content/ pages + apps/docs/redirects.ts (/<num> short
+                        # links; re-solves are never published)
+bun run videos          # docs pages with no `video:` frontmatter → NeetCode video per page
+                        # (channel search scraped, no API key; --write adds the
+                        # `video:` key; "no NeetCode match" pages stay untouched)
 bun run dev|build       # Blume docs site (runs in apps/docs/)
 bun run close-solved -- --dry-run    # issue reconcilers (also DRY_RUN=1)
 bun run close-topics -- --dry-run
+bun run release-topics -- --dry-run # prints every would-be topic release body
 # close-solved also pushes the solved set to the Worker; point it at a local
 # one and nothing production is touched:
 SRS_API=http://localhost:8787 SRS_ADMIN_KEY=$LINK_KEY bun run close-solved -- --dry-run
@@ -92,21 +106,22 @@ curl -X POST -H "Authorization: Bearer $LINK_KEY" \
 
 ## Important Files
 
-- `apps/api/src/srs.ts` — SRS domain: the ladder (`new → +3 → +7 → retired`; fail resets to `+3`; first-ever log enters at `+3`), `WINDOWS`/`STAGES` (the one vocabulary shared by the charts, the `work/<n>` buckets and the review issues), ET date math, `workingDay()` (no scheduled date is ever a Sunday), seeded sampling, `logAttempt()` (the ONE write path — email taps, webhook, gate scoring all converge here), and overload leveling: at most `REVIEW_CAP` (3) reviews surface per day — `levelReviews()` (run by `sendDigest` on real sends only, never dry) gives everything past the cap a concrete future WORKING day, ≤ 3 per day, oldest first, instead of letting the due pile grow.
-- `apps/api/src/index.ts` — router + cron dispatch; `apps/api/wrangler.jsonc` — bindings (`DB`, `EMAIL`), crons, vars; secrets `GH_PAT`/`WEBHOOK_SECRET`/`LINK_KEY` via `wrangler secret put`.
+- `apps/api/src/srs.ts` — SRS domain: the ladder (`new → +3 → +7 → retired`; fail resets to `+3`; first-ever log enters at `+3`), `WINDOWS`/`STAGES`/`TEMPERATURES`/`DIFFICULTIES`/`SETS` (the one vocabulary shared by the charts, the `work/<n>` buckets, the review issues and the stats dashboard), ET date math, `workingDay()` (no scheduled date is ever a Sunday), `temperatureOf()` (days since a concept was last exercised → `hot`/`fresh`/`fading`/`cold`, bands derived from `WINDOWS` so they cannot drift; read-side only, nothing is scheduled off it), seeded sampling, `logAttempt()` (the ONE write path — email taps, webhook, gate scoring all converge here), and overload leveling: at most `REVIEW_CAP` (3) reviews surface per day — `levelReviews()` (run by `sendDigest` on real sends only, never dry) gives everything past the cap a concrete future WORKING day, ≤ 3 per day, oldest first, instead of letting the due pile grow.
+- `apps/api/src/index.ts` — router + cron dispatch; `apps/api/wrangler.jsonc` — bindings (`DB`, `EMAIL`), crons, vars; secrets `GH_PAT`/`WEBHOOK_SECRET`/`LINK_KEY` via `wrangler secret put`, and `OPENROUTER_API_KEY`, whose one copy is the repo's Actions secret (deploy.yml puts it before every deploy — rotate it there).
+- `apps/api/src/ask.ts` — `POST /ask`, the docs assistant's backend. Blume's own assistant route is server-rendered and cannot ship in the static Pages build (`BLUME_SERVER_FEATURE_REQUIRED`), so `blume.config.ts` sets `ai.assistant.endpoint` to this route instead of a `provider`. It speaks the Blume island's wire contract (`{ messages, page: { path } }` in, a plain-text stream out, a 503 "The assistant is not configured…" when the key is missing), validates like Blume's generated route (1–40 user/assistant messages, 24 000 chars, 64 KB — no caller system prompt), grounds on the published `llms-full.txt` (current page first, then keyword-ranked excerpts in Blume's 6 × 2 000 / 10 000-char budget, cached 5 min), and streams OpenRouter's chat completions over plain `fetch` — no AI SDK — for the `ASK_MODEL` var. `:free` models share an upstream pool and often answer 429, which the island shows as its rate-limit notice.
 - `apps/api/src/digest.ts` / `apps/api/src/email.tsx` — the daily digest, split data/presentation. `digest.ts` reads D1 into a `DigestData`; `email.tsx` owns every colour and every sentence, and renders both the HTML and (via its own `plainDigest`, not React Email's `plainText` mode, which flattens the tables) the text alternative. The retrieval rules hold by construction: `DigestRow` has no title and no issue field, so a review or drill line *cannot* leak the topic or a solution link. Subject is `(Day N/56) LeetCode Daily Digest`.
 - `apps/api/src/png.ts` — hand-rolled PNG encoder (RGB8, one IDAT, zlib via `CompressionStream("deflate")`, CRC32, 5×7 bitmap font). It exists because every major email client refuses remote SVG, so `/chart/heatmap.png` rasters the heatmap for the digest while `/chart/heatmap.svg` keeps serving the README byte-for-byte. Both come from one `heatmapCells()` so the two pictures cannot drift.
-- `apps/cli/sync.ts` — work→docs contract: only `## Solution` onward is script-owned on existing pages; human prose is never touched; never hand-write solution pages or edit inside `## Solution`.
-- `apps/cli/work.ts` — the `work/` layout: bucket paths, `firstSolved()` (one `git log`, ET dates, keyed by LC number so past layout moves don't matter), and `reviewQueues()` (what each window still owes). Everything that needs to know where a solution file lives, or when it was solved, goes through here.
-- `README.md` live charts are Worker endpoints (`/chart/*.svg`, `/badge/gate.svg`, 5-min Camo cache); the docs `/progress` page fetches `/api/stats` client-side (`apps/docs/islands/ProgressDashboard.tsx`).
-- `apps/docs/blume.config.ts` — site base `/leetcode`; `README.md` campaign table doubles as topic-map input to `sync.ts` (`readmeTopics()`, `TOPIC_ALIASES`).
+- `apps/cli/sync.ts` — work→docs contract: on existing pages only the frontmatter `icon:` and the `## Solution` section are regenerated, and `topics:` (LeetCode's `topicTags` as `{ name, slug }`, fetched by GraphQL) is filled once — on create, or on any run that finds it missing — never refreshed (delete the key to refetch; offline, the page is written without it and the next sync retries). `## Solution` is the latter bounded by `solutionEnd()` at the next unfenced top-level heading; human prose before it and any sections after it are never touched. Never hand-write solution pages or edit inside `## Solution`. Two classifications, two homes: the sidebar group is the README topic (`readmeTopics()`, first listing wins for a problem under two topics; a warm-up outside the plan groups under its category at `order: 0`, ahead of topic 1) and the `work/1/<Difficulty>/<Category>/` category, which only places an unplanned problem — the page's topic badges are LeetCode's tags, not either classification. Topics nest under their README phase (`## Phase N — Name` headings, shortened via `PHASE_ALIASES`): `content/(0N-<phase>)/<topic>/`. The topic `meta.ts` is script-owned and rewritten every run (label, curriculum order, `TOPIC_ICONS` icon, `display: "group"`); the phase `meta.ts` is written once when missing (`Phase N: Name`, `order: N`) and hand-owned after — rename its title freely. Never rewriting it loses nothing: its order and name are also the folder name, so a README change to either lands in a new folder with a fresh meta. The phase folder is a Blume `(group)` — no route segment, so `/tree-dfs` is unchanged and a landing page there is one level deep, never at `/` — and the topic folder is the real segment; never put a topic `index.mdx` directly inside a `(group)`. A page is `rename`d when its topic or phase changes; a folder every page has left is deleted (climbing into an emptied phase folder) unless it still holds a hand-written `index.mdx` (sync never writes, moves, or deletes one — so page-relative asset paths in a moved landing page are yours to fix). Slugs come from `slugify()`, which glues a leading number to the next token (`1d-dynamic-programming`) because Blume strips `<digits>-` prefixes from routes. The hand-owned parts have their own owners: `## Approach` (a Mermaid flowchart tracing the page's code, placed *before* `## Solution` so a re-sync keeps it) is written per the `problem-approach` skill (`/problem-approach` fills every page missing one); the frontmatter `video:` (the NeetCode walkthrough, rendered as the red `Explanation` badge) is added by `bun run videos --write` (`apps/cli/videos.ts`).
+- `apps/cli/work.ts` — the `work/` layout: bucket paths, `isSolution()`/`solvedInBucket()` (the stub test, shared with `close-solved.ts`), `firstSolved()` (one `git log`, ET dates, keyed by LC number so past layout moves don't matter), and `reviewQueues()` (what each window still owes). Everything that needs to know where a solution file lives, or when it was solved, goes through here.
+- `apps/api/src/stats.ts` / `apps/cli/stats.ts` / `apps/cli/tui.ts` / `apps/cli/api.ts` / `apps/docs/lib/stats.ts` — the read side. `buildStats()` is the ONE aggregation: phases, ladder, difficulty, `attempting` (open misses, via `MISS_WHERE` in `srs.ts` — the sweep day's definition), per-topic temperature, gates, the 14-day due queue, `heat` (every campaign day, zeros and future days included — the TUI windows its tail rather than asking a second question), `recent` (the ten problems most recently solved, dated by each one's first pass) and `year` (the 365 days ending today — always the calendar year to date — each split by difficulty into attempts and first solves; the docs cards window and bucket it themselves). Two readers consume it, the docs `/progress` islands and `bun run stats`, so its shape is their contract: change the Worker and both readers together (additive fields a reader ignores are safe). `tui.ts` is hand-rolled ANSI (bars, sparklines, heat cells, alternate screen) on charts.ts's palette, and every chart differs by GLYPH as well as by colour so a piped or `NO_COLOR` dashboard still reads. The TUI recomputes nothing: the only local fact it shows is the `work/` solution count, which is inventory, not schedule.
+- `README.md` live charts are Worker endpoints (`/chart/*.svg`, `/badge/gate.svg`, 5-min Camo cache). The docs `/progress` page is five LeetCode-style islands — `SolvedRing` (difficulty gauge + "Attempting"), `SubmissionHeatmap` and `SubmissionChart` sharing one row (the heatmap: the last six months in month blocks, the README's colour ramp as theme.css `--heat-0..4`, its attempts / active days / max streak counted from the cells it draws; the chart: this calendar year as stacked Easy/Med./Hard bars per month or week, first solves or every attempt, via two shadcn `ToggleGroup`s), `TopicBubbles` (the campaign topics circle-packed by `d3-hierarchy`, filled by solved share), `RecentSolves` (the ten most recent, linked through `redirects.ts`) — composed from shadcn/ui (`components/ui/{card,chart,skeleton,toggle,toggle-group}.tsx`, Recharts under `chart`, Radix under the toggles) on Blume's tokens: `apps/docs/theme.css` maps shadcn's names onto `--blume-*` (never `accent`, which is Blume's brand colour — vendored components that use it, like `toggle.tsx`, are retokened to `background`/`muted`) and gives shadcn's `data-slot` parts their border colour. They share `lib/stats.ts` (`useStats()`), so the page makes ONE `/api/stats` request however many islands hydrate. shadcn sources live outside `islands/` (every `.tsx` there becomes an island) and import `lib/utils` relatively — Blume's Vite has no `@/` alias; `components.json` + `tsconfig.json` exist for the shadcn CLI and `tsc`, so after `shadcn add` rewrite `@/…` imports to relative ones — and check `package.json`: the CLI has twice installed an unrelated `cn` package for `lib/utils` and skipped real deps (`class-variance-authority`). Blume's `.prose :where(a, p, ol)` rules ignore `not-prose`, so island markup overrides them with `!` utilities, as Blume's own components do.
+- `apps/docs/blume.config.ts` — site base `/leetcode`; imports `apps/docs/redirects.ts`, sync-generated (`/<num>` → `/<topic>/<slug>`, one row per page, exact root-relative paths — Blume adds the base and, for the static Pages build, emits a meta-refresh page per rule plus `blume-redirects.json`); `README.md` campaign table doubles as topic-map input to `sync.ts` (`readmeTopics()`, `TOPIC_ALIASES`, `PHASE_ALIASES`).
 - Old `.github/srs/` JSON state, its `srs-*` Actions, and the one-shot `import-srs.ts` importer are RETIRED and deleted — do not resurrect; git history is the record.
 
 ## Runtime/Tooling Preferences
 
 - **Bun only**: run scripts with `bun apps/cli/<name>.ts` (or the root `bun run` aliases), install with `bun install --frozen-lockfile`. One workspace (`apps/*`), one root `bun.lock`. Node 22 appears only in `deploy.yml` because Blume requires it.
-- **No root tsconfig, no ESLint, no Prettier** — match surrounding style by hand. `apps/api/` has a strict `tsconfig.json`; `Env` types are generated (`bunx wrangler types`), never hand-written.
-- **Near-zero runtime npm dependencies** — SVG, PNG, HMAC (WebCrypto), GraphQL are hand-rolled; Actions scripts use Bun builtins + `fetch` only. The **one** exception is the digest email: `apps/api/src/email.tsx` renders React Email (`react`, `react-dom`, `@react-email/components`, `@react-email/render`) inside the Worker, because hand-rolling table-based email HTML that survives Gmail *and* Outlook is not worth owning. It costs ~235 KB gzipped of a 3 MB budget, needs no `nodejs_compat` (it resolves to `renderToReadableStream`), and requires `"jsx": "react-jsx"` in `apps/api/tsconfig.json`. Do not extend this exception to any other module.
+- **Near-zero runtime npm dependencies** — SVG, PNG, terminal ANSI, HMAC (WebCrypto), GraphQL are hand-rolled; Actions scripts use Bun builtins + `fetch` only. Two exceptions, each confined to one surface. The digest email: `apps/api/src/email.tsx` renders React Email (`react`, `react-dom`, `@react-email/components`, `@react-email/render`) inside the Worker, because hand-rolling table-based email HTML that survives Gmail *and* Outlook is not worth owning. It costs ~235 KB gzipped of a 3 MB budget, needs no `nodejs_compat` (it resolves to `renderToReadableStream`), and requires `"jsx": "react-jsx"` in `apps/api/tsconfig.json`. And the docs `/progress` islands: shadcn/ui (`recharts`, `radix-ui`, `class-variance-authority`, `clsx`, `tailwind-merge`) plus `d3-hierarchy` for the bubble packing, client-side in `apps/docs` only. Do not extend either exception to any other module.
 - Local GitHub auth falls back to `gh auth token`; scripts run fine outside Actions.
 
 ## Testing & QA

README.md

@@ -4,8 +4,8 @@
 
 <p align="center">
   <a href="https://x.com/basedprad"><img alt="follow" src="https://shieldcn.dev/x/follow/basedprad.svg" /></a>
-  <a href="https://lc.prad.nu"><img alt="badge" src="https://shieldcn.dev/badge/Read-Documentation.svg?logo=lu%3ABook" /></a>
-  <a href="https://lc.prad.nu/progress"><img alt="gate pass rate" src="https://srs-api.prdlk.workers.dev/badge/gate.svg" /></a>
+  <a href="https://leetcode.com/progress"><img alt="Custom badge" src="https://shieldcn.dev/badge/view-@prdlk.svg?logo=leetcode" /></a>
+  <a href="https://lc.prd.lk"><img alt="badge" src="https://shieldcn.dev/badge/Read-Documentation.svg?logo=lu%3ABook" /></a>
 </p>
 
 <p align="center">
@@ -337,4 +337,3 @@
     <tr><td align="center"><code>B</code></td><td align="center">252</td><td><a href="https://leetcode.com/problems/meeting-rooms/">Meeting Rooms I</a></td></tr>
   </tbody>
 </table>
-

apps/api/.dev.vars.example

@@ -1,3 +1,4 @@
 GH_PAT=github_pat_or_gho_token_with_issues_and_projects_rw
 WEBHOOK_SECRET=random_hex_matching_the_repo_webhook
 LINK_KEY=random_hex_signing_one_tap_links
+OPENROUTER_API_KEY=sk-or-v1_key_for_the_docs_assistant

apps/api/README.md

@@ -14,8 +14,12 @@ Live at `https://srs-api.prdlk.workers.dev`.
   labels, milestones. `catalog.ts` reconciles them into D1 nightly (and via
   `/admin/reconcile`); it recomputes from scratch, never invents rows, and
   never overwrites SRS-owned columns (`stage`, `next_review`).
-- **The repo owns the schedule** — `data/schedule.json`, human-edited,
-  bundled at deploy. Git history is its audit log.
+- **The repo owns the plan** — `data/schedule.json`, human-edited,
+  bundled at deploy. Git history is its audit log. Each date is a
+  `ScheduledDay`: `topics` (one or more topic issues), `problems` (a set day,
+  fixed numbers), `gate` (Saturday's blind set, verbatim), or `sweep` (redo
+  every miss, nothing new). Numbers a `gate` or `problems` entry names are
+  `RESERVED`: the drill and gate samplers never draw them.
 - The GitHub Project mirror writes `Target Date` and nothing else: it is
   best-effort, so failures log warnings and never block a D1 write, and topic
   rows are never written. SRS stage and first-attempt result stay in D1 only —
@@ -47,7 +51,10 @@ raw `Date` math.
 Blind drills draw only from topics **already learned**: scheduled in an
 earlier week (the current week's optional pool is reserved for Saturday's
 gate) and with at least one core problem on the ladder — a skipped learning
-day never feeds drills just because its calendar week lapsed.
+day never feeds drills just because its calendar week lapsed. A Saturday
+whose plan fixes the `gate` set uses that list as-is; every number must be a
+catalog row (a `set:optional` sub-issue of its topic), or the review issue is
+not created — a `/done` on an uncatalogued number could never be logged.
 
 ## Routes
 

apps/api/data/schedule.json

@@ -1,26 +1,28 @@
 {
-  "2026-08-17": 3,
-  "2026-08-18": 4,
-  "2026-08-24": 5,
-  "2026-08-25": 6,
-  "2026-08-26": 7,
-  "2026-08-27": 8,
-  "2026-08-28": 9,
-  "2026-08-31": 10,
-  "2026-09-01": 11,
-  "2026-09-02": 12,
-  "2026-09-03": 13,
-  "2026-09-04": 14,
-  "2026-09-07": 15,
-  "2026-09-08": 16,
-  "2026-09-09": 17,
-  "2026-09-10": 18,
-  "2026-09-11": 19,
-  "2026-09-14": 20,
-  "2026-09-15": 21,
-  "2026-09-16": 22,
-  "2026-09-17": 23,
-  "2026-09-18": 24,
-  "2026-09-21": 25,
-  "2026-09-22": 26
+  "2026-08-17": { "topics": [3] },
+  "2026-08-18": { "topics": [4] },
+  "2026-08-24": { "topics": [5] },
+  "2026-08-25": { "topics": [6] },
+  "2026-08-26": { "topics": [7] },
+  "2026-08-27": { "topics": [8] },
+  "2026-08-28": { "topics": [9] },
+  "2026-08-31": { "topics": [10] },
+  "2026-09-01": { "topics": [11] },
+  "2026-09-02": { "topics": [12] },
+  "2026-09-03": { "topics": [13] },
+  "2026-09-04": { "topics": [14] },
+  "2026-09-07": { "topics": [15] },
+  "2026-09-08": { "topics": [16] },
+  "2026-09-21": { "topics": [17, 18] },
+  "2026-09-22": { "topics": [19, 20] },
+  "2026-09-23": { "topics": [21] },
+  "2026-09-24": { "topics": [22] },
+  "2026-09-25": { "topics": [23] },
+  "2026-09-26": { "gate": [648, 1091, 802, 547, 90] },
+  "2026-09-28": { "topics": [24] },
+  "2026-09-29": { "topics": [25] },
+  "2026-09-30": { "topics": [26] },
+  "2026-10-01": { "problems": [399, 261, 909, 77, 52] },
+  "2026-10-02": { "sweep": true },
+  "2026-10-03": { "gate": [347, 1254, 1971, 131, 494, 986] }
 }

apps/api/src/ask.ts

@@ -0,0 +1,289 @@
+/**
+ * POST /ask — the docs assistant's backend.
+ *
+ * The docs are a static GitHub Pages site, and Blume's own assistant route is
+ * server-rendered (it reads the provider key per request), so the site points
+ * `ai.assistant.endpoint` here instead. This speaks the Blume island's wire
+ * contract (`blume/components/islands/hooks.ts`):
+ *
+ * - request: `{ messages: [{ role, content }], page: { path } }` as JSON,
+ *   `path` the base-stripped route the reader is on;
+ * - response: the answer as a plain UTF-8 text stream; any non-2xx shows the
+ *   island's error notice, and a 503 whose body starts "The assistant is not
+ *   configured" shows that body verbatim.
+ *
+ * Validation matches Blume's generated route: 1–40 user/assistant messages of
+ * string content, ≤ 24 000 chars serialized, a 64 KB body, and only role and
+ * content ever reach the model, so the endpoint cannot be repurposed as an
+ * open LLM proxy with a caller's own system prompt.
+ *
+ * Grounding reads what the site already publishes: `llms-full.txt`, every
+ * page's Markdown under `# Title` / `Source: <url>`. The page the reader is on
+ * goes in first, then the best keyword matches, within Blume's default budget
+ * (6 pages, 2 000 chars each, 10 000 total), under Blume's grounded system
+ * prompt — answer only from the excerpts, cite pages as `[Title](/route)`.
+ *
+ * The model call is OpenRouter's OpenAI-compatible chat endpoint over plain
+ * `fetch` (no SDK — see the repo's near-zero-dependency rule), streamed, with
+ * `reasoning.effort: "none"`, for the model the `ASK_MODEL` var names (a
+ * wrangler.jsonc change swaps it); its SSE deltas are re-emitted as bare text. The
+ * reader closing the panel aborts the request, which aborts the model call.
+ */
+
+const BODY_LIMIT = 64 * 1024;
+const MAX_MESSAGES = 40;
+const MAX_CHARS = 24_000;
+
+const MAX_RESULTS = 6;
+const EXCERPT_CHARS = 2000;
+const CONTEXT_BUDGET = 10_000;
+/** Lead-in kept before the matched region of a long page. */
+const EXCERPT_LEAD = 160;
+/** How long one isolate reuses the parsed corpus (the edge caches the fetch as long). */
+const CORPUS_TTL_MS = 5 * 60_000;
+
+const SYSTEM_PROMPT =
+  "You are a helpful documentation assistant for this project, a LeetCode interview-prep campaign: solved problems grouped by topic, with guides to the techniques behind them. Answer the user's question using ONLY the documentation excerpts below. Each excerpt is headed by its page as `## Page Title (/route)`. If the answer is not covered by the excerpts, say you don't know and suggest where in the docs to look — do not invent details. Always cite the pages you drew from, and write every citation as a Markdown link to that page using its route, e.g. [Page Title](/route).";
+
+/** Words that match everything and rank nothing. */
+const STOPWORDS = new Set(
+  "a an and are as at be but by can do does for from how i if in is it its me my of on or so that the this to was what when where which who why with you your".split(
+    " ",
+  ),
+);
+
+interface AskMessage {
+  role: "user" | "assistant";
+  content: string;
+}
+
+interface Section {
+  title: string;
+  route: string;
+  body: string;
+  /** Lower-cased title + body, searched per query term. */
+  text: string;
+  titleText: string;
+}
+
+// ── corpus ───────────────────────────────────────────────────────
+
+let corpus: { at: number; sections: Section[] } | undefined;
+
+/** `llms-full.txt` split into pages, cached per isolate for `CORPUS_TTL_MS`. */
+async function sections(docsUrl: string): Promise<Section[]> {
+  if (corpus && Date.now() - corpus.at < CORPUS_TTL_MS) return corpus.sections;
+  const res = await fetch(`${docsUrl}/llms-full.txt`, {
+    cf: { cacheTtl: CORPUS_TTL_MS / 1000, cacheEverything: true },
+  });
+  if (!res.ok) throw new Error(`GET llms-full.txt -> ${res.status}`);
+  const full = await res.text();
+  const heads = [...full.matchAll(/^# (.+)\nSource: (\S+)$/gm)];
+  const out = heads.map((head, i): Section => {
+    const start = head.index + head[0].length;
+    const end = heads[i + 1]?.index ?? full.length;
+    const body = full.slice(start, end).replace(/\n-{3,}\s*$/, "").trim();
+    const title = head[1]!.trim();
+    return {
+      title,
+      route: new URL(head[2]!).pathname.replace(/(.)\/+$/, "$1"),
+      body,
+      text: `${title}\n${body}`.toLowerCase(),
+      titleText: title.toLowerCase(),
+    };
+  });
+  corpus = { at: Date.now(), sections: out };
+  return out;
+}
+
+// ── retrieval ────────────────────────────────────────────────────
+
+function terms(text: string): string[] {
+  return [...new Set(text.toLowerCase().match(/[a-z0-9][a-z0-9+#-]*/g) ?? [])].filter(
+    (t) => !STOPWORDS.has(t) && (t.length > 1 || /\d/.test(t)),
+  );
+}
+
+function occurrences(haystack: string, needle: string): number {
+  let count = 0;
+  for (let at = haystack.indexOf(needle); at !== -1; at = haystack.indexOf(needle, at + needle.length)) count++;
+  return count;
+}
+
+/**
+ * The pages to inject, best first: term frequency damped by log and weighted
+ * by rarity across pages (idf), a title hit counting triple — so "217" or
+ * "sliding window" lands on the page named that rather than every page that
+ * mentions it in passing.
+ */
+function rank(all: Section[], query: string[]): Section[] {
+  const idf = new Map(
+    query.map((t) => [t, Math.log(1 + all.length / (1 + all.filter((s) => s.text.includes(t)).length))]),
+  );
+  return all
+    .map((section) => {
+      let score = 0;
+      for (const t of query) {
+        const tf = occurrences(section.text, t);
+        if (tf) score += idf.get(t)! * (Math.log(1 + tf) + (section.titleText.includes(t) ? 3 : 0));
+      }
+      return { section, score };
+    })
+    .filter((r) => r.score > 0)
+    .sort((a, b) => b.score - a.score)
+    .slice(0, MAX_RESULTS)
+    .map((r) => r.section);
+}
+
+/** A page whole when it fits, else `chars` from just before its first query hit. */
+function excerpt(section: Section, query: string[], chars: number): string {
+  if (section.body.length <= chars) return section.body;
+  const lower = section.body.toLowerCase();
+  const hits = query.map((t) => lower.indexOf(t)).filter((i) => i !== -1);
+  const start = hits.length ? Math.max(0, Math.min(...hits) - EXCERPT_LEAD) : 0;
+  return `${start > 0 ? "…" : ""}${section.body.slice(start, start + chars)}…`;
+}
+
+/** The system prompt: the current page, then the ranked pages, within the budget. */
+async function instructions(env: Env, messages: AskMessage[], path: string | undefined): Promise<string> {
+  const all = await sections(env.DOCS_URL);
+  // A follow-up ("and in Python?") leans on the question before it.
+  const asked = messages.filter((m) => m.role === "user").slice(-2).map((m) => m.content);
+  const query = terms(asked.join(" "));
+  const current = path ? all.find((s) => s.route === path) : undefined;
+  const picked = [...(current ? [current] : []), ...rank(all, query).filter((s) => s !== current)];
+  const parts: string[] = [];
+  let budget = CONTEXT_BUDGET;
+  for (const section of picked) {
+    if (budget < 200) break;
+    const text = excerpt(section, query, Math.min(EXCERPT_CHARS, budget));
+    parts.push(`## ${section.title} (${section.route})\n\n${text}`);
+    budget -= text.length;
+  }
+  return parts.length ? `${SYSTEM_PROMPT}\n\n# Documentation excerpts\n\n${parts.join("\n\n")}` : SYSTEM_PROMPT;
+}
+
+// ── request handling ─────────────────────────────────────────────
+
+/** The validated conversation, or a reason it was turned away. */
+function readMessages(body: unknown): AskMessage[] | undefined {
+  if (!body || typeof body !== "object" || !("messages" in body) || !Array.isArray(body.messages)) return;
+  const raw: unknown[] = body.messages;
+  if (raw.length === 0 || raw.length > MAX_MESSAGES || JSON.stringify(raw).length > MAX_CHARS) return;
+  const messages: AskMessage[] = [];
+  for (const m of raw) {
+    if (!m || typeof m !== "object" || !("role" in m) || !("content" in m)) return;
+    if ((m.role !== "user" && m.role !== "assistant") || typeof m.content !== "string") return;
+    messages.push({ role: m.role, content: m.content });
+  }
+  return messages;
+}
+
+function readPath(body: unknown): string | undefined {
+  if (!body || typeof body !== "object" || !("page" in body)) return;
+  const page = body.page;
+  if (!page || typeof page !== "object" || !("path" in page) || typeof page.path !== "string") return;
+  return page.path.replace(/(.)\/+$/, "$1");
+}
+
+/** OpenRouter's SSE (`data: {…choices[0].delta.content…}`) → the answer's bare text. */
+function textStream(sse: ReadableStream<Uint8Array>): ReadableStream<Uint8Array> {
+  const decoder = new TextDecoder();
+  const encoder = new TextEncoder();
+  let buffer = "";
+  return sse.pipeThrough(
+    new TransformStream<Uint8Array, Uint8Array>({
+      transform(chunk, controller) {
+        buffer += decoder.decode(chunk, { stream: true });
+        const lines = buffer.split("\n");
+        buffer = lines.pop() ?? "";
+        for (const line of lines) {
+          if (!line.startsWith("data: ")) continue; // `: OPENROUTER PROCESSING` keep-alives
+          const data = line.slice(6).trim();
+          if (data === "[DONE]") continue;
+          let event: unknown;
+          try {
+            event = JSON.parse(data);
+          } catch {
+            continue;
+          }
+          if (event && typeof event === "object" && "error" in event) {
+            // After the 200: the stream just ends, and the island shows its
+            // error notice for an empty answer.
+            console.error(`ask: provider error mid-stream: ${JSON.stringify(event.error)}`);
+            continue;
+          }
+          if (!event || typeof event !== "object" || !("choices" in event) || !Array.isArray(event.choices)) continue;
+          const choice: unknown = event.choices[0];
+          if (!choice || typeof choice !== "object" || !("delta" in choice)) continue;
+          const delta = choice.delta;
+          if (!delta || typeof delta !== "object" || !("content" in delta)) continue;
+          const content = delta.content;
+          if (typeof content === "string" && content) controller.enqueue(encoder.encode(content));
+        }
+      },
+    }),
+  );
+}
+
+export async function handleAsk(request: Request, env: Env): Promise<Response> {
+  // The docs serve from the custom domain and the Pages origin; reflect the
+  // requesting origin only when it is on the allowlist (as /api/stats does).
+  const allowed = env.DOCS_ORIGIN.split(",").map((o) => o.trim());
+  const origin = request.headers.get("origin");
+  const cors = {
+    "access-control-allow-origin": origin && allowed.includes(origin) ? origin : allowed[0]!,
+    "access-control-allow-methods": "POST",
+    "access-control-allow-headers": "content-type",
+    "access-control-max-age": "86400",
+    vary: "Origin",
+  };
+  const text = (body: string, status: number) =>
+    new Response(body, { status, headers: { ...cors, "content-type": "text/plain; charset=utf-8" } });
+
+  if (request.method === "OPTIONS") return new Response(null, { status: 204, headers: cors });
+  if (request.method !== "POST") return text("POST only.", 405);
+
+  const raw = await request.arrayBuffer();
+  if (raw.byteLength > BODY_LIMIT) return text("Request too large: the body must be at most 64 KB.", 413);
+  let body: unknown;
+  try {
+    body = JSON.parse(new TextDecoder().decode(raw));
+  } catch {
+    body = undefined;
+  }
+  const messages = readMessages(body);
+  if (!messages) return text("Invalid request: send 1-40 user/assistant messages with string content.", 400);
+  if (!env.OPENROUTER_API_KEY) return text("The assistant is not configured: set OPENROUTER_API_KEY.", 503);
+
+  let system: string;
+  try {
+    system = await instructions(env, messages, readPath(body));
+  } catch (err) {
+    // Ungrounded beats unanswered: the prompt still forbids inventing details.
+    console.warn(`ask: grounding unavailable: ${err}`);
+    system = SYSTEM_PROMPT;
+  }
+
+  const res = await fetch("https://openrouter.ai/api/v1/chat/completions", {
+    method: "POST",
+    headers: {
+      authorization: `Bearer ${env.OPENROUTER_API_KEY}`,
+      "content-type": "application/json",
+    },
+    body: JSON.stringify({
+      model: env.ASK_MODEL,
+      stream: true,
+      reasoning: { effort: "none" },
+      messages: [{ role: "system", content: system }, ...messages],
+    }),
+    signal: request.signal,
+  });
+  if (!res.ok || !res.body) {
+    console.error(`ask: POST /chat/completions -> ${res.status} ${await res.text().catch(() => "")}`);
+    return text("Failed to generate a response.", res.status === 429 ? 429 : 502);
+  }
+  return new Response(textStream(res.body), {
+    headers: { ...cors, "content-type": "text/plain; charset=utf-8", "cache-control": "no-store" },
+  });
+}

apps/api/src/catalog.ts

@@ -10,14 +10,11 @@
  * so relabelling a problem is enough to move it and titles stay readable.
  * The `problem` label is what marks a sub-issue as curriculum.
  */
-import { workingDay } from "./srs.ts";
+import { DIFFICULTIES, SETS, workingDay } from "./srs.ts";
 import type { GitHub } from "./github.ts";
 
 const TITLE_RE = /^LC (\d+) · (.+)$/;
 
-const DIFFICULTIES = ["easy", "medium", "hard"] as const;
-const SETS = ["core", "optional", "deferred"] as const;
-
 /** Deferred Hards enter the queue from this date, two per working day. */
 const DEFER_FROM = "2026-09-28";
 

apps/api/src/digest.ts

@@ -5,14 +5,16 @@
  * the HTML and the plain-text alternative from that single tree (React Email
  * `render`), so the two can never drift.
  *
- * Retrieval rules: review and drill rows carry number + difficulty only —
- * never the topic, never a solution link. `DigestRow` has no field for
- * either, so the rule holds by construction. The learning day's core list is
- * the only labeled section. At most REVIEW_CAP (3) reviews per day; drills
- * fill toward DAILY_CAP (6) only when the due queue is light. Overflow is
- * levelled, not stacked: sendDigest gives every review past the cap a
- * concrete future date, ≤ REVIEW_CAP per day, oldest first. Sunday is a
- * two-line rest note.
+ * Retrieval rules: review, drill and sweep rows carry number + difficulty
+ * only — never the topic, never a solution link. `DigestRow` has no field for
+ * either, so the rule holds by construction. The plan's own sections — a
+ * learning day's topics (core, then the optional "if time" list) and a set
+ * day's problems — are the only labeled, linked ones. At most REVIEW_CAP (3)
+ * reviews per day; drills fill toward DAILY_CAP (6) only when the due queue
+ * is light, and never on a sweep day, which assigns every open miss and
+ * nothing new. Overflow is levelled, not stacked: sendDigest gives every
+ * review past the cap a concrete future date, ≤ REVIEW_CAP per day, oldest
+ * first. Sunday is a two-line rest note.
  *
  * Idempotency: email_log keys sends by ET date — a same-day re-send is a
  * no-op unless forced; the body itself is deterministic (drill picks are
@@ -21,21 +23,25 @@
  */
 import {
   CAMPAIGN_DAYS,
+  MISS_WHERE,
   type ProblemRow,
+  RESERVED,
   REVIEW_CAP,
   SCHEDULE,
+  type ScheduledDay,
   addDays,
   campaignDay,
   campaignWeek,
   dueReviews,
   isoWeek,
   levelReviews,
+  lookupProblems,
   pickDrills,
   prettyDate,
   streak,
   weekdayOf,
 } from "./srs.ts";
-import { type DigestData, type DigestRow, renderDigest } from "./email.tsx";
+import { type DigestData, type DigestRow, type TopicRow, renderDigest } from "./email.tsx";
 import { signLink } from "./links.ts";
 
 /** Total daily ceiling: drills only fill what the whole due queue leaves. */
@@ -63,23 +69,49 @@ async function tapRow(env: Env, p: ProblemRow, date: string, staged: boolean): P
   };
 }
 
+/** A plan-named problem: linked to its issue, ticked once it has entered the ladder. */
+function topicRow(env: Env, p: ProblemRow): TopicRow {
+  return {
+    lc: p.lc_number,
+    difficulty: p.difficulty,
+    url: `https://github.com/${env.REPO}/issues/${p.issue}`,
+    solved: p.stage !== "new",
+  };
+}
+
+/** Problems whose most recent attempt failed — the miss log a sweep day works through. */
+async function openMisses(db: D1Database): Promise<ProblemRow[]> {
+  const { results } = await db
+    .prepare(
+      `SELECT p.* FROM problems p
+       JOIN attempts a ON a.lc_number = p.lc_number
+       WHERE ${MISS_WHERE}
+       ORDER BY a.date, p.lc_number`,
+    )
+    .all<ProblemRow>();
+  return results;
+}
+
 /** Everything the email needs, read straight out of D1 and the schedule. */
 export async function collectDigest(env: Env, date: string): Promise<DigestData> {
   const db = env.DB;
   const rest = weekdayOf(date) === 0;
+  const plan: ScheduledDay = rest ? {} : (SCHEDULE[date] ?? {});
 
   // Reviews surface at most REVIEW_CAP; drills fill toward DAILY_CAP only
   // when the WHOLE due queue is light — a heavy backlog must never trade
-  // review slots for brand-new drill problems.
+  // review slots for brand-new drill problems — and never on a sweep day.
   const due = rest ? [] : await dueReviews(db, date);
   const capped = due.slice(0, REVIEW_CAP);
-  const drills = rest ? [] : await pickDrills(db, date, DAILY_CAP - Math.min(due.length, DAILY_CAP));
+  const drills =
+    rest || plan.sweep ? [] : await pickDrills(db, date, DAILY_CAP - Math.min(due.length, DAILY_CAP));
 
   const data: DigestData = {
     day: prettyDate(date),
     progress: `Day ${campaignDay(date)} of ${CAMPAIGN_DAYS} · Week ${campaignWeek(date)}`,
     streak: await streak(db, date),
     rest,
+    topics: [],
     reviews: await Promise.all(capped.map((p) => tapRow(env, p, date, true))),
     carried: due.length - capped.length,
     drills: await Promise.all(drills.map((p) => tapRow(env, p, date, false))),
@@ -88,28 +120,42 @@ export async function collectDigest(env: Env, date: string): Promise<DigestData>
     progressUrl: `${env.DOCS_URL}/progress`,
   };
 
-  // New topic — the only section allowed to name problems and link them.
-  const topicIssue = rest ? undefined : SCHEDULE[date];
-  if (topicIssue !== undefined) {
+  // New topics — the plan's sections, the only ones allowed to name problems
+  // and link them. Core first; the optional set is "if time", minus anything
+  // the plan has reserved for a gate or a set day.
+  for (const topicIssue of plan.topics ?? []) {
     const topic = await db
       .prepare("SELECT name FROM topics WHERE issue = ?")
       .bind(topicIssue)
       .first<{ name: string }>();
-    const { results: core } = await db
+    const { results } = await db
       .prepare(
-        "SELECT * FROM problems WHERE topic_issue = ? AND set_label = 'core' ORDER BY lc_number",
+        "SELECT * FROM problems WHERE topic_issue = ? AND set_label IN ('core', 'optional') ORDER BY lc_number",
       )
       .bind(topicIssue)
       .all<ProblemRow>();
-    data.topic = {
+    data.topics.push({
       name: topic?.name ?? `#${topicIssue}`,
-      core: core.map((p) => ({
-        lc: p.lc_number,
-        difficulty: p.difficulty,
-        url: `https://github.com/${env.REPO}/issues/${p.issue}`,
-        solved: p.stage !== "new",
-      })),
-    };
+      core: results.filter((p) => p.set_label === "core").map((p) => topicRow(env, p)),
+      ifTime: results
+        .filter((p) => p.set_label === "optional" && !RESERVED.has(p.lc_number))
+        .map((p) => topicRow(env, p)),
+    });
+  }
+
+  // A set day assigns problems by number rather than by topic.
+  if (plan.problems) {
+    const { rows, missing } = await lookupProblems(db, plan.problems);
+    if (missing.length) console.warn(`digest ${date}: planned problems not in the catalog: ${missing.join(", ")}`);
+    data.assigned = rows.map((p) => topicRow(env, p));
+  }
+
+  // A sweep day works the miss log: every problem still standing on a
+  // failure, minus the ones today's review list already carries.
+  if (plan.sweep) {
+    const reviewed = new Set(capped.map((p) => p.lc_number));
+    const misses = (await openMisses(db)).filter((p) => !reviewed.has(p.lc_number));
+    data.sweep = await Promise.all(misses.map((p) => tapRow(env, p, date, true)));
   }
 
   // Saturday: the review issue already exists (created at midnight ET).

apps/api/src/email.tsx

@@ -83,7 +83,7 @@ export interface DigestRow {
   failUrl: string;
 }
 
-/** A learning-day core problem — the only rows allowed a link. */
+/** A plan-named problem — the only rows allowed a link. */
 export interface TopicRow {
   lc: number;
   difficulty: string;
@@ -91,6 +91,13 @@ export interface TopicRow {
   solved: boolean;
 }
 
+/** One learning-day topic: the core list, then the optional "if time" list. */
+export interface TopicSection {
+  name: string;
+  core: TopicRow[];
+  ifTime: TopicRow[];
+}
+
 export interface DigestData {
   /** "Tuesday, August 25" */
   day: string;
@@ -98,11 +105,16 @@ export interface DigestData {
   progress: string;
   streak: number;
   rest: boolean;
-  topic?: { name: string; core: TopicRow[] };
+  /** Topics taught today, in plan order — empty on every other day. */
+  topics: TopicSection[];
+  /** A set day's problems, assigned by number rather than by topic. */
+  assigned?: TopicRow[];
   reviews: DigestRow[];
   /** Reviews past the daily cap; levelled onto the coming days. */
   carried: number;
   drills: DigestRow[];
+  /** A sweep day's miss log: present (even empty) only on a sweep day. */
+  sweep?: DigestRow[];
   gate?: { week: number; url: string };
   yesterday: { total: number; failed: number[] };
   gateRate?: number;
@@ -278,10 +290,15 @@ function Block({
 // ── email ────────────────────────────────────────────────────────
 
 function DigestEmail({ data }: { data: DigestData }) {
-  const load = data.reviews.length + data.drills.length;
-  const preview = data.rest
-    ? "Rest day — nothing to do but rest."
-    : `${load} to work through today${data.topic ? `, starting with ${data.topic.name}` : ""}.`;
+  const load = data.reviews.length + data.drills.length + (data.sweep?.length ?? 0);
+  const lead = data.topics[0]
+    ? `, starting with ${data.topics[0].name}`
+    : data.assigned
+      ? ", starting with today's set"
+      : data.sweep
+        ? " — sweep day, nothing new"
+        : "";
+  const preview = data.rest ? "Rest day — nothing to do but rest." : `${load} to work through today${lead}.`;
 
   const passed = data.yesterday.total - data.yesterday.failed.length;
   const missed = data.yesterday.failed.map((lc) => `LC ${lc}`).join(", ");
@@ -310,15 +327,47 @@ function DigestEmail({ data }: { data: DigestData }) {
 
             {data.rest ? null : (
               <>
-                {data.topic ? (
-                  <Section style={{ marginTop: "28px" }}>
-                    <Text style={label}>Something new today</Text>
+                {data.topics.map((topic, i) => (
+                  <Section key={topic.name} style={{ marginTop: i === 0 ? "28px" : "20px" }}>
+                    {i === 0 ? (
+                      <Text style={label}>
+                        {data.topics.length === 1 ? "Something new today" : "Two new things today"}
+                      </Text>
+                    ) : null}
                     <Text style={{ color: INK, fontSize: "16px", fontWeight: 600, margin: "0 0 8px" }}>
-                      {data.topic.name}
+                      {topic.name}
                     </Text>
                     <Text style={hint}>Work through these from the top — a tick means it is already solved.</Text>
-                    <TopicTable rows={data.topic.core} />
+                    <TopicTable rows={topic.core} />
+                    {topic.ifTime.length > 0 ? (
+                      <>
+                        <Text style={{ ...hint, margin: "12px 0 8px" }}>
+                          If time — only once the core is done inside the clock.
+                        </Text>
+                        <TopicTable rows={topic.ifTime} />
+                      </>
+                    ) : null}
                   </Section>
+                ))}
+
+                {data.assigned ? (
+                  <Section style={{ marginTop: "28px" }}>
+                    <Text style={label}>Today's set</Text>
+                    <Text style={hint}>
+                      Picked by number, not by topic — all of them, in order, inside the clock.
+                    </Text>
+                    <TopicTable rows={data.assigned} />
+                  </Section>
+                ) : null}
+
+                {data.sweep ? (
+                  <Block
+                    title="Sweep — redo every red"
+                    note="Every problem still standing on a miss. Nothing new today; clear these first."
+                    rows={data.sweep}
+                    staged
+                    empty="The miss log is clear — nothing is standing on a fail."
+                  />
                 ) : null}
 
                 <Block
@@ -409,16 +458,27 @@ function plainDigest(data: DigestData): string {
           : ` · ${data.streak} day${data.streak === 1 ? "" : "s"} in a row, keep it going.`),
   ];
 
+  const linked = (p: TopicRow) =>
+    `  LC ${p.lc} — ${DIFFICULTY[p.difficulty]?.label ?? p.difficulty}${p.solved ? " (done)" : ""} — ${p.url}`;
+
   if (!data.rest) {
-    if (data.topic) {
+    for (const topic of data.topics) {
       out.push(
         "",
-        `SOMETHING NEW TODAY — ${data.topic.name}`,
+        `SOMETHING NEW TODAY — ${topic.name}`,
         "Work through these from the top; the ones marked done you have already solved.",
-        ...data.topic.core.map(
-          (p) =>
-            `  LC ${p.lc} — ${DIFFICULTY[p.difficulty]?.label ?? p.difficulty}${p.solved ? " (done)" : ""} — ${p.url}`,
-        ),
+        ...topic.core.map(linked),
+      );
+      if (topic.ifTime.length > 0) {
+        out.push("  If time — only once the core is done inside the clock:", ...topic.ifTime.map(linked));
+      }
+    }
+    if (data.assigned) {
+      out.push(
+        "",
+        "TODAY'S SET",
+        "Picked by number, not by topic — all of them, in order, inside the clock.",
+        ...data.assigned.map(linked),
       );
     }
 
@@ -436,6 +496,14 @@ function plainDigest(data: DigestData): string {
         "No cold starts today.",
       ],
     ];
+    if (data.sweep) {
+      lists.unshift([
+        "SWEEP — REDO EVERY RED",
+        "Every problem still standing on a miss. Nothing new today; clear these first.",
+        data.sweep,
+        "The miss log is clear — nothing is standing on a fail.",
+      ]);
+    }
     for (const [title, note, rows, empty] of lists) {
       out.push("", title);
       if (rows.length === 0) {

apps/api/src/gate.ts

@@ -2,21 +2,27 @@
  * Saturday review issue: created at midnight ET so the 8 AM digest can link
  * to it; scored when the issue closes (webhook).
  *
- * The gate half is a topic-blind quiz — one unsolved optional problem per
- * topic scheduled this week (which is why daily drills only draw from
- * earlier weeks). The recap half is generated data, deliberately NOT a task
- * list: the week's solved problems are already scheduled by the +3/+7 ladder,
- * and re-assigning them on Saturday would be massed practice.
+ * The gate half is a topic-blind quiz. When the plan fixes the set
+ * (`gate` in data/schedule.json) that list IS the gate, verbatim — every
+ * number must be a catalog problem, or the issue is not created, because a
+ * `/done` on an uncatalogued number can never be logged. Otherwise the set
+ * is sampled: one unsolved optional problem per topic scheduled this week
+ * (which is why daily drills only draw from earlier weeks), never one the
+ * plan has reserved. The recap half is generated data, deliberately NOT a
+ * task list: the week's solved problems are already scheduled by the +3/+7
+ * ladder, and re-assigning them on Saturday would be massed practice.
  *
  * Label is `review` (the retired Actions system owned `gate`). Creation is
- * idempotent by week; deferred Hards never appear.
+ * idempotent by week; deferred Hards never appear in a sampled set.
  */
 import {
   type ProblemRow,
+  RESERVED,
   type Result,
   SCHEDULE,
   campaignWeek,
   isoWeek,
+  lookupProblems,
   rng,
   sample,
   streak,
@@ -32,7 +38,7 @@ function capitalized(difficulty: string): string {
   return difficulty[0]!.toUpperCase() + difficulty.slice(1);
 }
 
-/** Unsolved problems of a topic in a set — never attempted, never drilled. */
+/** Unsolved problems of a topic in a set — never attempted, drilled, or reserved. */
 async function freshPool(db: D1Database, topic: number, set: string): Promise<ProblemRow[]> {
   const { results } = await db
     .prepare(
@@ -44,7 +50,7 @@ async function freshPool(db: D1Database, topic: number, set: string): Promise<Pr
     )
     .bind(topic, set)
     .all<ProblemRow>();
-  return results;
+  return results.filter((p) => !RESERVED.has(p.lc_number));
 }
 
 export interface CreateReport {
@@ -67,12 +73,24 @@ export async function createReviewIssue(env: Env, gh: GitHub, date: string): Pro
     return { created: false, issue: existing.issue, reason: `${title} exists (#${existing.issue})` };
   }
 
-  // Topics scheduled this week; review-only weeks (Sep 23 onward) sample
-  // across every topic that still has unsolved optional problems.
+  // The plan's fixed set wins; otherwise sample this week's topics, and in a
+  // week without topics, across every topic that still has an unsolved pool.
+  const picks: { p: ProblemRow; fallback: boolean }[] = [];
+  const planned = SCHEDULE[date]?.gate;
+  if (planned) {
+    const { rows, missing } = await lookupProblems(db, planned);
+    if (missing.length) {
+      return {
+        created: false,
+        reason: `planned gate names problems outside the catalog: LC ${missing.join(", LC ")}`,
+      };
+    }
+    picks.push(...rows.map((p) => ({ p, fallback: false })));
+  } else {
     let topics = Object.entries(SCHEDULE)
       .filter(([d]) => campaignWeek(d) === week)
       .sort(([a], [b]) => (a < b ? -1 : 1))
-    .map(([, t]) => t);
+      .flatMap(([, day]) => day.topics ?? []);
     if (topics.length === 0) {
       const { results } = await db
         .prepare(
@@ -89,7 +107,6 @@ export async function createReviewIssue(env: Env, gh: GitHub, date: string): Pro
     if (topics.length === 0) return { created: false, reason: "no topics with unsolved pools" };
 
     const random = rng(`gate-${iso}`);
-  const picks: { p: ProblemRow; fallback: boolean }[] = [];
     for (const topic of topics) {
       const optional = await freshPool(db, topic, "optional");
       if (optional.length > 0) {
@@ -101,6 +118,7 @@ export async function createReviewIssue(env: Env, gh: GitHub, date: string): Pro
       // Both pools exhausted: the topic is fully solved; nothing to quiz.
     }
     if (picks.length === 0) return { created: false, reason: `every pool for week ${week} is exhausted` };
+  }
 
   // Recap: everything attempted this week, plus streak — data, not tasks.
   const monday = weekMonday(date);
@@ -154,7 +172,7 @@ export async function createReviewIssue(env: Env, gh: GitHub, date: string): Pro
 
   const milestone = await db
     .prepare("SELECT milestone FROM topics WHERE issue = ? AND milestone IS NOT NULL")
-    .bind(topics[0])
+    .bind(picks[0]!.p.topic_issue)
     .first<{ milestone: number }>();
 
   const created = (await gh.rest(`/repos/${gh.repo}/issues`, {

apps/api/src/index.ts

@@ -9,6 +9,7 @@
  * Writes are owner-only (webhook author check, HMAC one-tap links, bearer
  * admin routes); everything else is read-only public.
  */
+import { handleAsk } from "./ask.ts";
 import { reconcileCatalog } from "./catalog.ts";
 import { gateBadge, heatmapChart, heatmapPng, ladderChart, progressChart } from "./charts.ts";
 import { sendDigest } from "./digest.ts";
@@ -322,6 +323,8 @@ export default {
       if (path.startsWith("/admin/") && request.method === "POST") {
         return await handleAdmin(request, env, path);
       }
+      // The docs assistant (the static Pages site's `ai.assistant.endpoint`).
+      if (path === "/ask") return await handleAsk(request, env);
 
       if (path === "/chart/progress.svg") {
         return new Response(await progressChart(env.DB), { headers: SVG_HEADERS });

apps/api/src/srs.test.ts

@@ -8,6 +8,8 @@ import { describe, expect, test } from "bun:test";
 
 import {
   INTERVAL,
+  RESERVED,
+  SCHEDULE,
   STAGES,
   WINDOWS,
   addDays,
@@ -19,6 +21,9 @@ import {
   isoWeek,
   rng,
   sample,
+  TEMPERATURES,
+  temperatureOf,
+  topicDate,
   weekdayOf,
   workingDay,
 } from "./srs.ts";
@@ -123,6 +128,38 @@ describe("the rest day", () => {
   });
 });
 
+describe("the plan", () => {
+  test("never books the rest day, and gates only on Saturday", () => {
+    for (const [date, day] of Object.entries(SCHEDULE)) {
+      expect(isRestDay(date)).toBe(false);
+      if (day.gate) expect(weekdayOf(date)).toBe(6);
+      if (day.topics) expect(weekdayOf(date)).toBeLessThan(6);
+    }
+  });
+
+  test("a topic is taught once; a doubled day answers for both", () => {
+    const seen = new Set<number>();
+    for (const day of Object.values(SCHEDULE)) {
+      for (const topic of day.topics ?? []) {
+        expect(seen.has(topic)).toBe(false);
+        seen.add(topic);
+      }
+    }
+    expect(topicDate(17)).toBe("2026-09-21");
+    expect(topicDate(18)).toBe("2026-09-21");
+    expect(topicDate(999)).toBeUndefined();
+  });
+
+  test("every gate and set problem is reserved from the samplers", () => {
+    for (const day of Object.values(SCHEDULE)) {
+      for (const lc of [...(day.gate ?? []), ...(day.problems ?? [])]) {
+        expect(RESERVED.has(lc)).toBe(true);
+      }
+    }
+    expect(RESERVED.size).toBeGreaterThan(0);
+  });
+});
+
 describe("the ladder", () => {
   test("two rungs, named after the windows", () => {
     expect(STAGES).toEqual(["new", "+3", "+7", "retired"]);
@@ -132,6 +169,31 @@ describe("the ladder", () => {
   });
 });
 
+describe("concept temperature", () => {
+  test("the bands are the ladder's own windows", () => {
+    // Boundaries are inclusive, and the bands tile the whole age axis with no
+    // gap: whatever the windows become, every age still lands in exactly one.
+    expect(TEMPERATURES).toEqual(["hot", "fresh", "fading", "cold"]);
+    expect(temperatureOf(0)).toBe("hot");
+    expect(temperatureOf(WINDOWS[0])).toBe("hot");
+    expect(temperatureOf(WINDOWS[0] + 1)).toBe("fresh");
+    expect(temperatureOf(WINDOWS[1])).toBe("fresh");
+    expect(temperatureOf(WINDOWS[1] + 1)).toBe("fading");
+    expect(temperatureOf(WINDOWS[1] * 2)).toBe("fading");
+    expect(temperatureOf(WINDOWS[1] * 2 + 1)).toBe("cold");
+  });
+
+  test("never attempted is cold, not unknown", () => {
+    expect(temperatureOf(null)).toBe("cold");
+  });
+
+  test("every age of the campaign has exactly one band", () => {
+    for (let age = 0; age <= CALENDAR.length; age++) {
+      expect(TEMPERATURES).toContain(temperatureOf(age));
+    }
+  });
+});
+
 describe("deterministic sampling", () => {
   test("same seed, same picks", () => {
     const pool = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

apps/api/src/srs.ts

@@ -1,6 +1,6 @@
 /**
- * SRS domain: ET dates, the work week, the interval ladder, deterministic
- * sampling, and the one write path for attempts.
+ * SRS domain: ET dates, the work week, the interval ladder, concept
+ * temperature, deterministic sampling, and the one write path for attempts.
  *
  * D1 is the single source of truth. The stage names the review a problem must
  * pass NEXT (`+3` = due 3 working days after the last clean solve). Passing
@@ -126,16 +126,50 @@ export function prettyDate(date: string): string {
 
 // ── the schedule (bundled; humans edit apps/api/data/schedule.json) ───
 
-export const SCHEDULE: Record<string, number> = scheduleJson;
+/**
+ * One calendar day of the plan. Most days teach topics (one, or two when the
+ * plan doubles up); the rest are named by what they assign instead: a fixed
+ * gate set for Saturday's review issue, a fixed problem set (a "B-set" day),
+ * or a sweep — redo every miss, nothing new. Absent dates are unplanned:
+ * the ladder still runs, the digest just has nothing new to say.
+ */
+export interface ScheduledDay {
+  /** Topic issues taught that day, in the order the digest presents them. */
+  topics?: number[];
+  /** Problems assigned by number instead of by topic. */
+  problems?: number[];
+  /** Saturday: the blind set, fixed by the plan rather than sampled. */
+  gate?: number[];
+  /** Miss-log sweep: every problem whose last attempt failed, and no new ones. */
+  sweep?: boolean;
+}
 
-/** Week in which a topic was (or will be) taught. */
-export function topicWeek(topic: number): number | undefined {
-  for (const [date, t] of Object.entries(SCHEDULE)) {
-    if (t === topic) return campaignWeek(date);
+export const SCHEDULE: Record<string, ScheduledDay> = scheduleJson;
+
+/** Date the schedule teaches a topic on, if it teaches it at all. */
+export function topicDate(topic: number): string | undefined {
+  for (const [date, day] of Object.entries(SCHEDULE)) {
+    if (day.topics?.includes(topic)) return date;
   }
   return undefined;
 }
 
+/** Week in which a topic was (or will be) taught. */
+export function topicWeek(topic: number): number | undefined {
+  const date = topicDate(topic);
+  return date === undefined ? undefined : campaignWeek(date);
+}
+
+/**
+ * Every problem the plan names outright — a gate's blind set or a set day's
+ * list. The plan owns these: the samplers (daily drills, a sampled gate)
+ * never draw them, so a gate problem stays unseen until its Saturday and a
+ * set day's problems wait for their day.
+ */
+export const RESERVED: ReadonlySet<number> = new Set(
+  Object.values(SCHEDULE).flatMap((day) => [...(day.gate ?? []), ...(day.problems ?? [])]),
+);
+
 // ── deterministic sampling ───────────────────────────────────────
 
 /** FNV-1a → mulberry32: seeded PRNG so re-runs pick identical problems. */
@@ -182,6 +216,45 @@ export const STAGES: Stage[] = ["new", "+3", "+7", "retired"];
 export type Result = "pass" | "fail";
 export type Kind = "first" | "review" | "drill" | "gate";
 
+/**
+ * Catalog vocabulary, carried by the `diff:*` / `set:*` issue labels and
+ * stored verbatim in `problems`. Listed low to high / most to least required,
+ * which is the order every chart, table and digest section prints them in.
+ */
+export const DIFFICULTIES = ["easy", "medium", "hard"] as const;
+export type Difficulty = (typeof DIFFICULTIES)[number];
+export const SETS = ["core", "optional", "deferred"] as const;
+export type SetLabel = (typeof SETS)[number];
+
+/**
+ * How warm a concept is: the age of a topic's most recent attempt, bucketed by
+ * the ladder's own windows so the two cannot drift. Touched inside the first
+ * window it is `hot`, inside the second `fresh`, inside one more full second
+ * window `fading`; older than that — or never attempted — it is `cold`.
+ *
+ * A read-side label only: nothing is scheduled off it. It answers the question
+ * the ladder cannot, because the ladder tracks problems and a topic can go
+ * quiet for a fortnight while not one of its problems comes due.
+ */
+export const TEMPERATURES = ["hot", "fresh", "fading", "cold"] as const;
+export type Temperature = (typeof TEMPERATURES)[number];
+
+/** Warmest band first, with the age it tolerates. Past the last one is cold. */
+const TEMPERATURE_MAX_AGE: [Temperature, number][] = [
+  ["hot", WINDOWS[0]],
+  ["fresh", WINDOWS[1]],
+  ["fading", WINDOWS[1] * 2],
+];
+
+/** Days since a topic's last attempt → its band; null (never) is cold. */
+export function temperatureOf(age: number | null): Temperature {
+  if (age === null) return "cold";
+  for (const [temperature, max] of TEMPERATURE_MAX_AGE) {
+    if (age <= max) return temperature;
+  }
+  return "cold";
+}
+
 export interface ProblemRow {
   lc_number: number;
   issue: number;
@@ -203,6 +276,31 @@ export async function getProblem(db: D1Database, lc: number): Promise<ProblemRow
   return db.prepare("SELECT * FROM problems WHERE lc_number = ?").bind(lc).first<ProblemRow>();
 }
 
+/**
+ * Catalog rows for a list of numbers the plan names, in the plan's order,
+ * plus the numbers the catalog does not know — a planned problem without an
+ * issue can never be logged, so callers decide whether that is fatal.
+ */
+export async function lookupProblems(
+  db: D1Database,
+  lcs: number[],
+): Promise<{ rows: ProblemRow[]; missing: number[] }> {
+  if (lcs.length === 0) return { rows: [], missing: [] };
+  const { results } = await db
+    .prepare(`SELECT * FROM problems WHERE lc_number IN (${lcs.map(() => "?").join(",")})`)
+    .bind(...lcs)
+    .all<ProblemRow>();
+  const byNumber = new Map(results.map((p) => [p.lc_number, p]));
+  const rows: ProblemRow[] = [];
+  const missing: number[] = [];
+  for (const lc of lcs) {
+    const row = byNumber.get(lc);
+    if (row) rows.push(row);
+    else missing.push(lc);
+  }
+  return { rows, missing };
+}
+
 /**
  * What "due" means, in one place: not retired, scheduled on/before ?1, and
  * past its deferral if it has one. Every caller that asks "what is open on
@@ -212,6 +310,15 @@ export async function getProblem(db: D1Database, lc: number): Promise<ProblemRow
 export const DUE_WHERE = `stage != 'retired' AND next_review IS NOT NULL AND next_review <= ?1
     AND (defer_until IS NULL OR defer_until <= ?1)`;
 
+/**
+ * What an open miss means, in one place: a problem `p` whose most recent
+ * attempt (highest id) failed and that has not retired. The sweep day works
+ * these and the stats' "attempting" count is how many there are, so the two
+ * cannot disagree. Expects `problems p` joined to `attempts a` on lc_number.
+ */
+export const MISS_WHERE = `a.id = (SELECT MAX(id) FROM attempts WHERE lc_number = p.lc_number)
+    AND a.result = 'fail' AND p.stage != 'retired'`;
+
 /** Reviews due on/before `date`, oldest first — the overflow carry order. */
 export async function dueReviews(db: D1Database, date: string): Promise<ProblemRow[]> {
   const { results } = await db
@@ -313,8 +420,9 @@ export async function levelReviews(db: D1Database, date: string): Promise<number
  * scheduled in an earlier week (the current week's optional pool is reserved
  * for Saturday's gate) AND showing learning evidence: at least one of the
  * topic's core problems has entered the ladder. A skipped learning day never
- * feeds drills just because its calendar week lapsed. Never repeated,
- * seeded by date. Boosted topics contribute up to 2 extra.
+ * feeds drills just because its calendar week lapsed. Problems the plan names
+ * outright (RESERVED) are never drawn. Never repeated, seeded by date.
+ * Boosted topics contribute up to 2 extra.
  */
 export async function pickDrills(
   db: D1Database,
@@ -337,6 +445,7 @@ export async function pickDrills(
     )
     .all<ProblemRow & { boost: number }>();
   const pool = results.filter((p) => {
+    if (RESERVED.has(p.lc_number)) return false;
     const w = topicWeek(p.topic_issue);
     return w !== undefined && w < week;
   });

apps/api/src/stats.ts

@@ -1,19 +1,34 @@
 /**
- * GET /api/stats — the one JSON document behind the docs progress page.
- * Read-only aggregation over D1; shape is the page's contract, change both
- * together. A problem counts as "done" once it entered the ladder
- * (stage != 'new').
+ * GET /api/stats — the one JSON document behind the docs progress page and the
+ * `bun run stats` terminal dashboard. Read-only aggregation over D1; the shape
+ * is both readers' contract, so change all three together. A problem counts as
+ * "done" once it entered the ladder (stage != 'new').
+ *
+ * The temperature block is the one figure here that is not a count of rows:
+ * srs.ts turns a topic's days-since-last-attempt into a band, so "which
+ * concepts have gone cold" has exactly one definition and the dashboard is
+ * free to colour it however it likes.
+ *
+ * `recent`, `attempting` and `year` feed the docs page's LeetCode-style cards
+ * (recently solved, the solved ring, the heatmap and the submissions chart).
+ * They are additive: the terminal dashboard ignores them.
  */
 import {
   CAMPAIGN_DAYS,
   CAMPAIGN_START,
+  DIFFICULTIES,
   DUE_WHERE,
+  MISS_WHERE,
   addDays,
   campaignDay,
   campaignWeek,
+  daysBetween,
   isoWeek,
   STAGES,
   streak,
+  temperatureOf,
+  topicDate,
+  type Temperature,
 } from "./srs.ts";
 
 const PHASE_NAMES: Record<number, string> = {
@@ -24,6 +39,97 @@ const PHASE_NAMES: Record<number, string> = {
   5: "V — Decision Space",
 };
 
+/** One concept: catalog coverage plus how long since it was last exercised. */
+interface TopicStat {
+  issue: number;
+  name: string;
+  milestone: number | null;
+  /** Campaign week the schedule teaches it in; null when unscheduled. */
+  week: number | null;
+  /** False while the schedule has not reached it — temperature is moot. */
+  taught: boolean;
+  total: number;
+  done: number;
+  retired: number;
+  due: number;
+  /** ET date of the most recent attempt on any of its problems. */
+  last: string | null;
+  /** Days since `last`; null when never attempted. */
+  age: number | null;
+  temperature: Temperature;
+}
+
+/** Days in `year`: the 365 ending today, which always covers the current calendar year to date. */
+const YEAR_DAYS = 365;
+
+/** How many problems `recent` lists. */
+const RECENT_LIMIT = 10;
+
+async function buildTopics(db: D1Database, today: string): Promise<TopicStat[]> {
+  // Three shapes, three statements: batch() carries one row type, and casting
+  // its results apart would cost more than the round trips it saves.
+  const { results: coverage } = await db
+    .prepare(
+      `SELECT t.issue AS issue, t.name AS name, t.milestone AS milestone,
+              COUNT(p.lc_number) AS total,
+              SUM(CASE WHEN p.stage != 'new' THEN 1 ELSE 0 END) AS done,
+              SUM(CASE WHEN p.stage = 'retired' THEN 1 ELSE 0 END) AS retired
+       FROM topics t LEFT JOIN problems p ON p.topic_issue = t.issue
+       GROUP BY t.issue
+       ORDER BY t.issue`,
+    )
+    .all<{
+      issue: number;
+      name: string;
+      milestone: number | null;
+      total: number;
+      done: number | null;
+      retired: number | null;
+    }>();
+
+  const { results: activity } = await db
+    .prepare(
+      `SELECT p.topic_issue AS issue, MAX(a.date) AS last
+       FROM attempts a JOIN problems p ON p.lc_number = a.lc_number
+       GROUP BY p.topic_issue`,
+    )
+    .all<{ issue: number; last: string | null }>();
+  const lastByTopic = new Map<number, string>();
+  for (const row of activity) {
+    if (row.last) lastByTopic.set(row.issue, row.last);
+  }
+
+  const { results: dueRows } = await db
+    .prepare(
+      `SELECT topic_issue AS issue, COUNT(*) AS n
+       FROM problems WHERE ${DUE_WHERE} GROUP BY topic_issue`,
+    )
+    .bind(today)
+    .all<{ issue: number; n: number }>();
+  const dueByTopic = new Map<number, number>();
+  for (const row of dueRows) dueByTopic.set(row.issue, row.n);
+
+  return coverage.map((row) => {
+    const taughtOn = topicDate(row.issue);
+    const last = lastByTopic.get(row.issue) ?? null;
+    const age = last === null ? null : daysBetween(last, today);
+    return {
+      issue: row.issue,
+      name: row.name,
+      milestone: row.milestone,
+      week: taughtOn === undefined ? null : campaignWeek(taughtOn),
+      taught: taughtOn !== undefined && taughtOn <= today,
+      total: row.total,
+      done: row.done ?? 0,
+      retired: row.retired ?? 0,
+      due: dueByTopic.get(row.issue) ?? 0,
+      last,
+      age,
+      temperature: temperatureOf(age),
+    };
+  });
+}
+
 export async function buildStats(db: D1Database, today: string): Promise<object> {
   const { results: phaseRows } = await db
     .prepare(
@@ -65,6 +171,21 @@ export async function buildStats(db: D1Database, today: string): Promise<object>
   const ladder: Record<string, number> = Object.fromEntries(STAGES.map((s) => [s, 0]));
   for (const row of ladderRows) ladder[row.stage] = row.n;
 
+  // Same shape as `ladder`: every band present, zeros included, in DIFFICULTIES
+  // order so a reader can index it without sorting.
+  const { results: diffRows } = await db
+    .prepare(
+      `SELECT difficulty,
+              COUNT(*) AS total,
+              SUM(CASE WHEN stage != 'new' THEN 1 ELSE 0 END) AS done
+       FROM problems GROUP BY difficulty`,
+    )
+    .all<{ difficulty: string; total: number; done: number }>();
+  const difficulty = DIFFICULTIES.map((name) => {
+    const row = diffRows.find((r) => r.difficulty === name);
+    return { difficulty: name, total: row?.total ?? 0, done: row?.done ?? 0 };
+  });
+
   // gates rows are keyed by ISO week (that's the digest/gate contract), but
   // the page speaks campaign weeks. The campaign never crosses a year
   // boundary, so a plain offset converts safely.
@@ -74,29 +195,108 @@ export async function buildStats(db: D1Database, today: string): Promise<object>
     .all<{ week: number; issue: number | null; pass_rate: number | null; closed_on: string | null }>();
   const gates = gateRows.map((g) => ({ ...g, week: g.week - isoWeekOffset }));
 
-  // Review-queue depth for the next 14 days: everything due by that day.
-  const queue: { date: string; due: number }[] = [];
-  for (let i = 0; i < 14; i++) {
-    const date = addDays(today, i);
-    const row = await db
-      .prepare(`SELECT COUNT(*) AS n FROM problems WHERE ${DUE_WHERE}`)
-      .bind(date)
-      .first<{ n: number }>();
-    queue.push({ date, due: row?.n ?? 0 });
-  }
+  // Review-queue depth for the next 14 days: everything due by that day. One
+  // statement per day, but DUE_WHERE stays the only definition of "due" — the
+  // batch is a single round trip, not fourteen.
+  const dates = Array.from({ length: 14 }, (_, i) => addDays(today, i));
+  const queueRows = await db.batch<{ n: number }>(
+    dates.map((date) =>
+      db.prepare(`SELECT COUNT(*) AS n FROM problems WHERE ${DUE_WHERE}`).bind(date),
+    ),
+  );
+  const queue = dates.map((date, i) => ({ date, due: queueRows[i]?.results[0]?.n ?? 0 }));
 
-  const recent: { date: string; attempts: number; passes: number }[] = [];
-  for (let i = 6; i >= 0; i--) {
-    const date = addDays(today, -i);
-    const row = await db
+  // Attempts per campaign day, every day present. This is the README heatmap's
+  // data model — the terminal dashboard lays it out by campaign week and reads
+  // its tail for "last 14 days" rather than asking a second question.
+  const end = addDays(CAMPAIGN_START, CAMPAIGN_DAYS - 1);
+  const { results: heatRows } = await db
     .prepare(
-        `SELECT COUNT(*) AS attempts,
+      `SELECT date,
+              COUNT(*) AS attempts,
               SUM(CASE WHEN result = 'pass' THEN 1 ELSE 0 END) AS passes
-         FROM attempts WHERE date = ?`,
+       FROM attempts WHERE date BETWEEN ?1 AND ?2 GROUP BY date`,
     )
-      .bind(date)
-      .first<{ attempts: number; passes: number | null }>();
-    recent.push({ date, attempts: row?.attempts ?? 0, passes: row?.passes ?? 0 });
+    .bind(CAMPAIGN_START, end)
+    .all<{ date: string; attempts: number; passes: number | null }>();
+  const byDate = new Map(heatRows.map((r) => [r.date, r]));
+  const heat = Array.from({ length: CAMPAIGN_DAYS }, (_, i) => {
+    const date = addDays(CAMPAIGN_START, i);
+    const row = byDate.get(date);
+    return { date, attempts: row?.attempts ?? 0, passes: row?.passes ?? 0 };
+  });
+
+  // The ten problems most recently solved, dated by each one's FIRST passing
+  // attempt — when it was completed, not when it was last re-solved (LeetCode's
+  // "Recent AC"). Same-day ties fall back to log order.
+  const { results: recentRows } = await db
+    .prepare(
+      `SELECT p.lc_number AS lc, p.title AS title, p.difficulty AS difficulty,
+              MIN(a.date) AS date, MIN(a.id) AS seq
+       FROM attempts a JOIN problems p ON p.lc_number = a.lc_number
+       WHERE a.result = 'pass'
+       GROUP BY p.lc_number
+       ORDER BY date DESC, seq DESC
+       LIMIT ?1`,
+    )
+    .bind(RECENT_LIMIT)
+    .all<{ lc: number; title: string; difficulty: string; date: string; seq: number }>();
+  const recent = recentRows.map(({ lc, title, difficulty, date }) => ({ lc, title, difficulty, date }));
+
+  // Problems still standing on a failure — the sweep day's miss log, counted.
+  const missRow = await db
+    .prepare(
+      `SELECT COUNT(*) AS n FROM problems p
+       JOIN attempts a ON a.lc_number = p.lc_number
+       WHERE ${MISS_WHERE}`,
+    )
+    .first<{ n: number }>();
+
+  // The past year, one entry per day (zeros included), split by difficulty two
+  // ways: every logged attempt, and every first solve — the same first-pass
+  // date `recent` uses. `heat` stays campaign-scoped (the terminal dashboard
+  // lays it out by campaign week); this is the calendar-scoped view the docs
+  // heatmap and submissions chart window and bucket for themselves.
+  const yearStart = addDays(today, -(YEAR_DAYS - 1));
+  const { results: attemptRows } = await db
+    .prepare(
+      `SELECT a.date AS date, p.difficulty AS difficulty,
+              COUNT(*) AS n,
+              SUM(CASE WHEN a.result = 'pass' THEN 1 ELSE 0 END) AS passes
+       FROM attempts a JOIN problems p ON p.lc_number = a.lc_number
+       WHERE a.date BETWEEN ?1 AND ?2
+       GROUP BY a.date, p.difficulty`,
+    )
+    .bind(yearStart, today)
+    .all<{ date: string; difficulty: string; n: number; passes: number | null }>();
+  const { results: solvedRows } = await db
+    .prepare(
+      `SELECT date, difficulty, COUNT(*) AS n
+       FROM (SELECT MIN(a.date) AS date, p.difficulty AS difficulty
+             FROM attempts a JOIN problems p ON p.lc_number = a.lc_number
+             WHERE a.result = 'pass'
+             GROUP BY p.lc_number)
+       WHERE date BETWEEN ?1 AND ?2
+       GROUP BY date, difficulty`,
+    )
+    .bind(yearStart, today)
+    .all<{ date: string; difficulty: string; n: number }>();
+  const year = Array.from({ length: YEAR_DAYS }, (_, i) => ({
+    date: addDays(yearStart, i),
+    passes: 0,
+    attempts: Object.fromEntries(DIFFICULTIES.map((d) => [d, 0])),
+    solved: Object.fromEntries(DIFFICULTIES.map((d) => [d, 0])),
+  }));
+  const yearIndex = new Map(year.map((d, i) => [d.date, i]));
+  for (const row of attemptRows) {
+    const day = year[yearIndex.get(row.date) ?? -1];
+    if (!day || !(row.difficulty in day.attempts)) continue;
+    day.attempts[row.difficulty] = row.n;
+    day.passes += row.passes ?? 0;
+  }
+  for (const row of solvedRows) {
+    const day = year[yearIndex.get(row.date) ?? -1];
+    if (day && row.difficulty in day.solved) day.solved[row.difficulty] = row.n;
   }
 
   return {
@@ -104,9 +304,14 @@ export async function buildStats(db: D1Database, today: string): Promise<object>
     campaign: { day: campaignDay(today), week: campaignWeek(today), start: CAMPAIGN_START, days: CAMPAIGN_DAYS },
     phases: [...phases.values()],
     ladder,
+    difficulty,
+    attempting: missRow?.n ?? 0,
+    topics: await buildTopics(db, today),
     gates,
     streak: await streak(db, today),
     queue,
+    heat,
     recent,
+    year,
   };
 }

apps/api/wrangler.jsonc

@@ -32,10 +32,15 @@
     "REPO": "prdlk/leetcode",
     "FROM_EMAIL": "srs@prdlk.com",
     "TO_EMAIL": "prnk28@gmail.com",
-    "DOCS_URL": "https://prdlk.github.io/leetcode",
-    "DOCS_ORIGIN": "https://prdlk.github.io,https://lc.prad.nu",
-    "PUBLIC_URL": "https://srs-api.prdlk.workers.dev"
+    "DOCS_URL": "https://lc.prd.lk",
+    "DOCS_ORIGIN": "https://lc.prd.lk,https://prdlk.github.io",
+    "PUBLIC_URL": "https://srs-api.prdlk.workers.dev",
+    // The docs assistant's OpenRouter model (POST /ask). `:free` variants share
+    // an upstream pool and answer 429 when it is saturated.
+    "ASK_MODEL": "qwen/qwen3.8-27b:free"
   }
 
   // Secrets (wrangler secret put): GH_PAT, WEBHOOK_SECRET, LINK_KEY.
+  // OPENROUTER_API_KEY (the docs assistant, POST /ask) is the repo's Actions
+  // secret of that name, put by deploy.yml before every deploy.
 }

apps/cli/api.ts

@@ -0,0 +1,87 @@
+/**
+ * The SRS Worker, from the CLI side: one base URL and one read-side payload.
+ *
+ * `SRS_API` points a script at a `wrangler dev` instance instead of production
+ * — the same switch close-solved.ts uses for its `/admin/solved` push, which is
+ * why the default lives here rather than in either script.
+ *
+ * The payload is narrowed with a guard rather than cast: D1 is the only source
+ * of SRS truth, so if the Worker answers something else the caller must say so
+ * out loud, not render half a dashboard off undefined fields.
+ */
+import { STAGES, TEMPERATURES, type Stage, type Temperature } from "../api/src/srs.ts";
+
+export const SRS_API = process.env.SRS_API ?? "https://srs-api.prdlk.workers.dev";
+
+// The rungs and the bands come straight from the Worker's domain module — the
+// same import work.ts makes for WINDOWS — so a change to either vocabulary
+// reaches this dashboard without a second list to remember.
+export { STAGES, TEMPERATURES, type Stage, type Temperature };
+
+export interface Phase {
+  milestone: number;
+  name: string;
+  core_done: number;
+  core_total: number;
+  optional_done: number;
+  optional_total: number;
+  deferred_done: number;
+  deferred_total: number;
+}
+
+export interface Topic {
+  issue: number;
+  name: string;
+  milestone: number | null;
+  week: number | null;
+  taught: boolean;
+  total: number;
+  done: number;
+  retired: number;
+  due: number;
+  last: string | null;
+  age: number | null;
+  temperature: Temperature;
+}
+
+export interface Stats {
+  generated: string;
+  campaign: { day: number; week: number; start: string; days: number };
+  phases: Phase[];
+  ladder: Record<Stage, number>;
+  difficulty: { difficulty: string; total: number; done: number }[];
+  topics: Topic[];
+  /** week is the 1-based campaign week — the Worker converts from ISO. */
+  gates: { week: number; issue: number | null; pass_rate: number | null; closed_on: string | null }[];
+  streak: number;
+  queue: { date: string; due: number }[];
+  /** Every campaign day, zeros and future days included. */
+  heat: { date: string; attempts: number; passes: number }[];
+}
+
+function isStats(value: unknown): value is Stats {
+  if (typeof value !== "object" || value === null) return false;
+  const v = value as Record<string, unknown>;
+  return (
+    typeof v.campaign === "object" &&
+    v.campaign !== null &&
+    typeof v.ladder === "object" &&
+    v.ladder !== null &&
+    typeof v.streak === "number" &&
+    Array.isArray(v.phases) &&
+    Array.isArray(v.difficulty) &&
+    Array.isArray(v.topics) &&
+    Array.isArray(v.gates) &&
+    Array.isArray(v.queue) &&
+    Array.isArray(v.heat)
+  );
+}
+
+/** GET /api/stats. Throws with the reason; there is no local substitute. */
+export async function fetchStats(signal?: AbortSignal): Promise<Stats> {
+  const res = await fetch(`${SRS_API}/api/stats`, { signal });
+  if (!res.ok) throw new Error(`GET /api/stats -> ${res.status} ${await res.text()}`);
+  const body: unknown = await res.json();
+  if (!isStats(body)) throw new Error("GET /api/stats -> unrecognised payload shape");
+  return body;
+}

apps/cli/close-solved.ts

@@ -21,6 +21,7 @@
  */
 import { join } from "node:path";
 
+import { SRS_API } from "./api.ts";
 import { github } from "./github.ts";
 import { markdownTable, printTable, writeStepSummary } from "./report.ts";
 import { isImplemented } from "./source.ts";
@@ -162,7 +163,8 @@ for (const num of [...work.keys()].sort((a, b) => a - b)) {
 // rung named, so the whole implemented set can go over on every push (a total
 // recompute that backfills whatever earlier runs missed) and re-runs write
 // nothing.
-const SRS_API = process.env.SRS_API ?? "https://srs-api.prdlk.workers.dev";
+// SRS_API (apps/cli/api.ts) is the switch that points this at a wrangler dev
+// instance instead of production.
 const solved = [...work.entries()]
   .flatMap(([lc, entry]) => [...entry.solved].sort().map((bucket) => ({ lc, bucket })))
   .sort((a, b) => a.lc - b.lc || a.bucket - b.bucket);

apps/cli/close-topics.ts

@@ -7,6 +7,7 @@
  * `set:optional` and `set:deferred` are extra credit. A topic is finished when
  * every one of its core sub-issues is closed; optional/deferred state is
  * ignored, matching the day rule in each topic body ("Core problems first").
+ * The rule lives in topics.ts, shared with release-topics.ts.
  *
  * Like close-solved.ts this reconciles state instead of reacting to an event
  * payload: re-runs are no-ops, backfilling needs no special casing, and only
@@ -19,6 +20,7 @@
  */
 import { github } from "./github.ts";
 import { markdownTable, printTable, writeStepSummary } from "./report.ts";
+import { coreSet, readProblems } from "./topics.ts";
 
 const DRY =
   process.argv.includes("--dry-run") ||
@@ -53,52 +55,13 @@ for await (const raw of gh.list(`/repos/${gh.repo}/issues?labels=topic&state=ope
 }
 topics.sort((a, b) => a.number - b.number);
 
-// ── core sub-issue state per topic ───────────────────────────────
-
-interface Core {
-  /** Core sub-issues, closed and open alike, lowest number first. */
-  all: number[];
-  /** The core sub-issues still open — non-empty means the topic stays open. */
-  pending: number[];
-}
-
-/**
- * Read a topic's core sub-issue state. The sub_issues payload carries the full
- * issue objects (state + labels), so no per-problem follow-up request is needed.
- */
-async function readCore(topic: number): Promise<Core> {
-  const all: number[] = [];
-  const pending: number[] = [];
-  for await (const raw of gh.list(`/repos/${gh.repo}/issues/${topic}/sub_issues`)) {
-    if (!raw || typeof raw !== "object") continue;
-    if (!("number" in raw) || typeof raw.number !== "number") continue;
-    if (!("state" in raw) || typeof raw.state !== "string") continue;
-    if (!("labels" in raw) || !Array.isArray(raw.labels)) continue;
-
-    const core = raw.labels.some(
-      (label) =>
-        label &&
-        typeof label === "object" &&
-        "name" in label &&
-        label.name === "set:core",
-    );
-    if (!core) continue;
-
-    all.push(raw.number);
-    if (raw.state === "open") pending.push(raw.number);
-  }
-  all.sort((a, b) => a - b);
-  pending.sort((a, b) => a - b);
-  return { all, pending };
-}
-
 // ── reconcile ────────────────────────────────────────────────────
 
 const report: string[][] = [];
 let closed = 0;
 
 for (const topic of topics) {
-  const core = await readCore(topic.number);
+  const core = coreSet(await readProblems(gh, topic.number));
   const progress = `${core.all.length - core.pending.length}/${core.all.length}`;
 
   // A topic with no core sub-issues has nothing to complete: never close it,

apps/cli/package.json

@@ -4,15 +4,18 @@
   "type": "module",
   "scripts": {
     "pick": "bun ./pick.ts",
+    "stats": "bun ./stats.ts",
     "test": "bun ./test.ts",
     "submit": "bun ./submit.ts",
     "sync": "bun ./sync.ts",
+    "videos": "bun ./videos.ts",
     "close-solved": "bun ./close-solved.ts",
-    "close-topics": "bun ./close-topics.ts"
+    "close-topics": "bun ./close-topics.ts",
+    "release-topics": "bun ./release-topics.ts"
   },
   "devDependencies": {
     "@clack/prompts": "^1.7.0",
-    "@night-slayer18/leetcode-cli": "^3.5.0",
+    "@night-slayer18/leetcode-cli": "^3.5.2",
     "@types/bun": "^1.3.14"
   }
 }

apps/cli/release-topics.ts

@@ -0,0 +1,340 @@
+#!/usr/bin/env bun
+/**
+ * Publish one GitHub release per finished topic, versioned by timever
+ * (`YYYYMMDD.HHMMSS.NNNNNNNNN`, UTC — https://gist.github.com/twolfson/de1b004dd22536b8e668).
+ *
+ * "Finished" is topics.ts's rule — every core sub-issue closed — the same one
+ * close-topics.ts closes the topic issue on, and the version is the instant
+ * the LAST core problem closed. Keying off the sub-issues rather than the
+ * topic issue lets this run as the tail of Close Solved: the push that closes
+ * a topic's final core problem releases it in the same run, without waiting
+ * for close-topics to chain after it. The topic issue itself closes seconds
+ * later, on the same day.
+ *
+ * Each release is a changelog snapshot at that instant: the topic's problem
+ * sub-issues grouped as closed on the finish day (ET), closed earlier, and
+ * open at release, each with its set, difficulty, and the solution files as
+ * they stood in the tagged commit — the last main commit before the finish.
+ *
+ * The tag is annotated and backdated (tagger date = finish), so
+ * `git tag --sort=taggerdate` reads as the campaign's history even for tags
+ * minted by a backfill. The release's own published date cannot be backdated
+ * (the API has no field for it), so the docs changelog dates each entry from
+ * this timever tag instead (`releasesDatedByTag` in apps/docs/blume.config.ts)
+ * — the tag format is that contract.
+ *
+ * Reconciles instead of reacting: every finished topic without a release gets
+ * one, so a first run backfills the whole campaign; an existing release keeps
+ * its tag and commit and only has its body rewritten when render() would say
+ * something else. Re-runs with nothing new are no-ops.
+ * A release is found by the marker comment in its body, never by tag name, so
+ * reopening and re-closing a core problem can never mint a second release.
+ * A tag that exists without its release (a run that died between the two) is
+ * reused, not re-created.
+ *
+ *   bun apps/cli/release-topics.ts            # tag, push, release, fix bodies
+ *   bun apps/cli/release-topics.ts --dry-run  # print the would-be releases
+ *
+ * Auth: GH_TOKEN / GITHUB_TOKEN, else `gh auth token` (needs contents: write).
+ * Git:  a clone with full history, an `origin` it may push tags to, and a
+ *       committer identity (the tagger).
+ */
+import { etDate } from "../api/src/srs.ts";
+import { github } from "./github.ts";
+import { markdownTable, printTable, writeStepSummary } from "./report.ts";
+import { coreSet, labelValue, readProblems, type Problem } from "./topics.ts";
+import { ROOT, parseWorkPath } from "./work.ts";
+
+const DRY =
+  process.argv.includes("--dry-run") ||
+  process.env.DRY_RUN === "1" ||
+  process.env.DRY_RUN === "true";
+
+/** The docs site (apps/docs/blume.config.ts `deployment.site`); sync publishes `/<num>` short links. */
+const DOCS_SITE = "https://lc.prd.lk";
+const TIMEVER = "https://gist.github.com/twolfson/de1b004dd22536b8e668";
+
+const gh = await github();
+
+function git(...args: string[]): string {
+  const run = Bun.spawnSync(["git", ...args], { cwd: ROOT });
+  if (run.exitCode !== 0) throw new Error(`git ${args.join(" ")}: ${run.stderr.toString().trim()}`);
+  return run.stdout.toString().trim();
+}
+
+// ── topics ───────────────────────────────────────────────────────
+
+interface Topic {
+  number: number;
+  title: string;
+  milestone: string | null;
+  body: string;
+}
+
+/** Narrow one /issues element; the `topic` label filter cannot exclude PRs. */
+function readTopic(value: unknown): Topic | undefined {
+  if (!value || typeof value !== "object") return;
+  if ("pull_request" in value) return;
+  if (!("number" in value) || typeof value.number !== "number") return;
+  if (!("title" in value) || typeof value.title !== "string") return;
+  const milestone =
+    "milestone" in value &&
+    value.milestone &&
+    typeof value.milestone === "object" &&
+    "title" in value.milestone &&
+    typeof value.milestone.title === "string"
+      ? value.milestone.title
+      : null;
+  const body = "body" in value && typeof value.body === "string" ? value.body : "";
+  return { number: value.number, title: value.title, milestone, body };
+}
+
+interface Finished {
+  topic: Topic;
+  problems: Problem[];
+  core: number[];
+  finishedAt: string;
+}
+
+// Closed and open topics alike: the rule reads the sub-issues, so a topic
+// finished moments ago (close-topics not yet run) releases now.
+const finished: Finished[] = [];
+for await (const raw of gh.list(`/repos/${gh.repo}/issues?labels=topic&state=all`)) {
+  const topic = readTopic(raw);
+  if (!topic) continue;
+  const problems = await readProblems(gh, topic.number);
+  const core = coreSet(problems);
+  if (core.finishedAt) finished.push({ topic, problems, core: core.all, finishedAt: core.finishedAt });
+}
+// Oldest first, so a backfill creates releases in campaign order.
+finished.sort((a, b) => a.finishedAt.localeCompare(b.finishedAt) || a.topic.number - b.topic.number);
+
+// ── existing releases ────────────────────────────────────────────
+
+/** Topic -> its release. Name and body are kept in sync with the render on every run. */
+const released = new Map<number, { id: number; tag: string; name: string; body: string }>();
+for await (const raw of gh.list(`/repos/${gh.repo}/releases`)) {
+  if (!raw || typeof raw !== "object") continue;
+  if (!("id" in raw) || typeof raw.id !== "number") continue;
+  if (!("tag_name" in raw) || typeof raw.tag_name !== "string") continue;
+  if (!("body" in raw) || typeof raw.body !== "string") continue;
+  const name = "name" in raw && typeof raw.name === "string" ? raw.name : "";
+  const m = raw.body.match(/<!-- release-topics: #(\d+) -->/);
+  if (m) released.set(Number(m[1]), { id: raw.id, tag: raw.tag_name, name, body: raw.body });
+}
+
+// ── timever ──────────────────────────────────────────────────────
+
+/**
+ * Timever of an instant. The API reports whole seconds, so SUBTIME is the
+ * tiebreak: two topics finishing in the same second (one push closing both
+ * last core problems) get consecutive nanoseconds, in (instant, topic) order.
+ */
+const tags = new Map<number, string>(); // topic -> tag
+{
+  let prev = "";
+  let ns = 0;
+  for (const f of finished) {
+    const iso = new Date(f.finishedAt).toISOString(); // 2026-09-24T18:36:38.000Z
+    const base = `${iso.slice(0, 10).replaceAll("-", "")}.${iso.slice(11, 19).replaceAll(":", "")}`;
+    ns = base === prev ? ns + 1 : Number(iso.slice(20, 23)) * 1_000_000;
+    prev = base;
+    tags.set(f.topic.number, `${base}.${String(ns).padStart(9, "0")}`);
+  }
+}
+
+// ── release body ─────────────────────────────────────────────────
+
+const ET_WHEN = new Intl.DateTimeFormat("en-US", {
+  timeZone: "America/New_York",
+  weekday: "short",
+  month: "short",
+  day: "numeric",
+  year: "numeric",
+  hour: "numeric",
+  minute: "2-digit",
+});
+const ET_DAY = new Intl.DateTimeFormat("en-US", {
+  timeZone: "America/New_York",
+  month: "short",
+  day: "numeric",
+});
+
+/** Topic body sections worth carrying into the changelog (skipped while still `TODO`). */
+const NOTES = ["Trigger", "Invariant", "Trap"] as const;
+
+function bodyField(body: string, field: string): string | undefined {
+  return body.match(new RegExp(`^\\*\\*${field}:\\*\\*\\s*(.+)$`, "m"))?.[1]?.trim();
+}
+
+function bodySection(body: string, heading: string): string | undefined {
+  const m = body.match(new RegExp(`^### ${heading}\\n([\\s\\S]*?)(?=^### |(?![\\s\\S]))`, "m"));
+  const text = m?.[1]?.trim();
+  return text && text !== "TODO" ? text : undefined;
+}
+
+function render(f: Finished, tag: string, sha: string, files: Map<number, string[]>): string {
+  const { topic, problems } = f;
+  const finishDay = etDate(new Date(f.finishedAt));
+  // Snapshot at the finish instant: a problem closed later was open then.
+  const closedBy = (p: Problem) => p.closedAt !== null && p.closedAt <= f.finishedAt;
+  const onDay = problems.filter((p) => closedBy(p) && etDate(new Date(p.closedAt!)) === finishDay);
+  const earlier = problems.filter((p) => closedBy(p) && etDate(new Date(p.closedAt!)) !== finishDay);
+  const open = problems.filter((p) => !closedBy(p));
+
+  const row = (p: Problem): string[] => {
+    const lc = Number(p.title.match(/^LC (\d+)/)?.[1]);
+    const code = closedBy(p)
+      ? (files.get(lc) ?? []).map(
+          (path) => `[${path.slice(path.lastIndexOf(".") + 1)}](https://github.com/${gh.repo}/blob/${tag}/${encodeURI(path)})`,
+        )
+      : [];
+    return [
+      `#${p.number}`,
+      p.title,
+      labelValue(p, "set:") ?? "—",
+      labelValue(p, "diff:") ?? "—",
+      closedBy(p) ? ET_DAY.format(new Date(p.closedAt!)) : "—",
+      code.length ? [...code, `[docs](${DOCS_SITE}/${lc})`].join(" · ") : "—",
+    ];
+  };
+  const table = (list: Problem[]) =>
+    markdownTable([["Issue", "Problem", "Set", "Difficulty", "Closed (ET)", "Solution"], ...list.map(row)]);
+
+  // Blume's changelog derives each page's meta description from the opening
+  // prose, stripping markdown and line breaks without adding a space — so lead
+  // with one self-contained sentence and keep the fields on one `·` line.
+  const when = ET_WHEN.format(new Date(f.finishedAt));
+  const summary =
+    `Finished ${when} ET: all ${f.core.length} core problems closed, ` +
+    `${onDay.length} ${onDay.length === 1 ? "problem" : "problems"} closed that day.`;
+  const fields: string[] = [];
+  const scheduled = bodyField(topic.body, "Scheduled");
+  if (scheduled) fields.push(`**Scheduled:** ${scheduled}`);
+  if (topic.milestone) fields.push(`**Phase:** ${topic.milestone}`);
+  fields.push(`**Topic:** #${topic.number}`);
+  const buildsOn = bodyField(topic.body, "Builds on");
+  if (buildsOn) fields.push(`**Builds on:** ${buildsOn}`);
+  // The marker is how a later run finds this release; see the file header.
+  const sections = [`<!-- release-topics: #${topic.number} -->\n${summary}`, fields.join(" · ")];
+  sections.push(`### Closed ${ET_DAY.format(new Date(f.finishedAt))} — the day the topic finished\n\n${table(onDay)}`);
+  if (earlier.length) sections.push(`### Closed earlier\n\n${table(earlier)}`);
+  if (open.length) sections.push(`### Open at release\n\n${table(open)}`);
+  const notes = NOTES.flatMap((h) => {
+    const text = bodySection(topic.body, h);
+    return text ? [`**${h}.** ${text}`] : [];
+  });
+  if (notes.length) sections.push(`### Notes\n\n${notes.join("\n\n")}`);
+  sections.push(
+    `---\n\n\`${tag}\` is [timever](${TIMEVER}) for the UTC instant the core set completed; ` +
+      `it tags ${sha.slice(0, 7)}, the last main commit before it.`,
+  );
+  return `${sections.join("\n\n")}\n`;
+}
+
+// ── reconcile ────────────────────────────────────────────────────
+
+const latest = finished.at(-1)?.topic.number;
+const report: string[][] = [];
+const previews: string[] = [];
+let created = 0;
+let updated = 0;
+
+for (const f of finished) {
+  const { topic } = f;
+  const finishedEt = etDate(new Date(f.finishedAt));
+  const existing = released.get(topic.number);
+  // An existing release keeps its tag and commit; only its name and body are
+  // reconciled. Its tag may postdate this clone (released by another run), so
+  // fetch it when missing — read-only, so a dry run does it too.
+  const tag = existing?.tag ?? tags.get(topic.number)!;
+  if (existing && Bun.spawnSync(["git", "rev-parse", "-q", "--verify", `refs/tags/${tag}`], { cwd: ROOT }).exitCode !== 0) {
+    git("fetch", "-q", "origin", `refs/tags/${tag}:refs/tags/${tag}`);
+  }
+  const sha = existing
+    ? git("rev-parse", `${tag}^{commit}`)
+    : git("rev-list", "-1", "--first-parent", `--before=${f.finishedAt}`, "HEAD");
+  if (!sha) {
+    report.push([`#${topic.number}`, topic.title, finishedEt, tag, "ERROR: no commit before finish"]);
+    continue;
+  }
+  // LC number -> its first-solve files in the tagged tree. Keyed by file name,
+  // like firstSolved(): tags before the bucket split see `work/<Difficulty>/…`,
+  // and the work/3 + work/7 re-solves are not the solve that closed the issue.
+  const files = new Map<number, string[]>();
+  for (const path of git("ls-tree", "-r", "--name-only", sha, "--", "work").split("\n")) {
+    const bucket = parseWorkPath(path.slice("work/".length))?.bucket;
+    const lc = path.match(/\/(\d+)\.[^/]+\.(?:js|py)$/)?.[1];
+    if (!lc || (bucket && bucket !== 1)) continue;
+    files.set(Number(lc), [...(files.get(Number(lc)) ?? []), path]);
+  }
+  const body = render(f, tag, sha, files);
+  const name = topic.title;
+
+  if (existing) {
+    if (existing.body === body && existing.name === name) {
+      report.push([`#${topic.number}`, topic.title, finishedEt, tag, "released"]);
+    } else if (DRY) {
+      previews.push(`## ${name} (${tag})\n\n${body}`);
+      report.push([`#${topic.number}`, topic.title, finishedEt, tag, "would update"]);
+    } else {
+      await gh.api(`/repos/${gh.repo}/releases/${existing.id}`, {
+        method: "PATCH",
+        body: JSON.stringify({ name, body }),
+      });
+      report.push([`#${topic.number}`, topic.title, finishedEt, tag, "updated"]);
+      updated++;
+    }
+    continue;
+  }
+
+  if (DRY) {
+    previews.push(`## ${name} (${tag})\n\n${body}`);
+    report.push([`#${topic.number}`, topic.title, finishedEt, tag, "would release"]);
+    continue;
+  }
+
+  const remote = git("ls-remote", "--tags", "origin", `refs/tags/${tag}`);
+  if (!remote) {
+    const local = Bun.spawnSync(["git", "rev-parse", "-q", "--verify", `refs/tags/${tag}`], { cwd: ROOT });
+    if (local.exitCode !== 0) {
+      const tagged = Bun.spawnSync(
+        ["git", "tag", "-a", tag, sha, "-m", `${topic.title} (#${topic.number})\n\nCore set complete: ${f.core.map((n) => `#${n}`).join(", ")}`],
+        { cwd: ROOT, env: { ...process.env, GIT_COMMITTER_DATE: f.finishedAt } },
+      );
+      if (tagged.exitCode !== 0) throw new Error(`git tag ${tag}: ${tagged.stderr.toString().trim()}`);
+    }
+    git("push", "origin", `refs/tags/${tag}`);
+  }
+  await gh.api(`/repos/${gh.repo}/releases`, {
+    method: "POST",
+    body: JSON.stringify({
+      tag_name: tag,
+      name,
+      body,
+      make_latest: topic.number === latest ? "true" : "false",
+    }),
+  });
+  report.push([`#${topic.number}`, topic.title, finishedEt, tag, "released now"]);
+  created++;
+}
+
+// ── report ───────────────────────────────────────────────────────
+
+if (previews.length) console.log(`${previews.join("\n")}\n`);
+const rows = [["topic", "title", "finished (ET)", "tag", "status"], ...report];
+printTable(rows);
+const would = (status: string) => report.filter((r) => r[4] === status).length;
+console.log(
+  `\n${finished.length} finished topics · ` +
+    (DRY
+      ? `would release ${would("would release")}, update ${would("would update")}`
+      : `released ${created}, updated ${updated}`),
+);
+
+await writeStepSummary(
+  `### release-topics${DRY ? " (dry run)" : ""}\n\n` +
+    `${finished.length} finished topics, ${released.size} already released.\n\n` +
+    (report.length ? `${markdownTable(rows)}\n` : "No finished topics.\n") +
+    (previews.length ? `\n${previews.join("\n")}` : ""),
+);

apps/cli/solutions.ts

@@ -30,17 +30,27 @@ function lcNumber(rel: string): number | undefined {
 }
 
 /** Fuzzy-pick a solution under work/ and run `leetcode <command>` on it. */
-export async function runOnSolution(command: "test" | "submit", message: string): Promise<never> {
+export async function runOnSolution(
+  command: "test" | "submit",
+  message: string,
+): Promise<never> {
   const db = problemDb();
 
-  const scanned = [...new Bun.Glob("**/*.{js,ts,py,java,c,cpp,go,rs,rb,swift,kt,cs}").scanSync({ cwd: WORK_DIR })];
+  const scanned = [
+    ...new Bun.Glob("**/*.{js,ts,py,java,c,cpp,go,rs,rb,swift,kt,cs}").scanSync(
+      { cwd: WORK_DIR },
+    ),
+  ];
 
   // register creation times so files older than the db still sort correctly
   for (const f of scanned) {
     const num = lcNumber(f);
     if (num === undefined) continue;
     const stat = statSync(join(WORK_DIR, f));
-    db.ensureSolution(num, new Date(stat.birthtimeMs || stat.mtimeMs).toISOString());
+    db.ensureSolution(
+      num,
+      new Date(stat.birthtimeMs || stat.mtimeMs).toISOString(),
+    );
   }
   const activity = db.solutionActivity();
 
@@ -51,8 +61,7 @@ export async function runOnSolution(command: "test" | "submit", message: string)
     return (command === "test" ? row?.lastTested : row?.createdAt) ?? undefined;
   };
 
-  const files = scanned
-    .sort((a, b) => {
+  const files = scanned.sort((a, b) => {
     const ka = sortKey(a);
     const kb = sortKey(b);
     if (ka !== kb) {
@@ -64,7 +73,9 @@ export async function runOnSolution(command: "test" | "submit", message: string)
   });
 
   if (files.length === 0) {
-    log.error(`No solution files found in ${relative(process.cwd(), WORK_DIR)}/`);
+    log.error(
+      `No solution files found in ${relative(process.cwd(), WORK_DIR)}/`,
+    );
     process.exit(1);
   }
 
@@ -74,11 +85,14 @@ export async function runOnSolution(command: "test" | "submit", message: string)
     maxItems: 12,
     options: files.map((f) => {
       const parsed = parseWorkPath(f);
-      const stage = parsed?.bucket === 1 ? "first solve" : `${parsed?.bucket}-day review`;
+      const stage =
+        parsed?.bucket === 1 ? "first solve" : `${parsed?.bucket}-day review`;
       return {
         value: f,
         label: basename(f),
-        hint: parsed ? `${stage} · ${parsed.difficulty} · ${parsed.category}` : f,
+        hint: parsed
+          ? `${stage} · ${parsed.difficulty} · ${parsed.category}`
+          : f,
       };
     }),
     filter: (search, option) => {

apps/cli/stats.ts

@@ -0,0 +1,458 @@
+#!/usr/bin/env bun
+/**
+ * `bun run stats` — the campaign dashboard, in the terminal.
+ *
+ * Four panes over ONE source: GET /api/stats. D1 owns SRS state, so this
+ * fetches the Worker's aggregate rather than recomputing anything from work/
+ * or from git — a second answer to "how far along am I" is exactly the drift
+ * the campaign is built to avoid. The one local fact shown is the work/ file
+ * inventory, which is inventory, not schedule. Unreachable Worker = an error,
+ * never a reconstructed guess.
+ *
+ * The panes:
+ *   Overview  campaign clock, solved counts, phase bars, recent activity
+ *   Ladder    the +3/+7 rungs and the 14-day due queue
+ *   Concepts  every topic by temperature — what has gone cold
+ *   Activity  the campaign heatmap and the weekly gates
+ *
+ * Outside a TTY (a pipe, CI) it prints every pane once and exits, so the same
+ * command works in a scrollback or a file.
+ */
+import {
+  fetchStats,
+  SRS_API,
+  STAGES,
+  TEMPERATURES,
+  type Stats,
+  type Temperature,
+  type Topic,
+} from "./api.ts";
+import {
+  BLUE,
+  FG,
+  GREEN,
+  GREENS,
+  LINE,
+  MUTED,
+  RED,
+  YELLOW,
+  bar,
+  bold,
+  cell,
+  fg,
+  heatCell,
+  openScreen,
+  padTo,
+  rule,
+  sparkline,
+  stackedBar,
+  width,
+} from "./tui.ts";
+import { BUCKETS, WINDOWS, solvedInBucket } from "./work.ts";
+
+// ── shared vocabulary → colour ───────────────────────────────────
+
+// Temperature is an action ramp, not a thermometer: green is warm enough to
+// leave alone, red is the concept that wants revisiting. The band names carry
+// the heat, the colours carry the urgency — and the glyphs carry both again,
+// so a piped or NO_COLOR dashboard still separates the bands.
+const TEMP_COLOR: Record<Temperature, string> = {
+  hot: GREENS[4]!,
+  fresh: GREEN,
+  fading: YELLOW,
+  cold: RED,
+};
+
+const TEMP_GLYPH: Record<Temperature, string> = {
+  hot: "█",
+  fresh: "▓",
+  fading: "▒",
+  cold: "░",
+};
+
+const DIFF_COLOR: Record<string, string> = { easy: GREEN, medium: YELLOW, hard: RED };
+
+const LABEL = 15; // left-hand label column, shared by every pane
+
+/** "2026-08-31" → "Mon 31", read as a plain calendar date, never localised. */
+function dayLabel(iso: string): string {
+  const [y, m, d] = iso.split("-").map(Number);
+  const weekday = new Date(Date.UTC(y!, m! - 1, d!)).getUTCDay();
+  return `${["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"][weekday]} ${String(d).padStart(2, "0")}`;
+}
+
+// ── overview ─────────────────────────────────────────────────────
+
+function overview(s: Stats, cols: number): string[] {
+  const bars = Math.max(10, Math.min(48, cols - LABEL - 18));
+  const lines: string[] = [];
+
+  const { day, days, week } = s.campaign;
+  lines.push(rule("campaign", cols));
+  lines.push(
+    `${cell("Day", LABEL)}${bar(day, days, bars)}  ${fg(FG, `${day}/${days}`)}` +
+      fg(MUTED, `  week ${week}`),
+  );
+  const streak = s.streak > 0 ? fg(GREENS[4]!, `${s.streak} day${s.streak === 1 ? "" : "s"}`) : fg(MUTED, "none");
+  lines.push(`${cell("Streak", LABEL)}${streak}`);
+
+  const total = s.difficulty.reduce((n, d) => n + d.total, 0);
+  const done = s.difficulty.reduce((n, d) => n + d.done, 0);
+  lines.push("");
+  lines.push(rule("solved", cols));
+  lines.push(
+    `${cell("All", LABEL)}${bar(done, total, bars)}  ${fg(FG, `${done}/${total}`)}` +
+      fg(MUTED, `  ${total > 0 ? Math.round((done / total) * 100) : 0}%`),
+  );
+  for (const d of s.difficulty) {
+    lines.push(
+      `${cell(d.difficulty, LABEL)}${bar(d.done, d.total, bars, DIFF_COLOR[d.difficulty] ?? GREEN)}` +
+        `  ${fg(MUTED, `${d.done}/${d.total}`)}`,
+    );
+  }
+
+  lines.push("");
+  lines.push(rule("phases", cols));
+  lines.push(
+    `${" ".repeat(LABEL)}${fg(GREEN, "█")} ${fg(MUTED, "core")}  ${fg(BLUE, "█")} ${fg(MUTED, "optional")}  ` +
+      `${fg(RED, "█")} ${fg(MUTED, "deferred")}  ${fg(LINE, "░")} ${fg(MUTED, "remaining")}`,
+  );
+  // Every phase bar is scaled to the LARGEST phase, not to itself: phases are
+  // not the same size, and equal-length bars would hide that.
+  const scale = Math.max(
+    1,
+    ...s.phases.map((p) => p.core_total + p.optional_total + p.deferred_total),
+  );
+  for (const p of s.phases) {
+    const phaseDone = p.core_done + p.optional_done + p.deferred_done;
+    const phaseTotal = p.core_total + p.optional_total + p.deferred_total;
+    const segments = [
+      { value: p.core_done, color: GREEN },
+      { value: p.optional_done, color: BLUE },
+      { value: p.deferred_done, color: RED },
+      { value: phaseTotal - phaseDone, color: LINE, glyph: "░" },
+    ];
+    lines.push(
+      `${cell(p.name, LABEL - 1)} ${stackedBar(segments, scale, bars)}  ${fg(MUTED, `${phaseDone}/${phaseTotal}`)}`,
+    );
+  }
+
+  lines.push("");
+  lines.push(rule("last 14 days", cols));
+  const window = s.heat.slice(Math.max(0, day - 14), day);
+  const attempts = window.reduce((n, h) => n + h.attempts, 0);
+  const passes = window.reduce((n, h) => n + h.passes, 0);
+  lines.push(
+    `${cell("Attempts", LABEL)}${sparkline(window.map((h) => h.attempts))}  ` +
+      fg(MUTED, `${attempts} attempts · ${passes} passed`),
+  );
+
+  // The one local fact on the dashboard: solutions on disk, per
+  // spaced-repetition bucket. Inventory, not schedule — D1's ladder is the
+  // schedule, and the Ladder pane is where it is shown. Empty scaffolds do not
+  // count, the same rule close-solved.ts closes issues by.
+  lines.push("");
+  lines.push(rule("work/ on disk", cols));
+  lines.push(
+    cell("Solutions", LABEL) +
+      BUCKETS.map((b) => `${fg(FG, String(solvedInBucket(b)))} ${fg(MUTED, `in work/${b}`)}`).join(
+        fg(MUTED, " · "),
+      ),
+  );
+
+  return lines;
+}
+
+// ── ladder ───────────────────────────────────────────────────────
+
+function ladder(s: Stats, cols: number): string[] {
+  const bars = Math.max(10, Math.min(48, cols - LABEL - 18));
+  const lines: string[] = [rule("ladder", cols)];
+  lines.push(fg(MUTED, `${" ".repeat(LABEL)}the review each problem owes next`));
+
+  const rungs = STAGES.map((stage) => s.ladder[stage] ?? 0);
+  const peak = Math.max(1, ...rungs);
+  STAGES.forEach((stage, i) => {
+    const n = rungs[i]!;
+    // new is the untouched pile and retired is the finished one; only the
+    // middle rungs are live work, so only they get the live colour.
+    const color = stage === "new" ? LINE : stage === "retired" ? GREENS[4]! : GREEN;
+    lines.push(`${cell(stage, LABEL)}${bar(n, peak, bars, color)}  ${fg(FG, String(n))}`);
+  });
+
+  lines.push("");
+  lines.push(rule("due queue", cols));
+  const today = s.queue[0];
+  lines.push(
+    fg(MUTED, `${" ".repeat(LABEL)}cumulative: everything the ladder wants by that day`) +
+      (today ? fg(FG, `  ·  ${today.due} due today`) : ""),
+  );
+  const depth = Math.max(1, ...s.queue.map((q) => q.due));
+  for (const q of s.queue) {
+    const color = q.due > 3 ? RED : q.due > 0 ? GREEN : LINE;
+    lines.push(
+      `${cell(dayLabel(q.date), LABEL)}${bar(q.due, depth, bars, color)}  ${fg(MUTED, String(q.due))}`,
+    );
+  }
+
+  return lines;
+}
+
+// ── concepts ─────────────────────────────────────────────────────
+
+/** Coldest first, and everything the schedule has not reached yet last. */
+function byUrgency(a: Topic, b: Topic): number {
+  if (a.taught !== b.taught) return a.taught ? -1 : 1;
+  return (
+    TEMPERATURES.indexOf(b.temperature) - TEMPERATURES.indexOf(a.temperature) ||
+    (b.age ?? Infinity) - (a.age ?? Infinity) ||
+    a.issue - b.issue
+  );
+}
+
+// Row layout: "● " + name + temp + coverage bar + done/total + last + due.
+// Everything but the name is fixed, so the name absorbs the terminal width.
+const TEMP_W = 7;
+const COVER_W = 10;
+const COUNT_W = 6;
+const AGE_W = 6;
+const DUE_W = 3;
+const CONCEPT_FIXED = 3 + (TEMP_W + 1) + (COVER_W + 1) + (COUNT_W + 1) + (AGE_W + 1) + DUE_W + 1;
+
+function concepts(s: Stats, cols: number): string[] {
+  const lines: string[] = [rule("concepts by temperature", cols)];
+  // Thresholds are the ladder's windows; print them rather than restate them.
+  const bands: [Temperature, string][] = [
+    ["hot", `≤${WINDOWS[0]}d`],
+    ["fresh", `≤${WINDOWS[1]}d`],
+    ["fading", `≤${WINDOWS[1] * 2}d`],
+    ["cold", "older, or never"],
+  ];
+  lines.push(
+    fg(MUTED, "  last exercised — ") +
+      bands
+        .map(([t, when]) => `${fg(TEMP_COLOR[t], `${TEMP_GLYPH[t]} ${t}`)} ${fg(MUTED, when)}`)
+        .join(fg(MUTED, " · ")),
+  );
+
+  const taught = s.topics.filter((t) => t.taught);
+  const counts = TEMPERATURES.map((t) => ({
+    value: taught.filter((x) => x.temperature === t).length,
+    color: TEMP_COLOR[t],
+    glyph: TEMP_GLYPH[t],
+  }));
+  lines.push("");
+  lines.push(`  ${stackedBar(counts, Math.max(1, taught.length), Math.max(10, Math.min(60, cols - 4)))}`);
+  lines.push(
+    `  ${TEMPERATURES.map((t, i) => `${fg(TEMP_COLOR[t], TEMP_GLYPH[t])} ${counts[i]!.value} ${fg(MUTED, t)}`).join("  ")}` +
+      fg(MUTED, `   of ${taught.length} taught so far`),
+  );
+
+  const nameW = Math.max(12, Math.min(34, cols - CONCEPT_FIXED));
+  lines.push("");
+  lines.push(
+    fg(
+      MUTED,
+      `   ${cell("concept", nameW)} ${cell("temp", TEMP_W)} ` +
+        `${cell("coverage", COVER_W + 1 + COUNT_W)} ${cell("last", AGE_W)} ${cell("due", DUE_W, "right")}`,
+    ),
+  );
+
+  for (const t of s.topics.slice().sort(byUrgency)) {
+    // An unreached concept has no temperature to report — it shows the week
+    // the schedule gets to it instead, so the list stays one list.
+    const color = t.taught ? TEMP_COLOR[t.temperature] : LINE;
+    const age =
+      !t.taught ? "—" : t.age === null ? "never" : t.age <= 0 ? "today" : `${t.age}d`;
+    lines.push(
+      ` ${fg(color, t.taught ? TEMP_GLYPH[t.temperature] : "·")} ${fg(t.taught ? FG : MUTED, cell(t.name, nameW))} ` +
+        `${fg(color, cell(t.taught ? t.temperature : `wk ${t.week ?? "?"}`, TEMP_W))} ` +
+        `${bar(t.done, t.total, COVER_W, t.taught ? GREEN : LINE)} ` +
+        `${fg(MUTED, cell(`${t.done}/${t.total}`, COUNT_W))} ${fg(MUTED, cell(age, AGE_W))} ` +
+        `${t.due > 0 ? fg(GREEN, cell(String(t.due), DUE_W, "right")) : fg(LINE, cell("·", DUE_W, "right"))}`,
+    );
+  }
+
+  return lines;
+}
+
+// ── activity ─────────────────────────────────────────────────────
+
+const WEEKDAYS = ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"];
+
+function activity(s: Stats, cols: number): string[] {
+  const lines: string[] = [rule("attempts per campaign day", cols)];
+  lines.push(fg(MUTED, "  the README heatmap, same ramp — Sunday is the rest day"));
+  lines.push("");
+
+  // CAMPAIGN_START is a Monday, so the grid is simply the series in weeks of
+  // seven: column = week, row = weekday, exactly as the SVG lays it out.
+  const weeks = Math.ceil(s.heat.length / 7);
+  lines.push(
+    `      ${fg(MUTED, Array.from({ length: weeks }, (_, w) => ` ${String(w + 1).padStart(2)}`).join(""))}`,
+  );
+  WEEKDAYS.forEach((name, row) => {
+    const cells = Array.from({ length: weeks }, (_, w) => {
+      const entry = s.heat[w * 7 + row];
+      if (entry === undefined) return "   ";
+      // The marker sits in the gutter, not inside the cell: a foreground
+      // escape within a background run would end the background early.
+      const marker = s.campaign.day - 1 === w * 7 + row ? fg(FG, "▸") : " ";
+      return marker + heatCell(entry.attempts, "  ");
+    }).join("");
+    lines.push(`  ${fg(MUTED, cell(name, 4))}${cells}`);
+  });
+  lines.push("");
+  lines.push(
+    `  ${fg(MUTED, "less ")}${GREENS.map((_, level) => heatCell(level, "  ")).join("")}${fg(MUTED, " more")}` +
+      fg(MUTED, "   · one cell per day, colour = attempts, ▸ marks today"),
+  );
+
+  lines.push("");
+  lines.push(rule("weekly gates", cols));
+  if (s.gates.length === 0) {
+    lines.push(fg(MUTED, "  no gate has been scored yet"));
+  }
+  const gateW = Math.max(10, Math.min(24, cols - 30));
+  for (const g of s.gates) {
+    // Gates were stored as an integer percent before they were stored as a
+    // fraction; both are in the table, so normalise on read.
+    const rate = g.pass_rate === null ? null : g.pass_rate <= 1 ? g.pass_rate : g.pass_rate / 100;
+    const color = rate === null ? LINE : rate >= 0.7 ? GREEN : RED;
+    lines.push(
+      `  ${fg(FG, cell(`Week ${g.week}`, 9))}` +
+        `${bar(rate ?? 0, 1, gateW, color)}` +
+        `  ${fg(color, cell(rate === null ? "open" : `${Math.round(rate * 100)}%`, 5))}` +
+        `  ${fg(MUTED, g.issue === null ? "" : `#${g.issue}`)}${fg(MUTED, g.closed_on ? `  closed ${g.closed_on}` : "")}`,
+    );
+  }
+
+  return lines;
+}
+
+// ── panes ────────────────────────────────────────────────────────
+
+const PANES: { name: string; render: (s: Stats, cols: number) => string[] }[] = [
+  { name: "Overview", render: overview },
+  { name: "Ladder", render: ladder },
+  { name: "Concepts", render: concepts },
+  { name: "Activity", render: activity },
+];
+
+// ── non-interactive: every pane, once ────────────────────────────
+
+let stats: Stats;
+try {
+  stats = await fetchStats();
+} catch (err) {
+  console.error(`stats: ${err instanceof Error ? err.message : String(err)}`);
+  console.error(`stats: D1 is the only source of SRS truth — nothing to fall back to (SRS_API=${SRS_API}).`);
+  process.exit(1);
+}
+
+if (!process.stdout.isTTY) {
+  const cols = 80;
+  for (const pane of PANES) {
+    console.log(bold(pane.name.toUpperCase()));
+    for (const line of pane.render(stats, cols)) console.log(line);
+    console.log("");
+  }
+  process.exit(0);
+}
+
+// ── interactive ──────────────────────────────────────────────────
+
+let pane = 0;
+let offset = 0;
+let note = "";
+
+// Quitting resolves this; the finally below is what restores the terminal, so
+// a thrown render never leaves the shell in raw mode on the alternate screen.
+const { promise: quit, resolve: leave } = Promise.withResolvers<void>();
+const screen = openScreen(onKey, draw);
+
+function frame(): string[] {
+  const cols = screen.columns;
+  const tabs = PANES.map((p, i) =>
+    i === pane ? bold(fg(FG, ` ${p.name} `)) : fg(MUTED, ` ${p.name} `),
+  ).join(fg(LINE, "│"));
+  const clock = fg(MUTED, `day ${stats.campaign.day}/${stats.campaign.days} · streak ${stats.streak}  `);
+  const header = padTo(tabs, Math.max(0, cols - width(clock))) + clock;
+
+  // header + rule + body + footer fills the terminal exactly.
+  const body = PANES[pane]!.render(stats, cols);
+  const height = Math.max(1, screen.rows - 3);
+  offset = Math.max(0, Math.min(offset, Math.max(0, body.length - height)));
+  const scrolled =
+    body.length > height ? ` · ${offset + 1}-${Math.min(offset + height, body.length)}/${body.length}` : "";
+
+  return [
+    header,
+    fg(LINE, "─".repeat(cols)),
+    ...body.slice(offset, offset + height),
+    fg(MUTED, `Tab/←→ pane · ↑↓ scroll · r refresh · q quit${scrolled}`) + (note ? `  ${fg(YELLOW, note)}` : ""),
+  ];
+}
+
+function draw(): void {
+  screen.draw(frame());
+}
+
+function onKey(chunk: string): void {
+  switch (chunk) {
+    // Raw mode delivers Ctrl-C as a byte, not a signal, so it is handled here.
+    case "q":
+    case "\x03":
+    case "\x1b":
+      leave();
+      return;
+    case "\t":
+    case "\x1b[C":
+    case "l":
+      pane = (pane + 1) % PANES.length;
+      offset = 0;
+      break;
+    case "\x1b[Z":
+    case "\x1b[D":
+    case "h":
+      pane = (pane + PANES.length - 1) % PANES.length;
+      offset = 0;
+      break;
+    case "\x1b[A":
+    case "k":
+      offset = Math.max(0, offset - 1);
+      break;
+    case "\x1b[B":
+    case "j":
+      offset += 1;
+      break;
+    case "r":
+      note = "refreshing…";
+      draw();
+      void fetchStats()
+        .then((fresh) => {
+          stats = fresh;
+          note = "";
+        })
+        .catch((err: unknown) => {
+          note = `refresh failed: ${err instanceof Error ? err.message : String(err)}`;
+        })
+        .finally(draw);
+      return;
+    default:
+      if (chunk >= "1" && chunk <= String(PANES.length)) {
+        pane = Number(chunk) - 1;
+        offset = 0;
+        break;
+      }
+      return;
+  }
+  draw();
+}
+
+try {
+  draw();
+  await quit;
+} finally {
+  screen.close();
+}

apps/cli/sync.ts

@@ -2,24 +2,69 @@
 /**
  * Sync work/1 leetcode solutions into apps/docs/content/ pages.
  *
- * - New problems get a full page (frontmatter, badge, warning, examples,
+ * - New problems get a full page (frontmatter, warning, examples,
  *   constraints, solution) in the gold-standard format.
- * - Already-ported pages only get their `## Solution` section regenerated,
- *   so hand-curated prose is never touched.
+ * - Already-ported pages only get their script-owned parts regenerated — the
+ *   frontmatter `icon:` (`PAGE_ICON`) and the `## Solution` section — so
+ *   hand-curated prose is never touched.
  * - When a problem is solved in both JavaScript and Python the solution
  *   renders as a <CodeGroup> (Python first); single-language solutions
  *   render as a plain fence.
+ * - Every page carries LeetCode's own topic tags as frontmatter `topics:`
+ *   (`{ name, slug }` per tag, LeetCode's order), fetched from the GraphQL
+ *   `topicTags` once — when the page is created, or on any later run that
+ *   finds the key missing — and never refreshed after, so a sync with nothing
+ *   new makes no request. Delete the key to refetch it. The page itself
+ *   renders no badges: the docs MDX `wrapper`
+ *   (`apps/docs/components/ProblemBadges.astro`) turns `topics:` and the
+ *   `video:` key `videos.ts` writes into the badge row under the description.
+ * - Every tag a page carries that no campaign topic teaches (not a key of
+ *   `apps/docs/topic-landings.ts`) gets a placeholder guide page,
+ *   `guides/<slug>.mdx`, with `list:` pointing at LeetCode's problem list for
+ *   the tag. Created once (a missing or empty file), then hand-owned except
+ *   for `sidebar.badge`, which sync keeps at the guide's backlink count (the
+ *   problem pages carrying the tag; dropped at zero); the tag's badge on a
+ *   problem page links to it. A guide may be filed into a category `(group)`
+ *   folder (e.g. `guides/(2-algorithms)/`) — no route segment, so
+ *   `/guides/<slug>` holds — and is found there by slug; a new placeholder
+ *   lands at the `guides/` root for a human to file (and give an `icon:`,
+ *   which every badge linking to the guide shows; sync warns while one is
+ *   missing or shared).
+ *
+ * The sidebar group is the campaign TOPIC from the README table (`tree-dfs/`,
+ * ordered by topic number via a script-owned `meta.ts`). A problem outside the
+ * plan (warm-ups) has no topic, so it groups under the data-structure CATEGORY
+ * its file sits under in `work/1/<Difficulty>/<Category>/` instead.
+ *
+ * Topics nest under their README PHASE: `(01-linear-structures)/tree-dfs/`.
+ * The phase folder is a Blume `(group)` — a sidebar section adding no route
+ * segment — while the topic folder is a real segment
+ * (`/tree-dfs/invert-binary-tree`), so a hand-written `index.mdx` in it is the
+ * topic's landing page at `/tree-dfs` and Blume links the sidebar group row to
+ * it. Sync never writes or moves an `index.mdx`, and never removes a folder
+ * that still holds one. A phase folder's `meta.ts` is written once, when
+ * missing, then hand-owned (its title is yours to rename); a topic's is
+ * script-owned. An unplanned category group has no phase and sits at the
+ * content root.
  *
  * Only the first-solve bucket is read: work/3 and work/7 hold blind re-solves
  * of problems whose page already exists (see work.ts), and a fresh scaffold
  * there would otherwise wipe the page's `## Solution`.
+ *
+ * Every page also gets a short link: `/<num>` → `/<topic>/<slug>` (so
+ * `/leetcode/217` opens Contains Duplicate). The rules live in the generated
+ * `apps/docs/redirects.ts`, which `blume.config.ts` imports — Blume takes exact
+ * root-relative paths and prepends the deployment base itself.
  */
-import { mkdir, rename } from "node:fs/promises";
-import { basename, join } from "node:path";
+import { mkdir, readdir, rename, rmdir, unlink } from "node:fs/promises";
+import { basename, dirname, join } from "node:path";
+
+import { TOPIC_LANDINGS } from "../docs/topic-landings.ts";
 
 const ROOT = join(import.meta.dir, "..", "..");
 const WORK = join(ROOT, "work", "1");
 const DOCS = join(ROOT, "apps", "docs", "content");
+const REDIRECTS = join(ROOT, "apps", "docs", "redirects.ts");
 
 type Lang = "js" | "py";
 
@@ -158,24 +203,246 @@ function parseHeader(header: string): Header {
 
 // ── README topic map ─────────────────────────────────────────────
 
+/** A campaign phase: `## Phase N — Name · Weeks …` in the README. */
+interface Phase {
+  order: number;
+  name: string;
+}
+
+/** A campaign topic: `<strong>NN. Name</strong>` in the README table. */
+interface Topic {
+  order?: number; // README topic number; absent for an unplanned problem's category group
+  name: string;
+  phase?: Phase; // absent for an unplanned category group
+}
+
+/** README phase names → the short labels the overview page uses. */
+const PHASE_ALIASES: Record<string, string> = {
+  "Nodal & Grid Structures": "Nodal & Grid",
+  "Hierarchical Structures": "Hierarchical",
+  "Relational Structures": "Relational",
+  "Decision-Space Exploration": "Decision Space",
+};
+
+const ROMAN = ["I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX", "X"];
+
 const TOPIC_ALIASES: Record<string, string> = {
   "Hash-Based Lookup": "Hash Table",
 };
 
-async function readmeTopics(): Promise<Map<number, string>> {
+/**
+ * Sidebar icon per group, keyed by the (post-alias) topic name — the same key an
+ * unplanned problem's category group uses, so `Stack` the category and `Stack`
+ * the topic share one row. Lucide names; Blume resolves them at build time and
+ * reports a diagnostic for a typo, but an unmapped group is caught here first.
+ */
+const TOPIC_ICONS: Record<string, string> = {
+  // README topics, in curriculum order
+  "Hash Table": "hash",
+  "Prefix Sum": "sigma",
+  "Two Pointers": "arrow-left-right",
+  "Sliding Window": "app-window",
+  "Binary Search": "search",
+  Stack: "layers",
+  "Monotonic Stack": "trending-up",
+  "Linked List": "link",
+  "Hybrid Structures": "combine",
+  "Matrix Index Math": "grid-3x3",
+  "Tree DFS": "folder-tree",
+  "Tree BFS": "network",
+  "Binary Search Tree": "git-fork",
+  "Heap / Priority Queue": "triangle",
+  Trie: "spell-check",
+  "Graph DFS": "waypoints",
+  "Graph BFS": "radar",
+  "Topological Sort": "workflow",
+  "Union-Find": "merge",
+  Backtracking: "undo-2",
+  "1-D Dynamic Programming": "columns-3",
+  "Multi-D / Grid DP": "table",
+  Greedy: "coins",
+  Intervals: "calendar-range",
+  // work/1 categories that can surface as an unplanned group
+  Array: "brackets",
+  String: "type",
+  Tree: "network",
+  "Depth-First Search": "folder-tree",
+};
+
+/** LC number -> topic. A problem listed under two topics keeps the first. */
+async function readmeTopics(): Promise<Map<number, Topic>> {
   const md = await Bun.file(join(ROOT, "README.md")).text();
-  const map = new Map<number, string>();
-  let topic = "";
+  const map = new Map<number, Topic>();
+  let phase: Phase | undefined;
+  let topic: Topic | null = null;
   for (const line of md.split("\n")) {
-    const t = line.match(/<strong>\d+\.\s*([^<]+)<\/strong>/);
-    if (t) topic = TOPIC_ALIASES[t[1]!.trim()] ?? t[1]!.trim();
+    const p = line.match(/^## Phase ([IVX]+) — (.+?) · /);
+    if (p) {
+      const name = p[2]!.replaceAll("&amp;", "&");
+      phase = { order: ROMAN.indexOf(p[1]!) + 1, name: PHASE_ALIASES[name] ?? name };
+    }
+    const t = line.match(/<strong>(\d+)\.\s*([^<]+)<\/strong>/);
+    if (t) topic = { order: Number(t[1]), name: TOPIC_ALIASES[t[2]!.trim()] ?? t[2]!.trim(), phase };
     if (!topic) continue;
     const n = line.match(/<td align="center">(\d+)<\/td>/);
-    if (n) map.set(Number(n[1]), topic);
+    if (n && !map.has(Number(n[1]))) map.set(Number(n[1]), topic);
   }
   return map;
 }
 
+/**
+ * Folder slug for a topic or phase name. Blume reads a leading `<digits>-` on a
+ * folder as a sidebar-order prefix and strips it from the route (`1-d-…` →
+ * `/d-…`), so a slug that would start that way keeps the digits glued to the
+ * next token (`1d-dynamic-programming`).
+ */
+function slugify(name: string): string {
+  return name
+    .toLowerCase()
+    .replace(/[^a-z0-9]+/g, "-")
+    .replace(/^-|-$/g, "")
+    .replace(/^(\d+)-/, "$1");
+}
+
+/**
+ * Content folder for a topic, relative to `DOCS`: `(0N-<phase>)/<topic>` for a
+ * planned topic (the phase is a `(group)`, so the route is still `/<topic>`),
+ * bare `<topic>` for an unplanned category group.
+ */
+function topicDir(topic: Topic): string {
+  const slug = slugify(topic.name);
+  return topic.phase ? `${phaseDir(topic.phase)}/${slug}` : slug;
+}
+
+function phaseDir(phase: Phase): string {
+  return `(${String(phase.order).padStart(2, "0")}-${slugify(phase.name)})`;
+}
+
+/**
+ * Blume `(group)` meta for a phase: the overview page's heading, in phase
+ * order. Written only when the folder has none — the title is hand-owned after
+ * that. Nothing is lost by never rewriting it: the order and name it is built
+ * from are also the folder name (`phaseDir`), so a README change to either
+ * lands in a new folder that gets a fresh meta.
+ */
+function phaseMeta(phase: Phase): string {
+  return `import { defineMeta } from "blume";\n\nexport default defineMeta({ title: ${JSON.stringify(`Phase ${phase.order}: ${phase.name}`)}, order: ${phase.order} });\n`;
+}
+
+/**
+ * Blume folder meta for a topic: exact label (the folder slug loses `/` and
+ * case), curriculum order, the sidebar icon, and `display: "group"` so the
+ * topic collapses under its phase heading. An unplanned category group
+ * (warm-ups) has no README number and sorts at 0, ahead of phase 1, so the
+ * sidebar opens on the basics.
+ */
+function groupMeta(topic: Topic): string {
+  const icon = TOPIC_ICONS[topic.name];
+  if (!icon) console.warn(`no icon for group ${JSON.stringify(topic.name)}: add it to TOPIC_ICONS`);
+  const fields = [`title: ${JSON.stringify(topic.name)}`, `order: ${topic.order ?? 0}`];
+  if (icon) fields.push(`icon: ${JSON.stringify(icon)}`);
+  fields.push(`display: "group"`);
+  return `import { defineMeta } from "blume";\n\nexport default defineMeta({ ${fields.join(", ")} });\n`;
+}
+
+// ── LeetCode topic tags ──────────────────────────────────────────
+
+/** One of LeetCode's topic tags. `slug` is not derivable from `name` (`Graph Theory` → `graph`). */
+interface TopicTag {
+  name: string;
+  slug: string;
+}
+
+/**
+ * The problem's topic tags, in LeetCode's order — or undefined, warned, when
+ * LeetCode cannot answer (offline commit, unknown slug): the page is written
+ * without `topics:` and the next sync fills it in.
+ */
+async function fetchTopicTags(sol: Solution): Promise<TopicTag[] | undefined> {
+  try {
+    const res = await fetch("https://leetcode.com/graphql", {
+      method: "POST",
+      headers: {
+        "content-type": "application/json",
+        "user-agent": "Mozilla/5.0",
+        referer: `https://leetcode.com/problems/${sol.slug}/`,
+      },
+      body: JSON.stringify({
+        query: "query topicTags($titleSlug: String!) { question(titleSlug: $titleSlug) { topicTags { name slug } } }",
+        variables: { titleSlug: sol.slug },
+      }),
+    });
+    if (!res.ok) throw new Error(`POST /graphql -> ${res.status} ${res.statusText}`);
+    const data = (await res.json()) as { data?: { question?: { topicTags?: TopicTag[] } | null } };
+    const tags = data.data?.question?.topicTags;
+    if (!Array.isArray(tags)) throw new Error("POST /graphql -> no such question");
+    return tags.map(({ name, slug }) => ({ name, slug }));
+  } catch (err) {
+    console.warn(`no topics for ${sol.num}.${sol.slug}: ${err instanceof Error ? err.message : err}`);
+    return undefined;
+  }
+}
+
+/** The frontmatter `topics:` block, one flow mapping per tag (JSON strings are valid YAML). */
+function topicsYaml(tags: TopicTag[]): string {
+  if (tags.length === 0) return "topics: []";
+  return ["topics:", ...tags.map((t) => `  - { name: ${JSON.stringify(t.name)}, slug: ${JSON.stringify(t.slug)} }`)].join("\n");
+}
+
+/** The frontmatter's `topics:` as sync wrote them (or a human edited them); [] when absent. */
+function frontmatterTopics(page: string): TopicTag[] {
+  const fm = page.match(/^---\n([\s\S]*?)\n---/)?.[1];
+  const data: unknown = fm ? Bun.YAML.parse(fm) : undefined;
+  if (!data || typeof data !== "object" || !("topics" in data) || !Array.isArray(data.topics)) return [];
+  return data.topics.filter((t): t is TopicTag => typeof t?.name === "string" && typeof t?.slug === "string");
+}
+
+// ── guides ───────────────────────────────────────────────────────
+
+/**
+ * Placeholder for a tag no campaign topic teaches: the `/guides/<slug>` page a
+ * problem's topic badge links to. `list:` is the tag's LeetCode problem list,
+ * rendered as a badge by the docs MDX `wrapper`. Written once — the page
+ * is hand-owned from then on.
+ */
+function guidePage(tag: TopicTag): string {
+  return [
+    "---",
+    `title: ${JSON.stringify(tag.name)}`,
+    `list: ${JSON.stringify(`https://leetcode.com/problem-list/${tag.slug}/`)}`,
+    "---",
+    "",
+    ":::note",
+    `This guide has not been written yet. The LeetCode list above has every problem tagged ${tag.name}.`,
+    ":::",
+    "",
+  ].join("\n");
+}
+
+/** Folder meta for `guides/`: its own header tab (`navigation.tabs` in blume.config.ts), so only the label. */
+const GUIDES_META = `import { defineMeta } from "blume";\n\nexport default defineMeta({ title: "Guides" });\n`;
+
+/**
+ * A guide's frontmatter with `sidebar.badge` set to its backlink count — the
+ * one key sync owns on a hand-owned guide — or dropped (with a `sidebar:` left
+ * empty) at zero, so the sidebar shows a count only where there is something
+ * to count.
+ */
+function withBacklinkBadge(page: string, count: number): string {
+  const fm = page.match(/^---\n[\s\S]*?\n---/);
+  if (!fm) return page;
+  let head = fm[0].replace(/^ {2}badge: .*\n/m, "");
+  if (count > 0) {
+    const line = `  badge: '${count}'`;
+    head = /^sidebar:$/m.test(head)
+      ? head.replace(/^sidebar:$/m, `sidebar:\n${line}`)
+      : head.replace(/\n---$/, `\nsidebar:\n${line}\n---`);
+  } else {
+    head = head.replace(/^sidebar:\n(?! {2})/m, "");
+  }
+  return head + page.slice(fm[0].length);
+}
+
 // ── inline-code formatting heuristics ────────────────────────────
 
 /** Identifiers worth backticking in prose, harvested from the code. */
@@ -277,7 +544,10 @@ function warningText(h: Header): string {
   );
 }
 
-function renderPage(sol: Solution, topic: string): string {
+/** Sidebar/page icon for every problem page (Lucide, resolved by Blume). */
+const PAGE_ICON = "dot";
+
+function renderPage(sol: Solution, tags: TopicTag[] | undefined): string {
   const h = sol.header;
   const ids = identifiers(sol);
   const description = h.statement[0]?.replace(/\.\s*$/, "") ?? "";
@@ -287,13 +557,13 @@ function renderPage(sol: Solution, topic: string): string {
     "---",
     `title: '${h.num}. ${h.title.replaceAll("'", "''")}'`,
     /[:#]/.test(description) ? `description: '${description.replaceAll("'", "''")}'` : `description: ${description}`,
+    `icon: ${PAGE_ICON}`,
+    ...(tags ? [topicsYaml(tags)] : []),
     "sidebar:",
     `  label: '${h.title.replaceAll("'", "''")}'`,
     `  badge: '${h.difficulty}'`,
     "---",
     "",
-    `<Badge variant="accent">${topic}</Badge>`,
-    "",
   );
 
   const warning = warningText(h);
@@ -350,6 +620,11 @@ for await (const rel of new Bun.Glob("**/*.{js,py}").scan(WORK)) {
 }
 
 const topics = await readmeTopics();
+// An unplanned problem whose work/ category is also a README topic name (a
+// `Hash Table` warm-up) files under that topic, in its phase, not a second
+// root-level `hash-table/`.
+const topicByName = new Map<string, Topic>();
+for (const topic of topics.values()) topicByName.set(topic.name, topic);
 
 /** Insert a number-free `sidebar.label` into existing frontmatter when missing. */
 function ensureLabel(page: string, h: Header): string {
@@ -359,6 +634,44 @@ function ensureLabel(page: string, h: Header): string {
   return page.replace(/^sidebar:$/m, `sidebar:\n${label}`);
 }
 
+/** Set the frontmatter's top-level `icon:` to `PAGE_ICON`, inserting it before `sidebar:`. */
+function ensureIcon(page: string): string {
+  const fm = page.match(/^---\n[\s\S]*?\n---/);
+  if (!fm) return page;
+  const line = `icon: ${PAGE_ICON}`;
+  const next = /^icon: .*$/m.test(fm[0])
+    ? fm[0].replace(/^icon: .*$/m, line)
+    : fm[0].replace(/^sidebar:$/m, `${line}\nsidebar:`);
+  return next + page.slice(fm[0].length);
+}
+
+/** Insert `topics:` before `sidebar:` when the frontmatter lacks it; an existing list is kept as is. */
+async function ensureTopics(page: string, sol: Solution): Promise<string> {
+  const fm = page.match(/^---\n[\s\S]*?\n---/);
+  if (!fm || /^topics:/m.test(fm[0])) return page;
+  const tags = await fetchTopicTags(sol);
+  if (!tags) return page;
+  return fm[0].replace(/^sidebar:$/m, `${topicsYaml(tags)}\nsidebar:`) + page.slice(fm[0].length);
+}
+
+/**
+ * Offset just past the script-owned `## Solution` section: the next top-level
+ * heading that is not inside a code fence, or end of file. Sections a human
+ * appends after the solution survive regeneration.
+ */
+function solutionEnd(page: string, from: number): number {
+  const lines = page.slice(from).split("\n");
+  let offset = from + lines[0]!.length + 1; // past the '## Solution' line itself
+  let fenced = false;
+  for (let i = 1; i < lines.length; i++) {
+    const line = lines[i]!;
+    if (line.startsWith("```")) fenced = !fenced;
+    else if (!fenced && line.startsWith("## ")) return offset;
+    offset += line.length + 1;
+  }
+  return page.length;
+}
+
 // Existing docs pages, keyed by leetcode number from the frontmatter title.
 const pages = new Map<number, string>(); // num -> path relative to DOCS
 for (const rel of (await Array.fromAsync(new Bun.Glob("**/*.mdx").scan(DOCS))).sort()) {
@@ -369,16 +682,28 @@ for (const rel of (await Array.fromAsync(new Bun.Glob("**/*.mdx").scan(DOCS))).s
 
 const report: [string, string, string][] = [];
 const ordered = [...solutions.values()].sort((a, b) => a.num - b.num);
+const groups = new Map<string, Topic>(); // topic folder -> topic, for meta.ts
+const phases = new Map<string, Phase>(); // phase folder -> phase, for meta.ts
+const vacated = new Set<string>(); // folders a page moved out of; removed below if empty
+const redirects: string[] = []; // `{ from: "/<num>", to: "/<topic>/<slug>" }` rows, numeric order
+const tags = new Map<string, TopicTag>(); // every tag slug any problem page carries -> tag
+const tagged = new Map<string, number>(); // tag slug -> how many problem pages carry it
 
 for (const sol of ordered) {
   const langs = Object.keys(sol.code).sort().join("+");
   const workRef = `${sol.num}.${sol.slug} (${langs})`;
-  // (category) group folder + leetcode-number prefix: numeric sidebar order, both stripped from the URL.
-  const group = `(${sol.category.toLowerCase().replaceAll(" ", "-")})`;
-  const name = `${group}/${sol.num}-${sol.slug}.mdx`;
+  // (0N-<phase>)/<topic>/ folder (the topic is a real route segment, so its
+  // index.mdx is the landing page) + leetcode-number prefix: numeric sidebar
+  // order, prefix stripped from the URL.
+  const topic = topics.get(sol.num) ?? topicByName.get(sol.category) ?? { name: sol.category };
+  const dir = topicDir(topic);
+  groups.set(dir, topic);
+  if (topic.phase) phases.set(phaseDir(topic.phase), topic.phase);
+  const name = `${dir}/${sol.num}-${sol.slug}.mdx`;
   const existing = pages.get(sol.num);
-  await mkdir(join(DOCS, group), { recursive: true });
+  await mkdir(join(DOCS, dir), { recursive: true });
 
+  let written: string; // the page as it stands after this run, for its topics
   if (existing) {
     const page = await Bun.file(join(DOCS, existing)).text();
     const at = page.indexOf("## Solution");
@@ -386,10 +711,13 @@ for (const sol of ordered) {
       report.push([workRef, existing, "ERROR: no '## Solution' heading"]);
       continue;
     }
-    const next = ensureLabel(page.slice(0, at) + solutionSection(sol), sol.header);
+    const tail = page.slice(solutionEnd(page, at));
+    const body = page.slice(0, at) + solutionSection(sol) + (tail ? `\n${tail}` : "");
+    const next = await ensureTopics(ensureIcon(ensureLabel(body, sol.header)), sol);
     const actions: string[] = [];
     if (existing !== name) {
       await rename(join(DOCS, existing), join(DOCS, name));
+      vacated.add(dirname(existing));
       actions.push("moved");
     }
     if (next !== page) {
@@ -397,10 +725,119 @@ for (const sol of ordered) {
       actions.push("updated");
     }
     report.push([workRef, name, actions.join(" + ") || "skipped (in sync)"]);
+    written = next;
   } else {
-    const topic = topics.get(sol.num) ?? sol.category;
-    await Bun.write(join(DOCS, name), renderPage(sol, topic));
+    const page = renderPage(sol, await fetchTopicTags(sol));
+    await Bun.write(join(DOCS, name), page);
     report.push([workRef, name, "created"]);
+    written = page;
+  }
+  for (const tag of frontmatterTopics(written)) {
+    tags.set(tag.slug, tag);
+    tagged.set(tag.slug, (tagged.get(tag.slug) ?? 0) + 1);
+  }
+  // The route drops the phase `(group)` and the page's number prefix.
+  redirects.push(`  { from: "/${sol.num}", to: ${JSON.stringify(`/${slugify(topic.name)}/${sol.slug}`)} },`);
+}
+
+// Script-owned short links, one per page; imported by blume.config.ts.
+{
+  const module = [
+    "// Generated by `bun run sync` (apps/cli/sync.ts) — do not edit.",
+    "// `/leetcode/<num>` → that problem's page; exact paths, base added by Blume.",
+    "export default [",
+    ...redirects,
+    "];",
+    "",
+  ].join("\n");
+  if (!(await Bun.file(REDIRECTS).exists()) || (await Bun.file(REDIRECTS).text()) !== module) {
+    await Bun.write(REDIRECTS, module);
+    report.push([`${redirects.length} redirects`, "apps/docs/redirects.ts", "written"]);
+  }
+}
+
+// One guide page per tag that no campaign topic teaches, created when missing
+// (an empty file counts as missing) and never rewritten. A guide is found by
+// slug anywhere under guides/ — a human files it into a category `(group)`,
+// which leaves its route alone — and a new one lands at the guides/ root. A
+// guide whose tag no page carries any more is left alone: it is hand-owned.
+const guideTags = [...tags.values()]
+  .filter((tag) => !TOPIC_LANDINGS[tag.slug])
+  .sort((a, b) => a.slug.localeCompare(b.slug));
+const guideFiles = new Map<string, string>(); // slug -> path relative to DOCS
+for await (const rel of new Bun.Glob("guides/**/*.mdx").scan(DOCS)) guideFiles.set(basename(rel, ".mdx"), rel);
+for (const tag of guideTags) {
+  const rel = guideFiles.get(tag.slug) ?? `guides/${tag.slug}.mdx`;
+  const file = Bun.file(join(DOCS, rel));
+  if ((await file.exists()) && file.size > 0) continue;
+  await Bun.write(file, guidePage(tag));
+  report.push([`tag ${tag.slug}`, rel, "created"]);
+}
+
+// Every guide's sidebar badge is its backlink count: the problem pages whose
+// tag badge links to it, which is every page carrying the tag, since a guide's
+// tag has no landing (`tagTarget()`). A guide whose tag a landing has since
+// claimed has no backlinks left. Counts move with every solved problem, so the
+// badge is rewritten whenever it differs; the rest of the guide is untouched.
+// The same pass checks each guide's hand-picked `icon:`, which is also the icon
+// on every problem-page badge linking to the guide: it must exist, must not be
+// a topic group's (`TOPIC_ICONS`), so a guide badge never reads as a topic's,
+// and must not be another guide's.
+const topicIcons = new Set(Object.values(TOPIC_ICONS));
+const guideIcons = new Map<string, string>(); // icon -> the guide that took it first
+for await (const rel of new Bun.Glob("guides/**/*.mdx").scan(DOCS)) {
+  const slug = basename(rel, ".mdx");
+  const count = TOPIC_LANDINGS[slug] ? 0 : (tagged.get(slug) ?? 0);
+  const page = await Bun.file(join(DOCS, rel)).text();
+  const icon = page.match(/^---\n[\s\S]*?\n---/)?.[0].match(/^icon: (\S+)$/m)?.[1];
+  if (!icon) console.warn(`${rel}: no icon; its badges render without one — file it and add \`icon:\``);
+  else if (topicIcons.has(icon)) console.warn(`${rel}: icon ${JSON.stringify(icon)} is a topic's (TOPIC_ICONS); pick another`);
+  else if (guideIcons.has(icon)) console.warn(`${rel}: icon ${JSON.stringify(icon)} is ${guideIcons.get(icon)}'s too; pick another`);
+  else guideIcons.set(icon, rel);
+  const next = withBacklinkBadge(page, count);
+  if (next === page) continue;
+  await Bun.write(join(DOCS, rel), next);
+  report.push([`${count} backlinks`, rel, "badged"]);
+}
+
+// Phase metas: created when missing (an empty file counts as missing), never
+// rewritten, so a renamed phase title survives every sync.
+for (const [dir, phase] of phases) {
+  const file = Bun.file(join(DOCS, dir, "meta.ts"));
+  if ((await file.exists()) && file.size > 0) continue;
+  await Bun.write(file, phaseMeta(phase));
+  report.push([`phase ${phase.order}`, `${dir}/meta.ts`, "created"]);
+}
+
+// Script-owned folder metas — one per live topic folder, plus guides/ —
+// rewritten only when they differ.
+const metas: [label: string, dir: string, meta: string][] = [
+  ...[...groups].map(([dir, topic]): [string, string, string] => [`topic ${topic.order ?? "-"}`, dir, groupMeta(topic)]),
+  ...(guideTags.length ? [["guides", "guides", GUIDES_META] as [string, string, string]] : []),
+];
+for (const [label, dir, meta] of metas) {
+  const path = join(DOCS, dir, "meta.ts");
+  if ((await Bun.file(path).exists()) && (await Bun.file(path).text()) === meta) continue;
+  await Bun.write(path, meta);
+  report.push([label, `${dir}/meta.ts`, "written"]);
+}
+
+// A folder every page left behind is dead: drop its meta and the folder itself,
+// then the phase folder above it if that emptied too. A folder that still holds
+// anything else (a hand-written index.mdx, another topic) stops the climb.
+for (const start of vacated) {
+  for (let dir = start; dir !== "."; dir = dirname(dir)) {
+    if (groups.has(dir) || phases.has(dir)) break;
+    let left: string[];
+    try {
+      left = await readdir(join(DOCS, dir));
+    } catch {
+      break; // already removed via a sibling's climb
+    }
+    if (left.some((f) => f !== "meta.ts")) break;
+    if (left.length) await unlink(join(DOCS, dir, "meta.ts"));
+    await rmdir(join(DOCS, dir));
+    report.push(["", dir, "removed (empty)"]);
   }
 }
 

apps/cli/topics.ts

@@ -0,0 +1,75 @@
+/**
+ * Topic issues and their problem sub-issues: the ONE reading of "is this topic
+ * finished", shared by close-topics.ts (closes the topic issue) and
+ * release-topics.ts (publishes the topic's timever release) so the two can
+ * never disagree about when a topic was done.
+ *
+ * Rule: a topic is finished when it has a core set (`set:core` sub-issues) and
+ * every one of them is closed. Optional and deferred problems are extra credit
+ * and never hold a topic open. A topic with no core sub-issues is never
+ * finished — that would be indistinguishable from a mis-labelled problem set.
+ *
+ * Library: side-effect-free on import; every call takes the caller's github().
+ */
+import type { GitHub } from "./github.ts";
+
+/** One problem sub-issue, narrowed from the sub_issues payload. */
+export interface Problem {
+  number: number;
+  /** `LC <num> · <Name>`. */
+  title: string;
+  /** ISO instant the issue closed; null while it is open. */
+  closedAt: string | null;
+  labels: string[];
+}
+
+export interface Core {
+  /** Core sub-issues, closed and open alike, lowest number first. */
+  all: number[];
+  /** The core sub-issues still open — non-empty means the topic stays open. */
+  pending: number[];
+  /** When the last core sub-issue closed; null until the topic is finished. */
+  finishedAt: string | null;
+}
+
+/**
+ * Every sub-issue of a topic. The sub_issues payload carries the full issue
+ * objects (state + labels), so no per-problem follow-up request is needed.
+ */
+export async function readProblems(gh: GitHub, topic: number): Promise<Problem[]> {
+  const problems: Problem[] = [];
+  for await (const raw of gh.list(`/repos/${gh.repo}/issues/${topic}/sub_issues`)) {
+    if (!raw || typeof raw !== "object") continue;
+    if (!("number" in raw) || typeof raw.number !== "number") continue;
+    if (!("title" in raw) || typeof raw.title !== "string") continue;
+    if (!("state" in raw) || typeof raw.state !== "string") continue;
+    if (!("labels" in raw) || !Array.isArray(raw.labels)) continue;
+    const closedAt =
+      raw.state === "closed" && "closed_at" in raw && typeof raw.closed_at === "string"
+        ? raw.closed_at
+        : null;
+    const labels = raw.labels.flatMap((label: unknown) =>
+      label && typeof label === "object" && "name" in label && typeof label.name === "string"
+        ? [label.name]
+        : [],
+    );
+    problems.push({ number: raw.number, title: raw.title, closedAt, labels });
+  }
+  return problems.sort((a, b) => a.number - b.number);
+}
+
+/** The value of a `prefix:value` label (`set:` → `core`), if the problem has one. */
+export function labelValue(problem: Problem, prefix: string): string | undefined {
+  return problem.labels.find((l) => l.startsWith(prefix))?.slice(prefix.length);
+}
+
+export function coreSet(problems: Problem[]): Core {
+  const core = problems.filter((p) => labelValue(p, "set:") === "core");
+  const pending = core.filter((p) => !p.closedAt).map((p) => p.number);
+  // ISO instants from the API share one format, so string order is time order.
+  const finishedAt =
+    core.length && !pending.length
+      ? core.map((p) => p.closedAt!).reduce((a, b) => (a > b ? a : b))
+      : null;
+  return { all: core.map((p) => p.number), pending, finishedAt };
+}

apps/cli/tui.ts

@@ -0,0 +1,214 @@
+/**
+ * Terminal drawing primitives for the stats dashboard: colour, block-glyph
+ * charts, and the alternate-screen plumbing.
+ *
+ * Hand-rolled for the same reason apps/api/src/charts.ts and png.ts are — the
+ * repo carries near-zero runtime dependencies, and everything a progress
+ * dashboard needs is a bar, a sparkline and a coloured cell. The palette is
+ * charts.ts's, so the terminal, the README SVGs and the digest email are the
+ * same picture in three renderers.
+ *
+ * Side-effect-free on import except for reading the colour environment once;
+ * nothing is written to the terminal until openScreen() is called.
+ */
+
+// ── palette (apps/api/src/charts.ts) ─────────────────────────────
+
+export const FG = "#fafafa"; // zinc-50 text
+export const MUTED = "#a1a1aa"; // zinc-400 secondary text
+export const LINE = "#27272a"; // zinc-800 structure / empty track
+export const GREEN = "#16a34a"; // green-600 (core / pass)
+export const BLUE = "#2563eb"; // blue-600 (optional)
+export const YELLOW = "#eab308"; // yellow-500 (attention)
+export const RED = "#f87171"; // red-400 (fail, on dark)
+
+/** GitHub dark-mode contribution hues; level 0 is the empty cell. */
+export const GREENS = ["#27272a", "#0e4429", "#006d32", "#26a641", "#39d353"];
+
+// ── colour ───────────────────────────────────────────────────────
+
+/**
+ * Honour NO_COLOR and pipes, and let FORCE_COLOR override both — the dashboard
+ * is legible without colour, and `bun run stats | less -R` should still be.
+ */
+export const COLOR =
+  process.env.FORCE_COLOR !== undefined
+    ? process.env.FORCE_COLOR !== "0"
+    : process.env.NO_COLOR === undefined && process.stdout.isTTY === true;
+
+const RESET = "\x1b[0m";
+
+function channels(hex: string): string {
+  return `${parseInt(hex.slice(1, 3), 16)};${parseInt(hex.slice(3, 5), 16)};${parseInt(hex.slice(5, 7), 16)}`;
+}
+
+export function fg(hex: string, text: string): string {
+  return COLOR ? `\x1b[38;2;${channels(hex)}m${text}${RESET}` : text;
+}
+
+export function bg(hex: string, text: string): string {
+  return COLOR ? `\x1b[48;2;${channels(hex)}m${text}${RESET}` : text;
+}
+
+export function bold(text: string): string {
+  return COLOR ? `\x1b[1m${text}${RESET}` : text;
+}
+
+const ANSI = /\x1b\[[0-9;]*m/g;
+
+/** Printable width — every glyph used here is one cell wide. */
+export function width(text: string): number {
+  return text.replace(ANSI, "").length;
+}
+
+/** Pad or cut a *plain* string to exactly n cells; colour it afterwards. */
+export function cell(text: string, n: number, align: "left" | "right" = "left"): string {
+  const clipped = text.length > n ? `${text.slice(0, Math.max(0, n - 1))}…` : text;
+  return align === "left" ? clipped.padEnd(n) : clipped.padStart(n);
+}
+
+/** Pad an already-coloured string to n cells. */
+export function padTo(text: string, n: number): string {
+  return text + " ".repeat(Math.max(0, n - width(text)));
+}
+
+// ── charts ───────────────────────────────────────────────────────
+
+const EIGHTHS = ["", "▏", "▎", "▍", "▌", "▋", "▊", "▉"];
+const SPARKS = ["▁", "▂", "▃", "▄", "▅", "▆", "▇", "█"];
+
+/**
+ * Filled and empty. The two differ by GLYPH as well as by colour, so a bar
+ * still reads under NO_COLOR or in a pipe — every chart here has to survive
+ * `bun run stats > notes.txt`.
+ */
+const FILL = "█";
+const TRACK = "░";
+
+/**
+ * One bar over a muted track, `cells` wide. Sub-cell remainders use the
+ * eighth-block glyphs, so one solved problem out of 161 still shows.
+ */
+export function bar(value: number, total: number, cells: number, color = GREEN): string {
+  const units = Math.round(Math.max(0, Math.min(1, total > 0 ? value / total : 0)) * cells * 8);
+  const filled = FILL.repeat(Math.floor(units / 8)) + EIGHTHS[units % 8]!;
+  return fg(color, filled) + fg(LINE, TRACK.repeat(Math.max(0, cells - filled.length)));
+}
+
+export interface Segment {
+  value: number;
+  color: string;
+  /** Defaults to the solid block; pass TRACK-ish glyphs for "not done yet". */
+  glyph?: string;
+}
+
+/**
+ * Segments laid end to end, `total` mapped to `cells`. Anything short of
+ * `total` is left BLANK, not tracked: bars sharing a scale must show their
+ * different lengths. A caller wanting a visible remainder passes it as a
+ * segment of its own.
+ *
+ * Non-zero segments are floored but never vanish; the overshoot that floor
+ * creates is taken back from the widest segment, which can spare it.
+ */
+export function stackedBar(segments: Segment[], total: number, cells: number): string {
+  if (total <= 0) return " ".repeat(cells);
+  const widths = segments.map((s) =>
+    s.value > 0 ? Math.max(1, Math.floor((s.value / total) * cells)) : 0,
+  );
+  let over = widths.reduce((a, b) => a + b, 0) - cells;
+  while (over > 0) {
+    const i = widths.indexOf(Math.max(...widths));
+    if (widths[i]! <= 1) break;
+    widths[i]!--;
+    over--;
+  }
+  const drawn = widths.map((n, i) => fg(segments[i]!.color, (segments[i]!.glyph ?? FILL).repeat(n)));
+  return drawn.join("") + " ".repeat(Math.max(0, cells - widths.reduce((a, b) => a + b, 0)));
+}
+
+/**
+ * One cell of the campaign heatmap. With colour it is the GREENS ramp the
+ * README and the digest use; without it, the same five levels as shading.
+ */
+export function heatCell(attempts: number, body: string): string {
+  const level = Math.min(attempts, GREENS.length - 1);
+  return COLOR ? bg(GREENS[level]!, body) : [" ", "·", "▒", "▓", "█"][level]!.repeat(body.length);
+}
+
+/** One glyph per value, scaled to the largest. All-zero renders as a floor. */
+export function sparkline(values: number[], color = GREEN): string {
+  const peak = Math.max(...values, 0);
+  const line = values
+    .map((v) => (peak === 0 ? SPARKS[0]! : SPARKS[Math.min(7, Math.round((v / peak) * 7))]!))
+    .join("");
+  return fg(color, line);
+}
+
+// ── layout ───────────────────────────────────────────────────────
+
+/** A section rule that fills the width: `── name ────────────`. */
+export function rule(title: string, cells: number): string {
+  const label = ` ${title} `;
+  return (
+    fg(LINE, "──") + fg(MUTED, label) + fg(LINE, "─".repeat(Math.max(0, cells - 2 - label.length)))
+  );
+}
+
+// ── screen ───────────────────────────────────────────────────────
+
+const ALT_ON = "\x1b[?1049h\x1b[?25l";
+const ALT_OFF = "\x1b[?25h\x1b[?1049l";
+
+export interface Screen {
+  readonly rows: number;
+  readonly columns: number;
+  /** Draw a frame, clipped to the terminal height. */
+  draw(lines: string[]): void;
+  close(): void;
+}
+
+/**
+ * Take over the terminal: alternate buffer, hidden cursor, raw keys. `onKey`
+ * receives the raw chunk (`"\t"`, `"\x1b[B"`, `"q"`, …) — decoding belongs to
+ * the app, which is the only thing that knows what a key means.
+ *
+ * The caller MUST close() in a finally: raw mode survives a thrown exception.
+ */
+export function openScreen(onKey: (chunk: string) => void, onResize: () => void): Screen {
+  const out = process.stdout;
+  const input = process.stdin;
+
+  out.write(ALT_ON);
+  input.setRawMode?.(true);
+  input.setEncoding("utf8");
+  input.resume();
+  input.on("data", onKey);
+  out.on("resize", onResize);
+
+  let closed = false;
+  return {
+    get rows() {
+      return out.rows ?? 24;
+    },
+    get columns() {
+      return out.columns ?? 80;
+    },
+    draw(lines: string[]): void {
+      const visible = lines.slice(0, this.rows);
+      // Home, then erase each line as it is rewritten plus everything below the
+      // last one. No full clear, so a redraw does not flash, and no trailing
+      // newline, which would scroll the alternate screen by a row per frame.
+      out.write(`\x1b[H${visible.map((l) => `${l}\x1b[K`).join("\r\n")}\x1b[J`);
+    },
+    close(): void {
+      if (closed) return;
+      closed = true;
+      input.off("data", onKey);
+      out.off("resize", onResize);
+      input.setRawMode?.(false);
+      input.pause();
+      out.write(ALT_OFF);
+    },
+  };
+}

apps/cli/videos.ts

@@ -0,0 +1,171 @@
+#!/usr/bin/env bun
+/**
+ * Find the NeetCode explanation video for every docs page that has none.
+ *
+ * A finished solution page carries frontmatter `video: <YouTube id>` —
+ * NeetCode's walkthrough of the problem — which the docs MDX `wrapper`
+ * (`apps/docs/components/ProblemBadges.astro`) renders as the red
+ * "Explanation" badge beside the topic badges. `sync.ts` never writes that key
+ * (it owns `icon:`, `topics:` and `## Solution`), so pages accumulate without
+ * one. This script lists every numbered page lacking `video:` and looks each
+ * up on NeetCode's two channels, main channel first, accepting only a title
+ * that names the page's exact LC number (`… - Leetcode 226 - …`) and is not a
+ * #short. No YouTube API key: the channel search page embeds its results as
+ * `ytInitialData` JSON, which is all we parse. Ranking is the channel's own —
+ * the first exact-number match wins.
+ *
+ *   bun apps/cli/videos.ts           # report: page → video (or "no match")
+ *   bun apps/cli/videos.ts --write   # also add `video:` to the frontmatter
+ *
+ * --write inserts the key before `sidebar:`. A page with no match is left
+ * untouched, so re-runs are no-ops once every page has its video.
+ */
+import { join } from "node:path";
+
+import { printTable } from "./report.ts";
+import { ROOT } from "./work.ts";
+
+const DOCS = join(ROOT, "apps", "docs", "content");
+const WRITE = process.argv.includes("--write");
+
+/** Channel handles searched in order; the first exact match wins. */
+const CHANNELS = ["NeetCode", "NeetCodeIO"] as const;
+
+interface Video {
+  id: string;
+  title: string;
+  channel: string;
+}
+
+// ── YouTube channel search (no API key) ──────────────────────────
+
+const HEADERS = { "accept-language": "en-US,en;q=0.9", "user-agent": "Mozilla/5.0" };
+
+/**
+ * The `var ytInitialData = {…};</script>` blob of a YouTube page, parsed.
+ * YouTube intermittently answers 200 with a page that lacks the blob or cuts
+ * it short, so a bad page is retried a few times before it is an error.
+ */
+async function initialData(url: string): Promise<unknown> {
+  let reason = "";
+  for (let attempt = 0; attempt < 3; attempt++) {
+    if (attempt) await Bun.sleep(500 * attempt);
+    const res = await fetch(url, { headers: HEADERS });
+    if (!res.ok) {
+      reason = `status ${res.status}`;
+      continue;
+    }
+    const html = await res.text();
+    // Slice rather than regex: the blob is ~1 MB, and a lazy `.*?` across it
+    // is what made the first cut of this script fail at random.
+    const open = html.search(/ytInitialData\s*=\s*\{/);
+    const close = open === -1 ? -1 : html.indexOf("</script>", open);
+    if (close === -1) {
+      reason = `no ytInitialData in ${html.length}-byte page`;
+      continue;
+    }
+    try {
+      return JSON.parse(html.slice(html.indexOf("{", open), close).replace(/;\s*$/, ""));
+    } catch {
+      reason = "truncated ytInitialData";
+    }
+  }
+  throw new Error(`GET ${url} -> ${reason}`);
+}
+
+/** Every videoRenderer in a channel search page, in the page's own order. */
+async function channelSearch(channel: string, query: string): Promise<Video[]> {
+  const url = `https://www.youtube.com/@${channel}/search?query=${encodeURIComponent(query)}`;
+  const data = await initialData(url);
+
+  const videos: Video[] = [];
+  const walk = (node: unknown): void => {
+    if (!node || typeof node !== "object") return;
+    if ("videoRenderer" in node) {
+      const v = node.videoRenderer;
+      if (v && typeof v === "object" && "videoId" in v && typeof v.videoId === "string") {
+        const runs =
+          "title" in v && v.title && typeof v.title === "object" && "runs" in v.title
+            ? v.title.runs
+            : undefined;
+        const title = Array.isArray(runs)
+          ? runs.map((r) => (r && typeof r === "object" && "text" in r ? String(r.text) : "")).join("")
+          : "";
+        videos.push({ id: v.videoId, title, channel });
+      }
+      return;
+    }
+    for (const child of Object.values(node)) walk(child);
+  };
+  walk(data);
+  return videos;
+}
+
+/** The LC number a NeetCode title names (`… - Leetcode 226 - …`), if any. */
+function titledNumber(title: string): number | undefined {
+  const m = title.match(/\bleetcode\s*#?\s*(\d+)\b/i);
+  return m ? Number(m[1]) : undefined;
+}
+
+async function findVideo(num: number): Promise<Video | undefined> {
+  for (const channel of CHANNELS) {
+    const hit = (await channelSearch(channel, `leetcode ${num}`)).find(
+      (v) => titledNumber(v.title) === num && !/#shorts\b/i.test(v.title),
+    );
+    if (hit) return hit;
+  }
+  return undefined;
+}
+
+// ── docs pages ───────────────────────────────────────────────────
+
+interface Page {
+  num: number;
+  rel: string;
+  text: string;
+}
+
+/** The page's frontmatter block, `---` to `---`. */
+const FRONTMATTER = /^---\n[\s\S]*?\n---/;
+
+/** Numbered solution pages without a `video:` key, by LC number. */
+async function pagesMissingVideo(): Promise<Page[]> {
+  const pages: Page[] = [];
+  for (const rel of await Array.fromAsync(new Bun.Glob("**/*.mdx").scan(DOCS))) {
+    const text = await Bun.file(join(DOCS, rel)).text();
+    const t = text.match(/^title: '(\d+)\./m);
+    const fm = text.match(FRONTMATTER)?.[0] ?? "";
+    if (t && !/^video:/m.test(fm)) pages.push({ num: Number(t[1]), rel, text });
+  }
+  return pages.sort((a, b) => a.num - b.num);
+}
+
+// ── main ─────────────────────────────────────────────────────────
+
+const missing = await pagesMissingVideo();
+if (missing.length === 0) {
+  console.log("every solution page has a video");
+  process.exit(0);
+}
+
+const rows: string[][] = [["docs page", "video", "title", WRITE ? "status" : ""]];
+let found = 0;
+for (const page of missing) {
+  const video = await findVideo(page.num);
+  if (!video) {
+    rows.push([page.rel, "—", "no NeetCode match", WRITE ? "skipped" : ""]);
+    continue;
+  }
+  found++;
+  let status = "";
+  if (WRITE) {
+    const next = page.text.replace(FRONTMATTER, (fm) => fm.replace(/^sidebar:$/m, `video: ${JSON.stringify(video.id)}\nsidebar:`));
+    await Bun.write(join(DOCS, page.rel), next);
+    status = "written";
+  }
+  rows.push([page.rel, `https://youtu.be/${video.id}`, `${video.title} (${video.channel})`, status]);
+}
+
+if (!WRITE) for (const row of rows) row.pop();
+printTable(rows);
+console.log(`\n${found}/${missing.length} page(s) matched${WRITE ? `, ${found} written` : ""}`);

apps/cli/work.ts

@@ -93,6 +93,25 @@ export function scanBucket(bucket: Bucket): Map<number, WorkFile[]> {
   return files;
 }
 
+/**
+ * Is this file a real solution rather than an empty scaffold? The same call
+ * close-solved.ts makes before it closes an issue — a stub under work/1 is a
+ * problem still unsolved, and owes no review.
+ */
+export function isSolution(file: WorkFile): boolean {
+  const source = readFileSync(join(WORK, file.rel), "utf8");
+  return isImplemented(source, file.rel.endsWith(".py") ? "py" : "js");
+}
+
+/** Problems in a bucket with a solution on disk; scaffolds do not count. */
+export function solvedInBucket(bucket: Bucket): number {
+  let solved = 0;
+  for (const files of scanBucket(bucket).values()) {
+    if (files.some(isSolution)) solved++;
+  }
+  return solved;
+}
+
 /**
  * LC number -> ET date of the commit that first added a work/ file for it.
  *
@@ -153,14 +172,12 @@ export function reviewQueues(today: string): Map<Window, Owed[]> {
   const dates = firstSolved();
 
   // An empty scaffold under work/1 is a problem still unsolved, not one owing
-  // a review — the same call close-solved.ts makes before it closes an issue.
+  // a review.
   const solved: { file: WorkFile; date: string }[] = [];
   for (const files of scanBucket(1).values()) {
     const date = dates.get(files[0]!.lc);
     if (date === undefined) continue; // uncommitted: you only just solved it
-    const file = files.find((f) =>
-      isImplemented(readFileSync(join(WORK, f.rel), "utf8"), f.rel.endsWith(".py") ? "py" : "js"),
-    );
+    const file = files.find(isSolution);
     if (file) solved.push({ file, date });
   }
 

apps/docs/blume.config.ts

@@ -1,21 +1,185 @@
 import { defineConfig } from "blume";
+import type { StandardSchema } from "blume/core/standard-schema.ts";
+import { custom, filesystem } from "blume/sources";
+import { githubReleasesSource } from "blume/sources/github-releases.ts";
+import redirects from "./redirects";
+
+/**
+ * GitHub releases → /changelog, dated by the topic's real finish instant.
+ *
+ * Blume dates a release entry by `published_at`, which the GitHub API cannot
+ * backdate — so the topic releases backfilled on one day (apps/cli/
+ * release-topics.ts) would all read that day. Their tags are timever
+ * (`YYYYMMDD.HHMMSS.NNNNNNNNN`, UTC) of the moment the topic finished, so this
+ * fetch rewrites each timever release's `published_at` to that instant before
+ * Blume maps it; anything else passes through untouched. The config-level
+ * `githubReleases()` accepts no `fetchImpl`, hence the `custom()` wrap of the
+ * underlying source (the `blume/sources/*.ts` path the Blume docs use for
+ * custom sources), with the context the built-in adapter would receive.
+ */
+const TIMEVER = /^(\d{4})(\d{2})(\d{2})\.(\d{2})(\d{2})(\d{2})\.\d{9}$/;
+
+const releasesDatedByTag: typeof fetch = async (input, init) => {
+  const res = await fetch(input, init);
+  if (!res.ok) return res;
+  const releases: unknown = await res.json();
+  if (Array.isArray(releases)) {
+    for (const release of releases) {
+      const m =
+        typeof release?.tag_name === "string"
+          ? release.tag_name.match(TIMEVER)
+          : null;
+      if (m)
+        release.published_at = `${m[1]}-${m[2]}-${m[3]}T${m[4]}:${m[5]}:${m[6]}Z`;
+    }
+  }
+  // Blume reads only `ok` and the JSON body, so the original headers (whose
+  // content-length/encoding describe the upstream bytes) are not carried over.
+  return Response.json(releases, { status: res.status });
+};
+
+// Blume's defaults (`inter`, `ibm-plex-mono`) are fetched from fonts.gstatic.com
+// on every build, which has timed out on the Pages runner and, fully offline,
+// silently ships no fonts at all. The same two families from Fontsource, as
+// local files, keep the build network-free. Blume resolves `src` from this
+// directory; the workspace links these packages under ./node_modules.
+const inter = {
+  name: "Inter",
+  variants: [
+    {
+      src: "./node_modules/@fontsource-variable/inter/files/inter-latin-wght-normal.woff2",
+      weight: "100..900",
+    },
+  ],
+};
+const plexMono = {
+  name: "IBM Plex Mono",
+  variants: [
+    {
+      src: "./node_modules/@fontsource/ibm-plex-mono/files/ibm-plex-mono-latin-400-normal.woff2",
+      weight: 400,
+    },
+    {
+      src: "./node_modules/@fontsource/ibm-plex-mono/files/ibm-plex-mono-latin-500-normal.woff2",
+      weight: 500,
+    },
+  ],
+};
+
+/**
+ * Custom frontmatter, rendered as the badge row by
+ * components/ProblemBadges.astro. Problem pages: `topics:` is LeetCode's topic
+ * tags (written by apps/cli/sync.ts), `video:` the NeetCode walkthrough's
+ * YouTube id (apps/cli/videos.ts). Guide pages (content/guides/, created by
+ * sync): `list:` is the tag's LeetCode problem list. Blume rejects undeclared
+ * keys and takes any Standard Schema; these are hand-rolled so the docs
+ * workspace needs no zod. All optional — every other page carries none.
+ */
+const optional = <T>(
+  message: string,
+  valid: (value: unknown) => value is T,
+): StandardSchema<unknown, T | undefined> => ({
+  "~standard": {
+    version: 1,
+    vendor: "prdlk",
+    validate: (value) =>
+      value === undefined || valid(value)
+        ? { value }
+        : { issues: [{ message }] },
+  },
+});
+
+const topicsSchema = optional(
+  "expected a list of { name, slug } LeetCode topic tags",
+  (value): value is { name: string; slug: string }[] =>
+    Array.isArray(value) &&
+    value.every(
+      (t) => typeof t?.name === "string" && typeof t?.slug === "string",
+    ),
+);
+const videoSchema = optional(
+  "expected an 11-character YouTube video id",
+  (value): value is string =>
+    typeof value === "string" && /^[\w-]{11}$/.test(value),
+);
+const listSchema = optional(
+  "expected a https://leetcode.com/problem-list/<slug>/ URL",
+  (value): value is string =>
+    typeof value === "string" &&
+    /^https:\/\/leetcode\.com\/problem-list\/[\w-]+\/$/.test(value),
+);
 
 export default defineConfig({
-  title: "Leetcode",
-  description: "Documentation for LeetCode solutions",
+  title: "prdlk",
+  description: "Documentation for my LeetCode solutions",
+  logo: "./public/logo.svg",
   deployment: {
-    site: "https://prdlk.github.io",
-    base: "/leetcode",
+    site: "https://lc.prd.lk",
+  },
+  github: {
+    owner: "prdlk",
+    repo: "leetcode",
+  },
+  lastModified: "git",
+  redirects,
+  frontmatter: {
+    extend: { topics: topicsSchema, video: videoSchema, list: listSchema },
+  },
+  seo: {
+    og: { enabled: true },
+    rss: { enabled: true, types: ["changelog"] },
+    sitemap: true,
+    robots: true,
+    structuredData: true,
+    x: { handle: "@prdlk" },
+  },
+  // Blume's own assistant route is server-rendered (it reads the provider key
+  // per request), which a static Pages build cannot ship. The SRS Worker
+  // answers instead (apps/api/src/ask.ts: OpenRouter, grounded on this site's
+  // llms-full.txt, which `agents.llmsTxt` publishes).
+  ai: {
+    assistant: {
+      enabled: true,
+      endpoint: "https://srs-api.prdlk.workers.dev/ask",
+    },
+  },
+  agents: {
+    llmsTxt: true,
+    mcp: { enabled: false },
   },
   content: {
-    root: "content",
+    sources: [
+      filesystem({ root: "content" }),
+      custom(
+        githubReleasesSource(
+          {
+            name: "changelog",
+            prefix: "changelog",
+            owner: "prdlk",
+            repo: "leetcode",
+            fetchImpl: releasesDatedByTag,
+          },
+          // What resolve.ts hands the built-in adapter: `.blume/cache/<name>/`,
+          // and a refresh on every load (the source reads nothing else).
+          {
+            projectRoot: import.meta.dirname,
+            cacheDir: `${import.meta.dirname}/.blume/cache/changelog`,
+            mode: "build",
+          },
+        ),
+      ),
+    ],
+  },
+  theme: {
+    fonts: { display: inter, body: inter, mono: plexMono },
   },
   navigation: {
-    tabs: [
-      {
-        label: "Reference",
-        path: "/reference",
+    sidebar: {
+      display: "flat", // "flat" | "group" | "page"
     },
+    tabs: [
+      { label: "Guides", path: "/guides" },
+      { label: "Changelog", path: "/changelog" },
     ],
   },
 });

apps/docs/components.json

@@ -0,0 +1,21 @@
+{
+  "$schema": "https://ui.shadcn.com/schema.json",
+  "style": "new-york",
+  "rsc": false,
+  "tsx": true,
+  "tailwind": {
+    "config": "",
+    "css": "theme.css",
+    "baseColor": "neutral",
+    "cssVariables": true,
+    "prefix": ""
+  },
+  "iconLibrary": "lucide",
+  "aliases": {
+    "components": "@/components",
+    "utils": "@/lib/utils",
+    "ui": "@/components/ui",
+    "lib": "@/lib",
+    "hooks": "@/hooks"
+  }
+}

apps/docs/components.ts

@@ -0,0 +1,20 @@
+/**
+ * Project MDX components, available on every page with no import, and layout
+ * slot overrides. Static `.astro` files ship no framework JS (a custom element
+ * carries any behaviour); interactive React lives in `islands/` instead.
+ */
+import { defineComponents } from "blume";
+
+export default defineComponents({
+  mdx: {
+    Carousel: "./components/Carousel.astro",
+    CarouselImage: "./components/CarouselImage.astro",
+    // MDX's own content wrapper: problem pages' topic + explanation badges, from
+    // `topics:` / `video:` frontmatter, between the description and the body.
+    wrapper: "./components/ProblemBadges.astro",
+  },
+  layout: {
+    // Topic landing + guide pages' "what links here": every problem pointing at the page.
+    PageFooter: "./components/BacklinksList.astro",
+  },
+});

apps/docs/components/BacklinksList.astro

@@ -0,0 +1,94 @@
+---
+/**
+ * The `PageFooter` slot: an Obsidian-style backlinks list under a topic landing
+ * or guide page — every problem page that points at it, as `<num> <name>`
+ * rows in LeetCode-number order. Pages nothing points at (problem pages, the
+ * overview, the changelog) render nothing.
+ *
+ * A problem points at a page when either
+ * - one of its topic badges links there — the same `tagTarget()` answer
+ *   `ProblemBadges.astro` renders, so this list and the badges cannot drift
+ *   (a DFS problem is a backlink of the one DFS landing its badge picks); or
+ * - it lives under the page's route (`/hybrid-structures/lru-cache` under
+ *   `/hybrid-structures`), so a topic no LeetCode tag names still lists its
+ *   own problems.
+ *
+ * Problem pages are recognised by their `<num>. <name>` title, the shape
+ * `apps/cli/sync.ts` writes.
+ *
+ * The list is a native `<details>`, open on load: the chevron at the top
+ * right of the header row collapses it like an accordion, with no JS.
+ */
+import { getEntry } from "astro:content";
+import data from "blume:data";
+import { withBase } from "blume/components/islands/base-path.ts";
+import Icon from "blume/components/Icon.astro";
+import { tagTarget, type TopicTag } from "../topic-landings.ts";
+
+interface Props {
+  route: string;
+}
+
+interface Route {
+  path: string;
+  title: string;
+  collection: string;
+  entryId: string;
+}
+
+const { route } = Astro.props;
+const routes: Route[] = data.routes;
+const served = new Set(routes.map((r) => r.path));
+
+const problems = routes.flatMap((r) => {
+  const m = r.title.match(/^(\d+)\.\s+(.+)$/);
+  return m ? [{ route: r, num: Number(m[1]), name: m[2]! }] : [];
+});
+
+// A problem page is never a backlink target: skip the per-problem lookups there.
+const backlinks = problems.some((p) => p.route.path === route)
+  ? []
+  : (
+      await Promise.all(
+        problems.map(async (p) => {
+          if (p.route.path.startsWith(`${route}/`)) return p;
+          const entry = await getEntry(p.route.collection, p.route.entryId);
+          const tags: TopicTag[] = entry?.data.topics ?? [];
+          const page = { route: p.route.path, tags };
+          return tags.some((tag) => tagTarget(tag, page, served).href === route) ? p : undefined;
+        }),
+      )
+    )
+      .filter((p) => p !== undefined)
+      .sort((a, b) => a.num - b.num);
+---
+
+{
+  backlinks.length > 0 && (
+    <details
+      class="group not-prose mx-auto mt-12 max-w-content border-border border-t pt-6"
+      open
+    >
+      <summary class="mb-2 flex cursor-pointer list-none items-center justify-between gap-2 text-muted-foreground transition-colors hover:text-foreground [&::-webkit-details-marker]:hidden">
+        <h2 class="flex items-baseline gap-2 font-medium text-xs uppercase tracking-wide" id="backlinks">
+          Backlinks
+          <span class="tabular-nums">{backlinks.length}</span>
+        </h2>
+        <Icon class="shrink-0 transition-transform group-open:rotate-180" name="chevron-down" size={16} />
+      </summary>
+      <ul class="text-sm">
+        {backlinks.map((p) => (
+          <li>
+            <a
+              class="-mx-2 flex items-baseline gap-3 rounded-md px-2 py-1 text-foreground no-underline transition-colors hover:bg-muted"
+              href={withBase(p.route.path)}
+            >
+              <span class="w-10 shrink-0 text-right font-mono text-muted-foreground text-xs tabular-nums">{p.num}</span>
+              <span class="truncate">{p.name}</span>
+            </a>
+          </li>
+        ))}
+      </ul>
+    </details>
+  )
+}

apps/docs/components/Carousel.astro

@@ -0,0 +1,170 @@
+---
+/**
+ * A horizontal carousel of <CarouselImage> slides, built the way Blume's own
+ * content components are: static markup, a custom element for the behaviour,
+ * no framework. The track is a CSS scroll-snap strip (so it also swipes on
+ * touch and the browser does the animation); prev/next sit outside it and
+ * the play toggle sits below with a "n / N" counter.
+ *
+ * `time` is seconds per slide while playing (default 1.25); `autoplay` starts
+ * playing on load. Play wraps around, pauses whenever the tab is hidden, and
+ * never starts on its own for a reader who prefers reduced motion — the
+ * button still works for them. Manual navigation (buttons, arrow keys, swipe)
+ * does not stop playback; it only restarts the interval so a step is never
+ * doubled.
+ */
+import Icon from "blume/components/Icon.astro";
+
+interface Props {
+  /** Seconds each slide stays while playing. */
+  time?: number;
+  autoplay?: boolean;
+}
+
+const { time = 1.25, autoplay = false } = Astro.props;
+
+const buttonClass =
+  "inline-flex size-9 shrink-0 cursor-pointer items-center justify-center rounded-full border border-border bg-background text-muted-foreground transition-colors hover:border-foreground hover:text-foreground disabled:cursor-default disabled:opacity-40";
+---
+
+<blume-carousel
+  class="not-prose my-6 block"
+  data-time={String(time)}
+  data-autoplay={autoplay ? "" : undefined}
+  role="region"
+  aria-roledescription="carousel"
+>
+  <div class="flex items-center gap-3">
+    <button class={buttonClass} data-prev type="button" aria-label="Previous slide">
+      <Icon class="rtl:-scale-x-100" name="chevron-left" size={18} />
+    </button>
+    <div
+      class="flex min-w-0 flex-1 snap-x snap-mandatory overflow-x-auto scroll-smooth rounded-blume [scrollbar-width:none] [&::-webkit-scrollbar]:hidden"
+      data-track
+      tabindex="0"
+      aria-live="polite"
+    >
+      <slot />
+    </div>
+    <button class={buttonClass} data-next type="button" aria-label="Next slide">
+      <Icon class="rtl:-scale-x-100" name="chevron-right" size={18} />
+    </button>
+  </div>
+  <div class="mt-3 flex items-center justify-center gap-3">
+    <button class={buttonClass} data-play type="button" aria-label="Play" aria-pressed="false">
+      <Icon class="[[aria-pressed=true]_&]:hidden" name="play" size={16} />
+      <Icon class="[[aria-pressed=false]_&]:hidden" name="pause" size={16} />
+    </button>
+    <span class="text-muted-foreground text-xs tabular-nums leading-5" data-count></span>
+  </div>
+</blume-carousel>
+
+<script>
+  class BlumeCarousel extends HTMLElement {
+    #track!: HTMLElement;
+    #play!: HTMLButtonElement;
+    #count!: HTMLElement;
+    #timer: number | null = null;
+    #index = 0;
+
+    connectedCallback() {
+      this.#track = this.querySelector("[data-track]")!;
+      this.#play = this.querySelector("[data-play]")!;
+      this.#count = this.querySelector("[data-count]")!;
+      const prev = this.querySelector<HTMLButtonElement>("[data-prev]")!;
+      const next = this.querySelector<HTMLButtonElement>("[data-next]")!;
+
+      const slides = this.#slides().length;
+      if (slides < 2) {
+        for (const b of [prev, next, this.#play]) b.disabled = true;
+      }
+      this.#render();
+
+      prev.addEventListener("click", () => this.#step(-1));
+      next.addEventListener("click", () => this.#step(1));
+      this.#play.addEventListener("click", () => (this.#timer === null ? this.#start() : this.#stop()));
+      this.addEventListener("keydown", (event) => {
+        if (event.key === "ArrowLeft") this.#step(-1);
+        else if (event.key === "ArrowRight") this.#step(1);
+        else return;
+        event.preventDefault();
+      });
+      // Swipes and trackpad scrolls move the track without #step; follow them
+      // once the scroll settles. Settle-only, not per event: a long smooth
+      // scroll from #step passes over intermediate slides and must not be
+      // read back as the reader's position mid-flight.
+      let settle: number | undefined;
+      this.#track.addEventListener(
+        "scroll",
+        () => {
+          window.clearTimeout(settle);
+          settle = window.setTimeout(() => this.#syncFromScroll(), 150);
+        },
+        { passive: true }
+      );
+      document.addEventListener("visibilitychange", this.#onVisibility);
+
+      const reduced = matchMedia("(prefers-reduced-motion: reduce)").matches;
+      if (this.hasAttribute("data-autoplay") && slides > 1 && !reduced) this.#start();
+    }
+
+    disconnectedCallback() {
+      this.#stop();
+      document.removeEventListener("visibilitychange", this.#onVisibility);
+    }
+
+    #slides(): HTMLElement[] {
+      return [...this.#track.querySelectorAll<HTMLElement>(":scope > blume-carousel-image")];
+    }
+
+    #step(delta: number) {
+      const slides = this.#slides();
+      this.#index = (this.#index + delta + slides.length) % slides.length;
+      slides[this.#index]!.scrollIntoView({ block: "nearest", inline: "start", behavior: "smooth" });
+      this.#render();
+      if (this.#timer !== null) this.#start(); // restart the interval from this slide
+    }
+
+    #syncFromScroll() {
+      const at = Math.round(this.#track.scrollLeft / this.#track.clientWidth);
+      if (at !== this.#index && Number.isFinite(at)) {
+        this.#index = Math.min(Math.max(at, 0), this.#slides().length - 1);
+        this.#render();
+      }
+    }
+
+    #start() {
+      this.#stop();
+      const ms = Number(this.dataset.time) * 1000;
+      this.#timer = window.setInterval(() => this.#step(1), ms > 0 ? ms : 1250);
+      this.#play.setAttribute("aria-pressed", "true");
+      this.#play.setAttribute("aria-label", "Pause");
+    }
+
+    #stop() {
+      if (this.#timer !== null) window.clearInterval(this.#timer);
+      this.#timer = null;
+      this.#play.setAttribute("aria-pressed", "false");
+      this.#play.setAttribute("aria-label", "Play");
+    }
+
+    // A background tab keeps its timers but not its layout; resume on return.
+    #wasPlaying = false;
+    #onVisibility = () => {
+      if (document.hidden) {
+        this.#wasPlaying = this.#timer !== null;
+        this.#stop();
+      } else if (this.#wasPlaying) this.#start();
+    };
+
+    #render() {
+      const slides = this.#slides();
+      this.#count.textContent = `${this.#index + 1} / ${slides.length}`;
+      slides.forEach((s, i) => s.setAttribute("aria-hidden", i === this.#index ? "false" : "true"));
+    }
+  }
+
+  if (!customElements.get("blume-carousel")) {
+    customElements.define("blume-carousel", BlumeCarousel);
+  }
+</script>

apps/docs/components/CarouselImage.astro

@@ -0,0 +1,45 @@
+---
+/**
+ * One slide of a <Carousel>: Blume's own <Frame> around an <img>, so a slide
+ * is pixel-identical to a framed image elsewhere on the site — `alt` doubles
+ * as the frame's hint line and `caption` is Markdown, exactly as in Frame.
+ *
+ * `src` accepts what MDX authors already write for images: a URL, a
+ * root-relative `/file.png` (served from public/, prefixed with the deploy
+ * base), or the page-relative `../../public/file.png` form. A relative path
+ * that does not pass through public/ has nothing to serve it, so it is a
+ * build error rather than a silent 404.
+ */
+import Frame from "blume/components/content/Frame.astro";
+import { withBase } from "blume/components/islands/base-path.ts";
+
+interface Props {
+  src: string;
+  alt?: string;
+  caption?: string;
+}
+
+const { src, alt, caption } = Astro.props;
+
+const resolveSrc = (value: string): string => {
+  if (URL.canParse(value)) return value;
+  if (value.startsWith("/")) return withBase(value);
+  const at = value.indexOf("public/");
+  if (at === -1) {
+    throw new Error(
+      `<CarouselImage src="${value}">: a relative src must point into public/ (or use /file.png)`
+    );
+  }
+  return withBase(`/${value.slice(at + "public/".length)}`);
+};
+---
+
+<blume-carousel-image
+  class="block w-full shrink-0 snap-center [&_blume-frame]:my-0"
+  role="group"
+  aria-roledescription="slide"
+>
+  <Frame caption={caption} hint={alt}>
+    <img alt={alt ?? ""} src={resolveSrc(src)} loading="lazy" draggable="false" />
+  </Frame>
+</blume-carousel-image>

apps/docs/components/ProblemBadges.astro

@@ -0,0 +1,135 @@
+---
+/**
+ * The MDX `wrapper`: the badge row between a page's description and its body.
+ * Blume's page template renders the title and description itself and then
+ * the MDX content, with no slot in between, so wrapping the content is the
+ * only way to land right after the description. MDX hands a wrapper no
+ * route, so it is read off the URL, and the page's frontmatter is then
+ * looked up through the route manifest — the same `getEntry` call Blume's own
+ * page template makes. Pages with none of the keys below (landing pages, the
+ * changelog) render only their content.
+ *
+ * - `topics:` (problem pages, written by `apps/cli/sync.ts`) is LeetCode's own
+ *   topic tags. A tag the campaign teaches (`topic-landings.ts`) links to that
+ *   topic's landing page and is filled; any other tag links to its guide
+ *   page, `/guides/<slug>` (sync creates one per such tag), and is outlined.
+ *   `tagTarget()` picks the route (and between two landings, e.g. DFS); the
+ *   `PageFooter` backlinks list reads the same answer. Each tag badge is a
+ *   pill carrying the icon its target shows in the sidebar (the topic's
+ *   `meta.ts` icon, the guide's `icon:`) and the tag's own colour
+ *   (`lib/tag-colors.ts`), assigned over every tag the site has a page for —
+ *   no two tags share one, and tags that share problem pages are spread
+ *   furthest apart. A tag with no page (the LeetCode-list fallback) stays
+ *   gray and iconless.
+ * - `video:` (problem pages, written by `apps/cli/videos.ts`) is the NeetCode
+ *   walkthrough's YouTube id, the red "Explanation" badge at the end of the row.
+ * - `list:` (guide pages, written by sync on create) is the tag's LeetCode
+ *   problem list, an orange "LeetCode list" badge.
+ */
+import { getEntry } from "astro:content";
+import data from "blume:data";
+import Badge from "blume/components/content/Badge.astro";
+import { stripBase, withBase } from "blume/components/islands/base-path.ts";
+import { tagColors } from "../lib/tag-colors.ts";
+import { TOPIC_LANDINGS, tagTarget, type TopicTag } from "../topic-landings.ts";
+
+// `/sub/tree-dfs/invert-binary-tree/` (or `.../index.html` in a static build)
+// -> `/tree-dfs/invert-binary-tree`, the base-less shape of `data.routes`.
+const route =
+  stripBase(import.meta.env.BASE_URL ?? "/", Astro.url.pathname)
+    .replace(/(\/index)?\.html$/u, "")
+    .replace(/(.)\/+$/u, "$1");
+const at = data.routes.find((r: { path: string }) => r.path === route);
+const entry = at ? await getEntry(at.collection, at.entryId) : undefined;
+const tags: TopicTag[] = entry?.data.topics ?? [];
+const video: string | undefined = entry?.data.video;
+const list: string | undefined = entry?.data.list;
+
+const served = new Set<string>(data.routes.map((r: { path: string }) => r.path));
+
+// route → the icon its sidebar row shows: a page's own, or a topic group's
+// (from its `meta.ts`) for the landing page the group row links to.
+interface NavNode {
+  route?: string;
+  icon?: string;
+  children?: NavNode[];
+}
+const icons = new Map<string, string>();
+const walk = (nodes: NavNode[]) => {
+  for (const node of nodes) {
+    if (node.route && node.icon && !icons.has(node.route)) icons.set(node.route, node.icon);
+    if (node.children) walk(node.children);
+  }
+};
+walk(data.navigation.sidebar);
+
+// Every tag with a page — the ones a landing teaches, plus every served guide —
+// coloured against how problem pages (`<num>. <name>` titles, the shape sync
+// writes) combine them. Only a page with tags needs the answer.
+const colors = tags.length
+  ? tagColors(
+      [
+        ...Object.keys(TOPIC_LANDINGS),
+        ...[...served].flatMap((path) => path.match(/^\/guides\/([^/]+)$/u)?.slice(1) ?? []),
+      ],
+      await Promise.all(
+        data.routes
+          .filter((r: { title: string }) => /^\d+\.\s/u.test(r.title))
+          .map(async (r: { collection: string; entryId: string }) => {
+            const page = await getEntry(r.collection, r.entryId);
+            return (page?.data.topics ?? []).map((t: TopicTag) => t.slug);
+          }),
+      ),
+    )
+  : new Map<string, string>();
+
+const badges = tags.map((tag) => {
+  const target = tagTarget(tag, { route, tags }, served);
+  const external = target.kind === "external";
+  return {
+    name: tag.name,
+    href: external ? target.href : withBase(target.href),
+    external,
+    icon: external ? undefined : icons.get(target.href),
+    color: external ? undefined : colors.get(tag.slug),
+    stroke: target.kind !== "landing",
+  };
+});
+
+const linkClass = "no-underline transition-opacity hover:opacity-80";
+---
+
+{
+  (badges.length > 0 || video || list) && (
+    <div class="not-prose mb-6 flex flex-wrap gap-1.5">
+      {badges.map((b) => (
+        <a
+          href={b.href}
+          target={b.external ? "_blank" : undefined}
+          rel={b.external ? "noopener" : undefined}
+          class={linkClass}
+        >
+          <Badge color={b.color} icon={b.icon} shape="pill" stroke={b.stroke}>
+            {b.name}
+          </Badge>
+        </a>
+      ))}
+      {video && (
+        <a href={`https://www.youtube.com/watch?v=${video}`} target="_blank" rel="noopener" class={linkClass}>
+          <Badge variant="danger" icon="youtube" shape="pill">
+            Explanation
+          </Badge>
+        </a>
+      )}
+      {list && (
+        <a href={list} target="_blank" rel="noopener" class={linkClass}>
+          <Badge variant="warning" icon="list" shape="pill">
+            LeetCode list
+          </Badge>
+        </a>
+      )}
+    </div>
+  )
+}
+
+<slot />

apps/docs/components/progress/shared.tsx

@@ -0,0 +1,67 @@
+/**
+ * What the four progress islands share besides the data: the not-ready body
+ * (a skeleton while /api/stats loads, one muted line if it fails) and the
+ * hover tooltip for the two charts drawn as plain SVG (the heatmap calendar
+ * and the topic bubbles — Recharts has neither layout). The tooltip wears the
+ * exact classes of shadcn's ChartTooltipContent, so all four cards' tooltips
+ * look like one component.
+ */
+import { type PointerEvent, type ReactNode, useRef, useState } from "react";
+import { cn } from "../../lib/utils";
+import type { Load } from "../../lib/stats";
+import { Skeleton } from "../ui/skeleton";
+
+export function StatsPending({ load, className }: { load: Exclude<Load, { phase: "ready" }>; className: string }) {
+  if (load.phase === "loading") return <Skeleton className={className} />;
+  return (
+    <p className="my-0! text-muted-foreground text-sm">
+      Stats unavailable — they are served live from the SRS Worker, and it did not respond.
+    </p>
+  );
+}
+
+interface Tip {
+  x: number;
+  y: number;
+  content: ReactNode;
+}
+
+/**
+ * A pointer-following tooltip for SVG marks. Put `ref` on a `relative`
+ * wrapper, call `show` from a mark's pointer events, render `tip` inside the
+ * wrapper. Positions are relative to the wrapper, so page scroll never skews it.
+ */
+export function useHoverTip<T extends HTMLElement>() {
+  const ref = useRef<T>(null);
+  const [tip, setTip] = useState<Tip | null>(null);
+  const show = (event: PointerEvent, content: ReactNode) => {
+    const box = ref.current?.getBoundingClientRect();
+    if (box) setTip({ x: event.clientX - box.left, y: event.clientY - box.top, content });
+  };
+  const hide = () => setTip(null);
+  const node = tip && (
+    <div
+      className={cn(
+        "pointer-events-none absolute z-10 grid min-w-[8rem] -translate-x-1/2 -translate-y-[calc(100%+0.75rem)] items-start gap-1.5",
+        "rounded-lg border border-border/50 bg-background px-2.5 py-1.5 text-xs shadow-xl",
+      )}
+      style={{ left: tip.x, top: tip.y }}
+    >
+      {tip.content}
+    </div>
+  );
+  return { ref, show, hide, node };
+}
+
+/** One tooltip row, the shape ChartTooltipContent draws: colour dot, label, mono value. */
+export function TipRow({ color, label, value }: { color: string; label: ReactNode; value: ReactNode }) {
+  return (
+    <div className="flex w-full items-center gap-2">
+      <div className="size-2.5 shrink-0 rounded-[2px]" style={{ background: color }} />
+      <div className="flex flex-1 items-center justify-between gap-4 leading-none">
+        <span className="text-muted-foreground">{label}</span>
+        <span className="font-medium font-mono text-foreground tabular-nums">{value}</span>
+      </div>
+    </div>
+  );
+}

apps/docs/components/ui/card.tsx

@@ -0,0 +1,91 @@
+import * as React from "react"
+import { cn } from "../../lib/utils"
+
+function Card({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="card"
+      className={cn(
+        "flex flex-col gap-6 rounded-xl border bg-card py-6 text-card-foreground shadow-sm",
+        className
+      )}
+      {...props}
+    />
+  )
+}
+
+function CardHeader({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="card-header"
+      className={cn(
+        "@container/card-header grid auto-rows-min grid-rows-[auto_auto] items-start gap-2 px-6 has-data-[slot=card-action]:grid-cols-[1fr_auto] [.border-b]:pb-6",
+        className
+      )}
+      {...props}
+    />
+  )
+}
+
+function CardTitle({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="card-title"
+      className={cn("leading-none font-semibold", className)}
+      {...props}
+    />
+  )
+}
+
+function CardDescription({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="card-description"
+      className={cn("text-sm text-muted-foreground", className)}
+      {...props}
+    />
+  )
+}
+
+function CardAction({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="card-action"
+      className={cn(
+        "col-start-2 row-span-2 row-start-1 self-start justify-self-end",
+        className
+      )}
+      {...props}
+    />
+  )
+}
+
+function CardContent({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="card-content"
+      className={cn("px-6", className)}
+      {...props}
+    />
+  )
+}
+
+function CardFooter({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="card-footer"
+      className={cn("flex items-center px-6 [.border-t]:pt-6", className)}
+      {...props}
+    />
+  )
+}
+
+export {
+  Card,
+  CardHeader,
+  CardFooter,
+  CardTitle,
+  CardAction,
+  CardDescription,
+  CardContent,
+}

apps/docs/components/ui/chart.tsx

@@ -0,0 +1,372 @@
+import * as React from "react"
+import { cn } from "../../lib/utils"
+import * as RechartsPrimitive from "recharts"
+import type { TooltipValueType } from "recharts"
+
+// Format: { THEME_NAME: CSS_SELECTOR }. Blume switches dark mode with
+// [data-theme="dark"] on <html>, not shadcn's .dark class.
+const THEMES = { light: "", dark: ':root[data-theme="dark"]' } as const
+
+const INITIAL_DIMENSION = { width: 320, height: 200 } as const
+type TooltipNameType = number | string
+
+export type ChartConfig = Record<
+  string,
+  {
+    label?: React.ReactNode
+    icon?: React.ComponentType
+  } & (
+    | { color?: string; theme?: never }
+    | { color?: never; theme: Record<keyof typeof THEMES, string> }
+  )
+>
+
+type ChartContextProps = {
+  config: ChartConfig
+}
+
+const ChartContext = React.createContext<ChartContextProps | null>(null)
+
+function useChart() {
+  const context = React.useContext(ChartContext)
+
+  if (!context) {
+    throw new Error("useChart must be used within a <ChartContainer />")
+  }
+
+  return context
+}
+
+function ChartContainer({
+  id,
+  className,
+  children,
+  config,
+  initialDimension = INITIAL_DIMENSION,
+  ...props
+}: React.ComponentProps<"div"> & {
+  config: ChartConfig
+  children: React.ComponentProps<
+    typeof RechartsPrimitive.ResponsiveContainer
+  >["children"]
+  initialDimension?: {
+    width: number
+    height: number
+  }
+}) {
+  const uniqueId = React.useId()
+  const chartId = `chart-${id ?? uniqueId.replace(/:/g, "")}`
+
+  return (
+    <ChartContext.Provider value={{ config }}>
+      <div
+        data-slot="chart"
+        data-chart={chartId}
+        className={cn(
+          "flex aspect-video justify-center text-xs [&_.recharts-cartesian-axis-tick_text]:fill-muted-foreground [&_.recharts-cartesian-grid_line[stroke='#ccc']]:stroke-border/50 [&_.recharts-curve.recharts-tooltip-cursor]:stroke-border [&_.recharts-dot[stroke='#fff']]:stroke-transparent [&_.recharts-layer]:outline-hidden [&_.recharts-polar-grid_[stroke='#ccc']]:stroke-border [&_.recharts-radial-bar-background-sector]:fill-muted [&_.recharts-rectangle.recharts-tooltip-cursor]:fill-muted [&_.recharts-reference-line_[stroke='#ccc']]:stroke-border [&_.recharts-sector]:outline-hidden [&_.recharts-sector[stroke='#fff']]:stroke-transparent [&_.recharts-surface]:outline-hidden",
+          className
+        )}
+        {...props}
+      >
+        <ChartStyle id={chartId} config={config} />
+        <RechartsPrimitive.ResponsiveContainer
+          initialDimension={initialDimension}
+        >
+          {children}
+        </RechartsPrimitive.ResponsiveContainer>
+      </div>
+    </ChartContext.Provider>
+  )
+}
+
+const ChartStyle = ({ id, config }: { id: string; config: ChartConfig }) => {
+  const colorConfig = Object.entries(config).filter(
+    ([, config]) => config.theme ?? config.color
+  )
+
+  if (!colorConfig.length) {
+    return null
+  }
+
+  return (
+    <style
+      dangerouslySetInnerHTML={{
+        __html: Object.entries(THEMES)
+          .map(
+            ([theme, prefix]) => `
+${prefix} [data-chart=${id}] {
+${colorConfig
+  .map(([key, itemConfig]) => {
+    const color =
+      itemConfig.theme?.[theme as keyof typeof itemConfig.theme] ??
+      itemConfig.color
+    return color ? `  --color-${key}: ${color};` : null
+  })
+  .join("\n")}
+}
+`
+          )
+          .join("\n"),
+      }}
+    />
+  )
+}
+
+const ChartTooltip = RechartsPrimitive.Tooltip
+
+function ChartTooltipContent({
+  active,
+  payload,
+  className,
+  indicator = "dot",
+  hideLabel = false,
+  hideIndicator = false,
+  label,
+  labelFormatter,
+  labelClassName,
+  formatter,
+  color,
+  nameKey,
+  labelKey,
+}: React.ComponentProps<typeof RechartsPrimitive.Tooltip> &
+  React.ComponentProps<"div"> & {
+    hideLabel?: boolean
+    hideIndicator?: boolean
+    indicator?: "line" | "dot" | "dashed"
+    nameKey?: string
+    labelKey?: string
+  } & Omit<
+    RechartsPrimitive.DefaultTooltipContentProps<
+      TooltipValueType,
+      TooltipNameType
+    >,
+    "accessibilityLayer"
+  >) {
+  const { config } = useChart()
+
+  const tooltipLabel = React.useMemo(() => {
+    if (hideLabel || !payload?.length) {
+      return null
+    }
+
+    const [item] = payload
+    const key = `${labelKey ?? item?.dataKey ?? item?.name ?? "value"}`
+    const itemConfig = getPayloadConfigFromPayload(config, item, key)
+    const value =
+      !labelKey && typeof label === "string"
+        ? (config[label]?.label ?? label)
+        : itemConfig?.label
+
+    if (labelFormatter) {
+      return (
+        <div className={cn("font-medium", labelClassName)}>
+          {labelFormatter(value, payload)}
+        </div>
+      )
+    }
+
+    if (!value) {
+      return null
+    }
+
+    return <div className={cn("font-medium", labelClassName)}>{value}</div>
+  }, [
+    label,
+    labelFormatter,
+    payload,
+    hideLabel,
+    labelClassName,
+    config,
+    labelKey,
+  ])
+
+  if (!active || !payload?.length) {
+    return null
+  }
+
+  const nestLabel = payload.length === 1 && indicator !== "dot"
+
+  return (
+    <div
+      className={cn(
+        "grid min-w-[8rem] items-start gap-1.5 rounded-lg border border-border/50 bg-background px-2.5 py-1.5 text-xs shadow-xl",
+        className
+      )}
+    >
+      {!nestLabel ? tooltipLabel : null}
+      <div className="grid gap-1.5">
+        {payload
+          .filter((item) => item.type !== "none")
+          .map((item, index) => {
+            const key = `${nameKey ?? item.name ?? item.dataKey ?? "value"}`
+            const itemConfig = getPayloadConfigFromPayload(config, item, key)
+            const indicatorColor = color ?? item.payload?.fill ?? item.color
+
+            return (
+              <div
+                key={index}
+                className={cn(
+                  "flex w-full flex-wrap items-stretch gap-2 [&>svg]:h-2.5 [&>svg]:w-2.5 [&>svg]:text-muted-foreground",
+                  indicator === "dot" && "items-center"
+                )}
+              >
+                {formatter && item?.value !== undefined && item.name ? (
+                  formatter(item.value, item.name, item, index, item.payload)
+                ) : (
+                  <>
+                    {itemConfig?.icon ? (
+                      <itemConfig.icon />
+                    ) : (
+                      !hideIndicator && (
+                        <div
+                          className={cn(
+                            "shrink-0 rounded-[2px] border-(--color-border) bg-(--color-bg)",
+                            {
+                              "h-2.5 w-2.5": indicator === "dot",
+                              "w-1": indicator === "line",
+                              "w-0 border-[1.5px] border-dashed bg-transparent":
+                                indicator === "dashed",
+                              "my-0.5": nestLabel && indicator === "dashed",
+                            }
+                          )}
+                          style={
+                            {
+                              "--color-bg": indicatorColor,
+                              "--color-border": indicatorColor,
+                            } as React.CSSProperties
+                          }
+                        />
+                      )
+                    )}
+                    <div
+                      className={cn(
+                        "flex flex-1 justify-between leading-none",
+                        nestLabel ? "items-end" : "items-center"
+                      )}
+                    >
+                      <div className="grid gap-1.5">
+                        {nestLabel ? tooltipLabel : null}
+                        <span className="text-muted-foreground">
+                          {itemConfig?.label ?? item.name}
+                        </span>
+                      </div>
+                      {item.value != null && (
+                        <span className="font-mono font-medium text-foreground tabular-nums">
+                          {typeof item.value === "number"
+                            ? item.value.toLocaleString()
+                            : String(item.value)}
+                        </span>
+                      )}
+                    </div>
+                  </>
+                )}
+              </div>
+            )
+          })}
+      </div>
+    </div>
+  )
+}
+
+const ChartLegend = RechartsPrimitive.Legend
+
+function ChartLegendContent({
+  className,
+  hideIcon = false,
+  payload,
+  verticalAlign = "bottom",
+  nameKey,
+}: React.ComponentProps<"div"> & {
+  hideIcon?: boolean
+  nameKey?: string
+} & RechartsPrimitive.DefaultLegendContentProps) {
+  const { config } = useChart()
+
+  if (!payload?.length) {
+    return null
+  }
+
+  return (
+    <div
+      className={cn(
+        "flex items-center justify-center gap-4",
+        verticalAlign === "top" ? "pb-3" : "pt-3",
+        className
+      )}
+    >
+      {payload
+        .filter((item) => item.type !== "none")
+        .map((item, index) => {
+          const key = `${nameKey ?? item.dataKey ?? "value"}`
+          const itemConfig = getPayloadConfigFromPayload(config, item, key)
+
+          return (
+            <div
+              key={index}
+              className={cn(
+                "flex items-center gap-1.5 [&>svg]:h-3 [&>svg]:w-3 [&>svg]:text-muted-foreground"
+              )}
+            >
+              {itemConfig?.icon && !hideIcon ? (
+                <itemConfig.icon />
+              ) : (
+                <div
+                  className="h-2 w-2 shrink-0 rounded-[2px]"
+                  style={{
+                    backgroundColor: item.color,
+                  }}
+                />
+              )}
+              {itemConfig?.label}
+            </div>
+          )
+        })}
+    </div>
+  )
+}
+
+// Helper to extract item config from a payload.
+function getPayloadConfigFromPayload(
+  config: ChartConfig,
+  payload: unknown,
+  key: string
+) {
+  if (typeof payload !== "object" || payload === null) {
+    return undefined
+  }
+
+  const payloadPayload =
+    "payload" in payload &&
+    typeof payload.payload === "object" &&
+    payload.payload !== null
+      ? payload.payload
+      : undefined
+
+  let configLabelKey: string = key
+
+  if (
+    key in payload &&
+    typeof payload[key as keyof typeof payload] === "string"
+  ) {
+    configLabelKey = payload[key as keyof typeof payload] as string
+  } else if (
+    payloadPayload &&
+    key in payloadPayload &&
+    typeof payloadPayload[key as keyof typeof payloadPayload] === "string"
+  ) {
+    configLabelKey = payloadPayload[
+      key as keyof typeof payloadPayload
+    ] as string
+  }
+
+  return configLabelKey in config ? config[configLabelKey] : config[key]
+}
+
+export {
+  ChartContainer,
+  ChartTooltip,
+  ChartTooltipContent,
+  ChartLegend,
+  ChartLegendContent,
+  ChartStyle,
+}

apps/docs/components/ui/skeleton.tsx

@@ -0,0 +1,13 @@
+import { cn } from "../../lib/utils"
+
+function Skeleton({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="skeleton"
+      className={cn("animate-pulse rounded-md bg-muted", className)}
+      {...props}
+    />
+  )
+}
+
+export { Skeleton }

apps/docs/components/ui/toggle-group.tsx

@@ -0,0 +1,83 @@
+"use client"
+
+import * as React from "react"
+import { type VariantProps } from "class-variance-authority"
+import { cn } from "../../lib/utils"
+import { ToggleGroup as ToggleGroupPrimitive } from "radix-ui"
+
+import { toggleVariants } from "./toggle"
+
+const ToggleGroupContext = React.createContext<
+  VariantProps<typeof toggleVariants> & {
+    spacing?: number
+  }
+>({
+  size: "default",
+  variant: "default",
+  spacing: 0,
+})
+
+function ToggleGroup({
+  className,
+  variant,
+  size,
+  spacing = 0,
+  children,
+  ...props
+}: React.ComponentProps<typeof ToggleGroupPrimitive.Root> &
+  VariantProps<typeof toggleVariants> & {
+    spacing?: number
+  }) {
+  return (
+    <ToggleGroupPrimitive.Root
+      data-slot="toggle-group"
+      data-variant={variant}
+      data-size={size}
+      data-spacing={spacing}
+      style={{ "--gap": spacing } as React.CSSProperties}
+      className={cn(
+        "group/toggle-group flex w-fit items-center gap-[--spacing(var(--gap))] rounded-md data-[spacing=default]:data-[variant=outline]:shadow-xs",
+        className
+      )}
+      {...props}
+    >
+      <ToggleGroupContext.Provider value={{ variant, size, spacing }}>
+        {children}
+      </ToggleGroupContext.Provider>
+    </ToggleGroupPrimitive.Root>
+  )
+}
+
+function ToggleGroupItem({
+  className,
+  children,
+  variant,
+  size,
+  ...props
+}: React.ComponentProps<typeof ToggleGroupPrimitive.Item> &
+  VariantProps<typeof toggleVariants>) {
+  const context = React.useContext(ToggleGroupContext)
+
+  return (
+    <ToggleGroupPrimitive.Item
+      data-slot="toggle-group-item"
+      data-variant={context.variant || variant}
+      data-size={context.size || size}
+      data-spacing={context.spacing}
+      className={cn(
+        toggleVariants({
+          variant: context.variant || variant,
+          size: context.size || size,
+        }),
+        "w-auto min-w-0 shrink-0 px-3 focus:z-10 focus-visible:z-10",
+        "data-[spacing=0]:rounded-none data-[spacing=0]:shadow-none data-[spacing=0]:first:rounded-l-md data-[spacing=0]:last:rounded-r-md data-[spacing=0]:data-[variant=outline]:border-l-0 data-[spacing=0]:data-[variant=outline]:first:border-l",
+        className
+      )}
+      {...props}
+    >
+      {children}
+    </ToggleGroupPrimitive.Item>
+  )
+}
+
+export { ToggleGroup, ToggleGroupItem }

apps/docs/components/ui/toggle.tsx

@@ -0,0 +1,47 @@
+import * as React from "react"
+import { cva, type VariantProps } from "class-variance-authority"
+import { cn } from "../../lib/utils"
+import { Toggle as TogglePrimitive } from "radix-ui"
+
+// Blume's `accent` is its brand colour, not shadcn's subtle surface: the on
+// and hover states use background/muted instead (see theme.css).
+
+const toggleVariants = cva(
+  "inline-flex items-center justify-center gap-2 rounded-md text-sm font-medium whitespace-nowrap transition-[color,box-shadow] outline-none hover:bg-muted hover:text-muted-foreground focus-visible:border-ring focus-visible:ring-[3px] focus-visible:ring-ring/50 disabled:pointer-events-none disabled:opacity-50 aria-invalid:border-destructive aria-invalid:ring-destructive/20 data-[state=on]:bg-background data-[state=on]:text-foreground data-[state=on]:shadow-sm dark:aria-invalid:ring-destructive/40 [&_svg]:pointer-events-none [&_svg]:shrink-0 [&_svg:not([class*='size-'])]:size-4",
+  {
+    variants: {
+      variant: {
+        default: "bg-transparent",
+        outline:
+          "border border-input bg-transparent shadow-xs hover:bg-muted hover:text-foreground",
+      },
+      size: {
+        default: "h-9 min-w-9 px-2",
+        sm: "h-8 min-w-8 px-1.5",
+        lg: "h-10 min-w-10 px-2.5",
+      },
+    },
+    defaultVariants: {
+      variant: "default",
+      size: "default",
+    },
+  }
+)
+
+function Toggle({
+  className,
+  variant,
+  size,
+  ...props
+}: React.ComponentProps<typeof TogglePrimitive.Root> &
+  VariantProps<typeof toggleVariants>) {
+  return (
+    <TogglePrimitive.Root
+      data-slot="toggle"
+      className={cn(toggleVariants({ variant, size, className }))}
+      {...props}
+    />
+  )
+}
+
+export { Toggle, toggleVariants }

apps/docs/content/(01-linear-structures)/binary-search/153-find-minimum-in-rotated-sorted-array.mdx

@@ -1,13 +1,16 @@
 ---
 title: '153. Find Minimum in Rotated Sorted Array'
 description: 'Suppose an array of length n sorted in ascending order is rotated between 1 and n times. For example, the array nums = [0,1,2,4,5,6,7] might become:'
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Binary Search", slug: "binary-search" }
+video: "nIVW4P8b1VA"
 sidebar:
   label: 'Find Minimum in Rotated Sorted Array'
   badge: 'Medium'
 ---
 
-<Badge variant="accent">Binary Search</Badge>
-
 ::::warning
 Notice that rotating an array [a[0], a[1], a[2], ..., a[n-1]] 1 time results in the array [a[n-1], a[0], a[1], a[2], ..., a[n-2]].
 ::::
@@ -35,6 +38,21 @@ Notice that rotating an array [a[0], a[1], a[2], ..., a[n-1]] 1 time results in
 - All the integers of `nums` are unique.
 - `nums` is sorted and rotated between 1 and `n` times.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["findMin(nums)"]) --> I["l = 0, r = n-1, lowest_index = -1"]
+  I --> W{"l <= r?"}
+  W -- no --> E(["return nums[lowest_index]"])
+  W -- yes --> M["m = (l + r) // 2"]
+  M --> C{"nums[m] <= nums[-1]?"}
+  C -- yes --> A["in the right sorted run: record lowest_index = m, r = m - 1"]
+  A --> W
+  C -- no --> B["still in the left sorted run: l = m + 1"]
+  B --> W
+```
+
 ## Solution
 
 ```py

apps/docs/content/(01-linear-structures)/binary-search/33-search-in-rotated-sorted-array.mdx

@@ -1,13 +1,16 @@
 ---
 title: '33. Search in Rotated Sorted Array'
 description: There is an integer array nums sorted in ascending order (with distinct values)
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Binary Search", slug: "binary-search" }
+video: "U8XENwh8Oy8"
 sidebar:
   label: 'Search in Rotated Sorted Array'
   badge: 'Medium'
 ---
 
-<Badge variant="accent">Binary Search</Badge>
-
 ::::warning
 You must write an algorithm with O(log n) runtime complexity.
 ::::
@@ -32,6 +35,29 @@ You must write an algorithm with O(log n) runtime complexity.
 - `nums` is an ascending array that is possibly rotated.
 - `-10^4 <= target <= 10^4`
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["search(nums, target)"]) --> I["l = 0, r = n - 1"]
+  I --> W{"l <= r?"}
+  W -- no --> E(["return -1"])
+  W -- yes --> M["mid = floor((l + r) / 2)"]
+  M --> F{"nums[mid] == target?"}
+  F -- yes --> R(["return mid"])
+  F -- no --> H{"nums[l] <= nums[mid]? — left half sorted"}
+  H -- yes --> A{"target outside [nums[l], nums[mid]]?"}
+  A -- yes --> A1["l = mid + 1 — search the right half"]
+  A -- no --> A2["r = mid - 1"]
+  H -- no --> B{"target outside [nums[mid], nums[r]]?"}
+  B -- yes --> B1["r = mid - 1 — search the left half"]
+  B -- no --> B2["l = mid + 1"]
+  A1 --> W
+  A2 --> W
+  B1 --> W
+  B2 --> W
+```
+
 ## Solution
 
 ```js

apps/docs/content/(01-linear-structures)/binary-search/35-search-insert-position.mdx

@@ -1,13 +1,16 @@
 ---
 title: '35. Search Insert Position'
 description: Given a sorted array of distinct integers and a target value, return the index if the target is found. If not, return the index where it would be if it were inserted in order
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Binary Search", slug: "binary-search" }
+video: "K-RYzDZkzCI"
 sidebar:
   label: 'Search Insert Position'
   badge: 'Easy'
 ---
 
-<Badge variant="accent">Binary Search</Badge>
-
 ::::warning
 You must write an algorithm with O(log n) runtime complexity.
 ::::
@@ -31,6 +34,22 @@ You must write an algorithm with O(log n) runtime complexity.
 - `nums` contains distinct values sorted in ascending order.
 - `-10^4 <= target <= 10^4`
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["searchInsert(nums, target)"]) --> I["l = 0, r = n - 1"]
+  I --> W{"l <= r?"}
+  W -- yes --> M["m = (l + r) // 2"]
+  M --> Q{"nums[m] vs target"}
+  Q -- equal --> R(["return m"])
+  Q -- "nums[m] < target" --> L["l = m + 1"]
+  L --> W
+  Q -- "nums[m] > target" --> H["r = m - 1"]
+  H --> W
+  W -- no --> E(["return (l + r) // 2 + 1 — the insert slot"])
+```
+
 ## Solution
 
 ```py

apps/docs/content/(01-linear-structures)/binary-search/704-binary-search.mdx

@@ -1,13 +1,16 @@
 ---
 title: '704. Binary Search'
 description: Given an array of integers nums which is sorted in ascending order, and an integer target, write a function to search target in nums. If target exists, then return its index. Otherwise, return -1
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Binary Search", slug: "binary-search" }
+video: "s4DPM8ct1pI"
 sidebar:
   label: 'Binary Search'
   badge: 'Easy'
 ---
 
-<Badge variant="accent">Binary Search</Badge>
-
 ::::warning
 You must write an algorithm with O(log n) runtime complexity.
 ::::
@@ -29,6 +32,22 @@ You must write an algorithm with O(log n) runtime complexity.
 - All the integers in `nums` are unique.
 - `nums` is sorted in ascending order.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["search(nums, target)"]) --> I["left = 0, right = n - 1"]
+  I --> W{"left <= right?"}
+  W -- no --> E(["return -1"])
+  W -- yes --> M["mid = left + floor((right - left) / 2)"]
+  M --> Q{"nums[mid] vs target"}
+  Q -- equal --> R(["return mid"])
+  Q -- "nums[mid] < target" --> L["left = mid + 1"]
+  L --> W
+  Q -- "nums[mid] > target" --> H["right = mid - 1"]
+  H --> W
+```
+
 ## Solution
 
 ```js

apps/docs/content/(01-linear-structures)/binary-search/74-search-a-2d-matrix.mdx

@@ -1,13 +1,17 @@
 ---
 title: '74. Search a 2D Matrix'
 description: 'You are given an m x n integer matrix matrix with the following two properties:'
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Binary Search", slug: "binary-search" }
+  - { name: "Matrix", slug: "matrix" }
+video: "Ber2pi2C0j0"
 sidebar:
   label: 'Search a 2D Matrix'
   badge: 'Medium'
 ---
 
-<Badge variant="accent">Binary Search</Badge>
-
 ::::warning
 You must write a solution in O(log(m * n)) time complexity.
 ::::
@@ -27,6 +31,32 @@ You must write a solution in O(log(m * n)) time complexity.
 - `1 <= m, n <= 100`
 - `-10^4 <= matrix[i][j], target <= 10^4`
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["searchMatrix(matrix, target)"]) --> I["top = 0, bot = ROWS - 1"]
+  I --> W1{"top <= bot?"}
+  W1 -- yes --> R1["row = (top + bot) // 2"]
+  R1 --> C1{"target vs that row's range"}
+  C1 -- "above matrix[row][-1]" --> U["top = row + 1"]
+  C1 -- "below matrix[row][0]" --> V["bot = row - 1"]
+  C1 -- inside --> B(["break — row found"])
+  U --> W1
+  V --> W1
+  W1 -- no --> F(["return False — no row can hold it"])
+  B --> P["row = (top + bot) // 2; l = 0, r = COLS - 1"]
+  P --> W2{"l <= r?"}
+  W2 -- no --> G(["return False"])
+  W2 -- yes --> M["m = (l + r) // 2"]
+  M --> C2{"target vs matrix[row][m]"}
+  C2 -- greater --> X["l = m + 1"]
+  C2 -- smaller --> Y["r = m - 1"]
+  C2 -- equal --> T(["return True"])
+  X --> W2
+  Y --> W2
+```
+
 ## Solution
 
 ```py

apps/docs/content/(01-linear-structures)/binary-search/875-koko-eating-bananas.mdx

@@ -1,13 +1,16 @@
 ---
 title: '875. Koko Eating Bananas'
 description: Koko loves to eat bananas. There are n piles of bananas, the i^th pile has piles[i] bananas. The guards have gone and will come back in h hours
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Binary Search", slug: "binary-search" }
+video: "U2SozAs9RzA"
 sidebar:
   label: 'Koko Eating Bananas'
   badge: 'Medium'
 ---
 
-<Badge variant="accent">Binary Search</Badge>
-
 ### Example 1:
 - Input: `piles = [3,6,7,11], h = 8`
 - Output: `4`
@@ -26,6 +29,22 @@ sidebar:
 - `piles.length <= h <= 10^9`
 - `1 <= piles[i] <= 10^9`
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["minEatingSpeed(piles, h)"]) --> I["l = 1, r = max(piles)"]
+  I --> W{"l < r?"}
+  W -- no --> E(["return l — the smallest workable speed"])
+  W -- yes --> M["mid = floor((l + r) / 2)"]
+  M --> K["kWorks(mid): hours = sum of ceil(p / mid)"]
+  K --> Q{"hours <= h?"}
+  Q -- yes --> A["r = mid — keep mid, try slower"]
+  Q -- no --> B["l = mid + 1 — too slow, speed up"]
+  A --> W
+  B --> W
+```
+
 ## Solution
 
 ```js

apps/docs/content/(01-linear-structures)/binary-search/index.mdx

@@ -0,0 +1,5 @@
+---
+title: Binary Search
+description: 'Half of a sorted range is removed at each step until the target is found.'
+hidden: true
+---

apps/docs/content/(01-linear-structures)/binary-search/meta.ts

@@ -0,0 +1,8 @@
+import { defineMeta } from "blume";
+
+export default defineMeta({
+  title: "Binary Search",
+  order: 5,
+  icon: "search",
+  display: "group",
+});

apps/docs/content/(01-linear-structures)/hash-table/1-two-sum.mdx

@@ -1,13 +1,16 @@
 ---
 title: '1. Two Sum'
 description: You are given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Hash Table", slug: "hash-table" }
+video: "KLlXCFG5TnA"
 sidebar:
   label: 'Two Sum'
   badge: 'Easy'
 ---
 
-<Badge variant="accent">Hash Table</Badge>
-
 ::::warning
 Can you come up with an algorithm that is less than O(n^2) time complexity?
 ::::
@@ -32,6 +35,20 @@ Can you come up with an algorithm that is less than O(n^2) time complexity?
 - `-10^9 <= target <= 10^9`
 - Only one valid answer exists.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["twoSum(nums, target)"]) --> I["seen = {} — value to index"]
+  I --> L{"more (i, num) in nums?"}
+  L -- no --> E(["return []"])
+  L -- yes --> C["complement = target - num"]
+  C --> H{"complement in seen?"}
+  H -- yes --> R(["return [seen[complement], i]"])
+  H -- no --> W["seen[num] = i"]
+  W --> L
+```
+
 ## Solution
 
 ```py

apps/docs/content/(01-linear-structures)/hash-table/1832-check-if-the-sentence-is-pangram.mdx

@@ -1,13 +1,15 @@
 ---
 title: '1832. Check if the Sentence Is Pangram'
 description: A pangram is a sentence where every letter of the English alphabet appears at least once
+icon: dot
+topics:
+  - { name: "Hash Table", slug: "hash-table" }
+  - { name: "String", slug: "string" }
 sidebar:
   label: 'Check if the Sentence Is Pangram'
   badge: 'Easy'
 ---
 
-<Badge variant="accent">Hash Table</Badge>
-
 ### Example 1:
 - Input: `sentence = "thequickbrownfoxjumpsoverthelazydog"`
 - Output: `true`
@@ -22,6 +24,19 @@ sidebar:
 - `1 <= sentence.length <= 1000`
 - `sentence` consists of lowercase English letters.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["checkIfPangram(sentence)"]) --> I["freq = {}"]
+  I --> L{"more char c?"}
+  L -- yes --> C["freq[c] = (freq[c] or 0) + 1"]
+  C --> L
+  L -- no --> Q{"distinct keys in freq == 26?"}
+  Q -- yes --> R(["return true"])
+  Q -- no --> F(["return false"])
+```
+
 ## Solution
 
 ```js

apps/docs/content/(01-linear-structures)/hash-table/217-contains-duplicate.mdx

@@ -1,13 +1,17 @@
 ---
 title: '217. Contains Duplicate'
 description: Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Hash Table", slug: "hash-table" }
+  - { name: "Sorting", slug: "sorting" }
+video: "3OamzN90kPg"
 sidebar:
   label: 'Contains Duplicate'
   badge: 'Easy'
 ---
 
-<Badge variant="accent">Hash Table</Badge>
-
 ### Example 1:
 - Input: `nums = [1,2,3,1]`
 - Output: `true`
@@ -27,21 +31,23 @@ sidebar:
 - `1 <= nums.length <= 10^5`
 - `-10^9 <= nums[i] <= 10^9`
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["containsDuplicate(nums)"]) --> I["freq = {}"]
+  I --> L{"more n in nums?"}
+  L -- no --> E(["return false"])
+  L -- yes --> C["freq[n] = (freq[n] or 0) + 1"]
+  C --> Q{"freq[n] >= 2?"}
+  Q -- yes --> R(["return true"])
+  Q -- no --> L
+```
+
 ## Solution
 
-```js
-/**
- * @param {number[]} nums
- * @return {boolean}
- */
-var containsDuplicate = function(nums) {
-  const freq = {};
-  for (let n of nums) {
-    freq[n] = (freq[n] || 0) + 1;
-    if (freq[n] >= 2) {
-      return true;
-    }
-  } 
-  return false;
-};
+```py
+class Solution:
+    def containsDuplicate(self, nums: List[int]) -> bool:
+        return len(set(nums)) != len(nums)
 ```

apps/docs/content/(01-linear-structures)/hash-table/242-valid-anagram.mdx

@@ -1,13 +1,17 @@
 ---
 title: '242. Valid Anagram'
 description: Given two strings s and t, return true if t is an anagram of s, and false otherwise
+icon: dot
+topics:
+  - { name: "Hash Table", slug: "hash-table" }
+  - { name: "String", slug: "string" }
+  - { name: "Sorting", slug: "sorting" }
+video: "9UtInBqnCgA"
 sidebar:
   label: 'Valid Anagram'
   badge: 'Easy'
 ---
 
-<Badge variant="accent">Hash Table</Badge>
-
 ::::warning
 What if the inputs contain Unicode characters? How would you adapt your solution to such a case?
 ::::
@@ -25,6 +29,19 @@ What if the inputs contain Unicode characters? How would you adapt your solution
 - `1 <= s.length, t.length <= 5 * 10^4`
 - `s` and `t` consist of lowercase English letters.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["isAnagram(s, t)"]) --> I["freq: count every char of s"]
+  I --> L{"more char c in t?"}
+  L -- no --> E(["return true"])
+  L -- yes --> Q{"freq[c] missing or 0?"}
+  Q -- yes --> R(["return false — t has a char s cannot cover"])
+  Q -- no --> D["freq[c] -= 1"]
+  D --> L
+```
+
 ## Solution
 
 ```js

apps/docs/content/(01-linear-structures)/hash-table/347-top-k-frequent-elements.mdx

@@ -1,13 +1,22 @@
 ---
 title: '347. Top K Frequent Elements'
 description: Given an integer array nums and an integer k, return the k most frequent elements. You may return the answer in any order
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Hash Table", slug: "hash-table" }
+  - { name: "Divide and Conquer", slug: "divide-and-conquer" }
+  - { name: "Sorting", slug: "sorting" }
+  - { name: "Heap (Priority Queue)", slug: "heap-priority-queue" }
+  - { name: "Bucket Sort", slug: "bucket-sort" }
+  - { name: "Counting", slug: "counting" }
+  - { name: "Quickselect", slug: "quickselect" }
+video: "YPTqKIgVk-k"
 sidebar:
   label: 'Top K Frequent Elements'
   badge: 'Medium'
 ---
 
-<Badge variant="accent">Hash Table</Badge>
-
 ::::warning
 Your algorithm's time complexity must be better than O(n log n), where n is the array's size.
 ::::
@@ -31,6 +40,16 @@ Your algorithm's time complexity must be better than O(n log n), where n is the
 - `k` is in the range `[1, the number of unique elements in the array]`.
 - It is guaranteed that the answer is unique.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["topKFrequent(nums, k)"]) --> F["freq: count every value in nums"]
+  F --> K["keys of freq, cast to Number"]
+  K --> O["sort by freq[b] - freq[a] — most frequent first"]
+  O --> R(["return slice(0, k)"])
+```
+
 ## Solution
 
 ```js

apps/docs/content/(01-linear-structures)/hash-table/387-first-unique-character-in-a-string.mdx

@@ -1,13 +1,18 @@
 ---
 title: '387. First Unique Character in a String'
 description: Given a string s, find the first non-repeating character in it and return its index. If it does not exist, return -1
+icon: dot
+topics:
+  - { name: "Hash Table", slug: "hash-table" }
+  - { name: "String", slug: "string" }
+  - { name: "Queue", slug: "queue" }
+  - { name: "Counting", slug: "counting" }
+video: "rBENYgWy3xU"
 sidebar:
   label: 'First Unique Character in a String'
   badge: 'Easy'
 ---
 
-<Badge variant="accent">Hash Table</Badge>
-
 ### Example 1:
 - Input: `s = "leetcode"`
 - Output: `0`
@@ -26,6 +31,18 @@ sidebar:
 - `1 <= s.length <= 10^5`
 - `s` consists of only lowercase English letters.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["firstUniqChar(s)"]) --> F["Pass 1 — freq: count every char of s"]
+  F --> L{"Pass 2 — more i in 0..len-1?"}
+  L -- no --> E(["return -1"])
+  L -- yes --> Q{"freq[s[i]] == 1?"}
+  Q -- yes --> R(["return i — leftmost wins because the scan is in order"])
+  Q -- no --> L
+```
+
 ## Solution
 
 ```js

apps/docs/content/(01-linear-structures)/hash-table/451-sort-characters-by-frequency.mdx

@@ -1,13 +1,20 @@
 ---
 title: '451. Sort Characters By Frequency'
 description: Given a string s, sort it in decreasing order based on the frequency of the characters. The frequency of a character is the number of times it appears in the string
+icon: dot
+topics:
+  - { name: "Hash Table", slug: "hash-table" }
+  - { name: "String", slug: "string" }
+  - { name: "Sorting", slug: "sorting" }
+  - { name: "Heap (Priority Queue)", slug: "heap-priority-queue" }
+  - { name: "Bucket Sort", slug: "bucket-sort" }
+  - { name: "Counting", slug: "counting" }
+video: "OXdXc9HTrIg"
 sidebar:
   label: 'Sort Characters By Frequency'
   badge: 'Medium'
 ---
 
-<Badge variant="accent">Hash Table</Badge>
-
 ### Example 1:
 - Input: `s = "tree"`
 - Output: `"eert"`
@@ -28,6 +35,18 @@ sidebar:
 - `1 <= s.length <= 5 * 10^5`
 - `s` consists of uppercase and lowercase English letters and digits.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["frequencySort(s)"]) --> F["freq: count every char of s"]
+  F --> C["split s and sort with a two-key comparator"]
+  C --> K1["primary: freq[b] - freq[a] — most frequent first"]
+  C --> K2["tie-break: a.localeCompare(b) — alphabetical"]
+  K1 --> R(["join and return"])
+  K2 --> R
+```
+
 ## Solution
 
 ```js

apps/docs/content/(01-linear-structures)/hash-table/49-group-anagrams.mdx

@@ -1,13 +1,18 @@
 ---
 title: '49. Group Anagrams'
 description: Given an array of strings strs, group the anagrams together. You can return the answer in any order
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Hash Table", slug: "hash-table" }
+  - { name: "String", slug: "string" }
+  - { name: "Sorting", slug: "sorting" }
+video: "vzdNOK2oB2E"
 sidebar:
   label: 'Group Anagrams'
   badge: 'Medium'
 ---
 
-<Badge variant="accent">Hash Table</Badge>
-
 ### Example 1:
 - Input: `strs = ["eat","tea","tan","ate","nat","bat"]`
 - Output: `[["bat"],["nat","tan"],["ate","eat","tea"]]`
@@ -27,6 +32,21 @@ sidebar:
 - `0 <= strs[i].length <= 100`
 - `strs[i]` consists of lowercase English letters.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["groupAnagrams(strs)"]) --> K["sorted[i] = letters of strs[i], sorted — the anagram key"]
+  K --> I["anagrams = {}"]
+  I --> L{"more i in 0..n-1?"}
+  L -- no --> E(["return Object.values(anagrams)"])
+  L -- yes --> Q{"anagrams has sorted[i]?"}
+  Q -- no --> N["anagrams[sorted[i]] = [strs[i]]"]
+  Q -- yes --> P["anagrams[sorted[i]].push(strs[i])"]
+  N --> L
+  P --> L
+```
+
 ## Solution
 
 ```js

apps/docs/content/(01-linear-structures)/hash-table/index.mdx

@@ -0,0 +1,5 @@
+---
+title: Hash Table
+description: 'A key maps to a value in constant time, which removes the need for a full scan.'
+hidden: true
+---

apps/docs/content/(01-linear-structures)/hash-table/meta.ts

@@ -0,0 +1,8 @@
+import { defineMeta } from "blume";
+
+export default defineMeta({
+  title: "Hash Table",
+  order: 1,
+  icon: "hash",
+  display: "group",
+});

apps/docs/content/(01-linear-structures)/meta.ts

@@ -0,0 +1,3 @@
+import { defineMeta } from "blume";
+
+export default defineMeta({ title: "1. Linear Structures", order: 1 });

apps/docs/content/(01-linear-structures)/monotonic-stack/739-daily-temperatures.mdx

@@ -1,13 +1,17 @@
 ---
 title: '739. Daily Temperatures'
 description: Given an array of integers temperatures represents the daily temperatures, return an array answer such that answer[i] is the number of days you have to wait after the i^th day to get a warmer temperature. If there is no future day for which this is possible, keep answer[i] == 0 instead
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Stack", slug: "stack" }
+  - { name: "Monotonic Stack", slug: "monotonic-stack" }
+video: "cTBiBSnjO3c"
 sidebar:
   label: 'Daily Temperatures'
   badge: 'Medium'
 ---
 
-<Badge variant="accent">Monotonic Stack</Badge>
-
 ### Example 1:
 - Input: `temperatures = [73,74,75,71,69,72,76,73]`
 - Output: `[1,1,4,2,1,1,0,0]`
@@ -25,6 +29,20 @@ sidebar:
 - `1 <= temperatures.length <= 10^5`
 - `30 <= temperatures[i] <= 100`
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["dailyTemperatures(temperatures)"]) --> I["ans = zeros(n), stack = [] — indices of days still waiting"]
+  I --> L{"more (i, temp)?"}
+  L -- no --> E(["return ans"])
+  L -- yes --> W{"stack non-empty and temperatures[stack[-1]] < temp?"}
+  W -- yes --> P["prev = stack.pop(); ans[prev] = i - prev — today resolves that day"]
+  P --> W
+  W -- no --> A["stack.append(i)"]
+  A --> L
+```
+
 ## Solution
 
 ```py

apps/docs/content/(01-linear-structures)/monotonic-stack/853-car-fleet.mdx

@@ -1,13 +1,18 @@
 ---
 title: '853. Car Fleet'
 description: There are n cars at given miles away from the starting mile 0, traveling to reach the mile target
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Stack", slug: "stack" }
+  - { name: "Sorting", slug: "sorting" }
+  - { name: "Monotonic Stack", slug: "monotonic-stack" }
+video: "Pr6T-3yB9RM"
 sidebar:
   label: 'Car Fleet'
   badge: 'Medium'
 ---
 
-<Badge variant="accent">Monotonic Stack</Badge>
-
 ### Example 1:
 - Input: `target = 12, position = [10,8,0,5,3], speed = [2,4,1,1,3]`
 - Output: `3`
@@ -32,6 +37,22 @@ sidebar:
 - All the values of `position` are unique.
 - `0 < speed[i] <= 10^6`
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["carFleet(target, position, speed)"]) --> O["zip and sort by position, descending — nearest the target first"]
+  O --> I["stack = [] — arrival time of each fleet's leader"]
+  I --> L{"more (pos, spd)?"}
+  L -- no --> E(["return len(stack) — one entry per fleet"])
+  L -- yes --> T["time = (target - pos) / spd"]
+  T --> Q{"stack empty or time > stack[-1]?"}
+  Q -- yes --> A["stack.append(time) — slower, so it starts a new fleet"]
+  Q -- no --> B["discard — it catches the car ahead and joins that fleet"]
+  A --> L
+  B --> L
+```
+
 ## Solution
 
 ```py

apps/docs/content/(01-linear-structures)/monotonic-stack/index.mdx

@@ -0,0 +1,5 @@
+---
+title: Monotonic Stack
+description: 'A stack keeps its items in sorted order, which finds the next larger or smaller item in one pass.'
+hidden: true
+---

apps/docs/content/(01-linear-structures)/monotonic-stack/meta.ts

@@ -0,0 +1,3 @@
+import { defineMeta } from "blume";
+
+export default defineMeta({ title: "Monotonic Stack", order: 7, icon: "trending-up", display: "group" });

apps/docs/content/(01-linear-structures)/prefix-sum/238-product-of-array-except-self.mdx

@@ -1,13 +1,16 @@
 ---
 title: '238. Product of Array Except Self'
 description: Given an integer array nums, return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i]
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Prefix Sum", slug: "prefix-sum" }
+video: "bNvIQI2wAjk"
 sidebar:
   label: 'Product of Array Except Self'
   badge: 'Medium'
 ---
 
-<Badge variant="accent">Prefix Sum</Badge>
-
 ::::warning
 You must write an algorithm that runs in O(n) time and without using the division operation.
 Can you solve the problem in O(1) extra space complexity? (The output array does not count as extra space for space complexity analysis.)
@@ -27,6 +30,17 @@ Can you solve the problem in O(1) extra space complexity? (The output array does
 - `-30 <= nums[i] <= 30`
 - The input is generated such that `answer[i]` is guaranteed to fit in a 32-bit integer.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["productExceptSelf(nums)"]) --> I["answer = ones(n), rightArr = ones(n)"]
+  I --> P1["Pass 1 — left to right: answer[i] = nums[i-1] * answer[i-1]"]
+  P1 --> P2["Pass 2 — right to left: rightArr[i] = nums[i+1] * rightArr[i+1]"]
+  P2 --> P3["Pass 3: answer[i] *= rightArr[i]"]
+  P3 --> E(["return answer — no division needed"])
+```
+
 ## Solution
 
 ```js

apps/docs/content/(01-linear-structures)/prefix-sum/303-range-sum-query-immutable.mdx

@@ -1,13 +1,17 @@
 ---
 title: '303. Range Sum Query - Immutable'
 description: Given an integer array nums, handle multiple queries of the following type
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Design", slug: "design" }
+  - { name: "Prefix Sum", slug: "prefix-sum" }
+video: "2pndAmo_sMA"
 sidebar:
   label: 'Range Sum Query - Immutable'
   badge: 'Easy'
 ---
 
-<Badge variant="accent">Prefix Sum</Badge>
-
 ### Example 1:
 - Input: `["NumArray", "sumRange", "sumRange", "sumRange"]` `[[[-2, 0, 3, -5, 2, -1]], [0, 2], [2, 5], [0, 5]]`
 - Output: `[null, 1, -1, -3]`
@@ -20,6 +24,21 @@ sidebar:
 - `0 <= left <= right < nums.length`
 - At most `10^4` calls will be made to `sumRange`.
 
+## Approach
+
+```mermaid
+flowchart TD
+  subgraph build["constructor(nums) — O(n) once"]
+    A["prefix = [0]"] --> B{"more n in nums?"}
+    B -- yes --> C["prefix.push(last + n)"]
+    C --> B
+  end
+  build --> Q
+  subgraph Q["sumRange(left, right) — O(1) per call"]
+    D(["return prefix[right + 1] - prefix[left]"])
+  end
+```
+
 ## Solution
 
 ```js

apps/docs/content/(01-linear-structures)/prefix-sum/560-subarray-sum-equals-k.mdx

@@ -1,13 +1,17 @@
 ---
 title: '560. Subarray Sum Equals K'
 description: Given an array of integers nums and an integer k, return the total number of subarrays whose sum equals to k
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Hash Table", slug: "hash-table" }
+  - { name: "Prefix Sum", slug: "prefix-sum" }
+video: "fFVZt-6sgyo"
 sidebar:
   label: 'Subarray Sum Equals K'
   badge: 'Medium'
 ---
 
-<Badge variant="accent">Prefix Sum</Badge>
-
 ### Example 1:
 - Input: `nums = [1,1,1], k = 2`
 - Output: `2`
@@ -22,6 +26,21 @@ sidebar:
 - `-1000 <= nums[i] <= 1000`
 - `-10^7 <= k <= 10^7`
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["subarraySum(nums, k)"]) --> I["map = {0: 1} — the empty prefix; sum = 0, count = 0"]
+  I --> L{"more n in nums?"}
+  L -- no --> E(["return count"])
+  L -- yes --> A["sum += n"]
+  A --> Q{"map has sum - k?"}
+  Q -- yes --> C["count += map.get(sum - k) — every earlier prefix that closes a window"]
+  Q -- no --> W["map.set(sum, count of sum + 1)"]
+  C --> W
+  W --> L
+```
+
 ## Solution
 
 ```js

apps/docs/content/(01-linear-structures)/prefix-sum/index.mdx

@@ -0,0 +1,5 @@
+---
+title: Prefix Sum
+description: 'A running total is stored at each index, so the sum of any range is one subtraction.'
+hidden: true
+---

apps/docs/content/(01-linear-structures)/prefix-sum/meta.ts

@@ -0,0 +1,3 @@
+import { defineMeta } from "blume";
+
+export default defineMeta({ title: "Prefix Sum", order: 2, icon: "sigma", display: "group" });

apps/docs/content/(01-linear-structures)/sliding-window/121-best-time-to-buy-and-sell-stock.mdx

@@ -1,13 +1,16 @@
 ---
 title: '121. Best Time to Buy and Sell Stock'
 description: You are given an array prices where prices[i] is the price of a given stock on the i^th day
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Dynamic Programming", slug: "dynamic-programming" }
+video: "1pkOgXD63yU"
 sidebar:
   label: 'Best Time to Buy and Sell Stock'
   badge: 'Easy'
 ---
 
-<Badge variant="accent">Sliding Window</Badge>
-
 ### Example 1:
 - Input: `prices = [7,1,5,3,6,4]`
 - Output: `5`
@@ -23,6 +26,24 @@ sidebar:
 - `1 <= prices.length <= 10^5`
 - `0 <= prices[i] <= 10^4`
 
+## Approach
+
+::::warning
+The diagram traces the code below literally. That code does not run: `curr` and `ans` are never initialised, so the first `curr > left` test raises `NameError`, and `left` holds a price rather than an index, so `prices[left]` indexes by value.
+::::
+
+```mermaid
+flowchart TD
+  S(["maxProfit(prices)"]) --> I["left = min(prices)"]
+  I --> F{"more right in range(len(prices))?"}
+  F -- no --> E(["return ans"])
+  F -- yes --> W{"curr > left?"}
+  W -- yes --> P["curr -= prices[left]; left += 1"]
+  P --> W
+  W -- no --> M["ans = max(ans, curr)"]
+  M --> F
+```
+
 ## Solution
 
 ```py

apps/docs/content/(01-linear-structures)/sliding-window/3-longest-substring-without-repeating-characters.mdx

@@ -1,13 +1,17 @@
 ---
 title: '3. Longest Substring Without Repeating Characters'
 description: Given a string s, find the length of the longest substring without duplicate characters
+icon: dot
+topics:
+  - { name: "Hash Table", slug: "hash-table" }
+  - { name: "String", slug: "string" }
+  - { name: "Sliding Window", slug: "sliding-window" }
+video: "wiGpQwVHdE0"
 sidebar:
   label: 'Longest Substring Without Repeating Characters'
   badge: 'Medium'
 ---
 
-<Badge variant="accent">Sliding Window</Badge>
-
 ### Example 1:
 - Input: `s = "abcabcbb"`
 - Output: `3`
@@ -28,6 +32,21 @@ sidebar:
 - `0 <= s.length <= 10^5`
 - `s` consists of English letters, digits, symbols and spaces.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["lengthOfLongestSubstring(s)"]) --> I["left = 0, ans = 0, window = set()"]
+  I --> L{"more (right, c) in s?"}
+  L -- no --> E(["return ans"])
+  L -- yes --> W{"c already in window?"}
+  W -- yes --> P["window.remove(s[left]); left += 1 — shrink until c is free"]
+  P --> W
+  W -- no --> A["window.add(c)"]
+  A --> M["ans = max(ans, right - left + 1)"]
+  M --> L
+```
+
 ## Solution
 
 ```py

apps/docs/content/(01-linear-structures)/sliding-window/424-longest-repeating-character-replacement.mdx

@@ -1,13 +1,17 @@
 ---
 title: '424. Longest Repeating Character Replacement'
 description: You are given a string s and an integer k. You can choose any character of the string and change it to any other uppercase English character. You can perform this operation at most k times
+icon: dot
+topics:
+  - { name: "Hash Table", slug: "hash-table" }
+  - { name: "String", slug: "string" }
+  - { name: "Sliding Window", slug: "sliding-window" }
+video: "gqXU1UyA8pk"
 sidebar:
   label: 'Longest Repeating Character Replacement'
   badge: 'Medium'
 ---
 
-<Badge variant="accent">Sliding Window</Badge>
-
 ### Example 1:
 - Input: `s = "ABAB", k = 2`
 - Output: `4`
@@ -24,6 +28,21 @@ sidebar:
 - `s` consists of only uppercase English letters.
 - `0 <= k <= s.length`
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["characterReplacement(s, k)"]) --> I["count = {}, res = 0, l = 0, maxF = 0"]
+  I --> L{"more (r, c) in s?"}
+  L -- no --> E(["return res"])
+  L -- yes --> A["count[c] += 1; maxF = max(maxF, count[c])"]
+  A --> W{"(r - l + 1) - maxF > k? — too many chars to replace"}
+  W -- yes --> P["count[s[l]] -= 1; l += 1 — shrink from the left"]
+  P --> W
+  W -- no --> M["res = max(res, r - l + 1)"]
+  M --> L
+```
+
 ## Solution
 
 ```py

apps/docs/content/(01-linear-structures)/sliding-window/567-permutation-in-string.mdx

@@ -1,13 +1,18 @@
 ---
 title: '567. Permutation in String'
 description: Given two strings s1 and s2, return true if s2 contains a permutation of s1, or false otherwise
+icon: dot
+topics:
+  - { name: "Hash Table", slug: "hash-table" }
+  - { name: "Two Pointers", slug: "two-pointers" }
+  - { name: "String", slug: "string" }
+  - { name: "Sliding Window", slug: "sliding-window" }
+video: "UbyhOgBN834"
 sidebar:
   label: 'Permutation in String'
   badge: 'Medium'
 ---
 
-<Badge variant="accent">Sliding Window</Badge>
-
 ### Example 1:
 - Input: `s1 = "ab", s2 = "eidbaooo"`
 - Output: `true`
@@ -22,6 +27,24 @@ sidebar:
 - `1 <= s1.length, s2.length <= 10^4`
 - `s1` and `s2` consist of lowercase English letters.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["checkInclusion(s1, s2)"]) --> G{"k = len(s1) > len(s2)?"}
+  G -- yes --> X(["return False"])
+  G -- no --> I["need = Counter(s1), window = Counter()"]
+  I --> L{"more (right, c) in s2?"}
+  L -- no --> E(["return False"])
+  L -- yes --> A["window[c] += 1"]
+  A --> B{"right >= k? — window is now longer than k"}
+  B -- yes --> C["drop s2[right - k] from window, deleting the key at 0"]
+  B -- no --> Q
+  C --> Q{"window == need?"}
+  Q -- yes --> R(["return True"])
+  Q -- no --> L
+```
+
 ## Solution
 
 ```py

apps/docs/content/(01-linear-structures)/sliding-window/index.mdx

@@ -1,6 +1,7 @@
 ---
 title: Sliding Window
 description: 'Sliding window is a specialized two-pointer family where the pointers define a contiguous interval and you maintain information about that entire interval as it moves.'
+hidden: true
 ---
 
 :::warning
@@ -54,7 +55,7 @@ Without an invariant, shrinking the window becomes arbitrary. You no longer know
 The window size never changes. The main task is updating the window state efficiently when one element enters and one leaves.
 :::
 
-![Sliding Window Fixed Size](../../public/sliding-window-fixed-size.svg)
+![Sliding Window Fixed Size](../../../public/sliding-window-fixed-size.svg)
 
 ### 2. Flexible-size windows with a validity rule
 
@@ -62,7 +63,7 @@ The window size never changes. The main task is updating the window state effici
 Here the window expands until invalid, then shrinks until valid again.
 :::
 
-![Flexible-size windows](../../public/sliding-window-flexible.svg)
+![Flexible-size windows](../../../public/sliding-window-flexible.svg)
 
 
 ### 3. Frequency-tracking windows
@@ -71,7 +72,7 @@ Here the window expands until invalid, then shrinks until valid again.
 The difficulty comes from keeping the bookkeeping correct as characters enter and leave.
 :::
 
-![Frequency-tracking windows](../../public/sliding-window-frequency.svg)
+![Frequency-tracking windows](../../../public/sliding-window-frequency.svg)
 
 ## How Sliding Window Differs From Other Two-Pointer Families
 

apps/docs/content/(01-linear-structures)/sliding-window/meta.ts

@@ -0,0 +1,3 @@
+import { defineMeta } from "blume";
+
+export default defineMeta({ title: "Sliding Window", order: 4, icon: "app-window", display: "group" });

apps/docs/content/(01-linear-structures)/stack/150-evaluate-reverse-polish-notation.mdx

@@ -1,13 +1,17 @@
 ---
 title: '150. Evaluate Reverse Polish Notation'
 description: You are given an array of strings tokens that represents an arithmetic expression in a Reverse Polish Notation
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Math", slug: "math" }
+  - { name: "Stack", slug: "stack" }
+video: "iu0082c4HDE"
 sidebar:
   label: 'Evaluate Reverse Polish Notation'
   badge: 'Medium'
 ---
 
-<Badge variant="accent">Stack</Badge>
-
 ### Example 1:
 - Input: `tokens = ["2","1","+","3","*"]`
 - Output: `9`
@@ -28,6 +32,21 @@ sidebar:
 - `1 <= tokens.length <= 10^4`
 - `tokens[i]` is either an operator: "+", "-", "*", or "/", or an integer in the range [-200, 200].
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["evalRPN(tokens)"]) --> I["stack = [], operations = + - * /"]
+  I --> L{"more token c?"}
+  L -- no --> E(["return stack[0]"])
+  L -- yes --> Q{"c is an operator?"}
+  Q -- no --> N["stack.append(int(c))"]
+  N --> L
+  Q -- yes --> P["y = stack.pop(), x = stack.pop() — order matters"]
+  P --> C["stack.append(operations[c](x, y))"]
+  C --> L
+```
+
 ## Solution
 
 ```py

apps/docs/content/(01-linear-structures)/stack/155-min-stack.mdx

@@ -1,13 +1,16 @@
 ---
 title: '155. Min Stack'
 description: Design a stack that supports push, pop, top, and retrieving the minimum element in constant time
+icon: dot
+topics:
+  - { name: "Stack", slug: "stack" }
+  - { name: "Design", slug: "design" }
+video: "qkLl7nAwDPo"
 sidebar:
   label: 'Min Stack'
   badge: 'Medium'
 ---
 
-<Badge variant="accent">Stack</Badge>
-
 ::::warning
 You must implement a solution with O(1) time complexity for each function.
 ::::
@@ -23,6 +26,28 @@ You must implement a solution with O(1) time complexity for each function.
 - Methods pop, top and getMin operations will always be called on non-empty stacks.
 - At most 3 * 10^4 calls will be made to push, pop, top, and getMin.
 
+## Approach
+
+```mermaid
+flowchart TD
+  subgraph state["two parallel stacks — same depth, always"]
+    A["stack — the values"]
+    B["minStack — the minimum as of that depth"]
+  end
+  state --> P
+  subgraph P["push(value)"]
+    P1["stack.append(value)"] --> P2["minStack.append(min(value, minStack[-1]))"]
+  end
+  state --> O
+  subgraph O["pop()"]
+    O1["pop both stacks together"]
+  end
+  state --> R
+  subgraph R["top() / getMin() — O(1)"]
+    R1(["stack[-1] / minStack[-1]"])
+  end
+```
+
 ## Solution
 
 ```py

apps/docs/content/(01-linear-structures)/stack/20-valid-parentheses.mdx

@@ -1,13 +1,17 @@
 ---
 title: '20. Valid Parentheses'
 description: Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid
+icon: dot
+topics:
+  - { name: "String", slug: "string" }
+  - { name: "Stack", slug: "stack" }
+  - { name: "Bracket Sequences", slug: "bracket-sequences" }
+video: "WTzjTskDFMg"
 sidebar:
   label: 'Valid Parentheses'
   badge: 'Easy'
 ---
 
-<Badge variant="accent">Stack</Badge>
-
 ### Example 1:
 - Input: `s = "()"`
 - Output: `true`
@@ -33,6 +37,24 @@ sidebar:
 - `1 <= s.length <= 10^4`
 - `s` consists of parentheses only '()[]{}'.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["isValid(s)"]) --> I["stack = [], pairs = closer to opener"]
+  I --> L{"more char c?"}
+  L -- no --> Z{"stack empty?"}
+  Z -- yes --> T(["return True"])
+  Z -- no --> U(["return False — unclosed openers left"])
+  L -- yes --> Q{"c is a closer?"}
+  Q -- no --> A["stack.append(c) — it is an opener"]
+  A --> L
+  Q -- yes --> M{"stack non-empty and pairs[c] == stack[-1]?"}
+  M -- yes --> P["stack.pop() — matched"]
+  P --> L
+  M -- no --> F(["return False — mismatch"])
+```
+
 ## Solution
 
 ```py

apps/docs/content/(01-linear-structures)/stack/index.mdx

@@ -0,0 +1,5 @@
+---
+title: Stack
+description: 'Items are added and removed from one end, so the last item added is the first item removed.'
+hidden: true
+---

apps/docs/content/(01-linear-structures)/stack/meta.ts

@@ -0,0 +1,3 @@
+import { defineMeta } from "blume";
+
+export default defineMeta({ title: "Stack", order: 6, icon: "layers", display: "group" });

apps/docs/content/(01-linear-structures)/two-pointers/11-container-with-most-water.mdx

@@ -1,13 +1,17 @@
 ---
 title: '11. Container With Most Water'
 description: You are given an integer array height of length n. There are n vertical lines drawn such that the two endpoints of the i^th line are (i, 0) and (i, height[i])
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Two Pointers", slug: "two-pointers" }
+  - { name: "Greedy", slug: "greedy" }
+video: "UuiTKBwPgAo"
 sidebar:
   label: 'Container With Most Water'
   badge: 'Medium'
 ---
 
-<Badge variant="accent">Two Pointers</Badge>
-
 ::::warning
 Notice that you may not slant the container.
 ::::
@@ -27,6 +31,22 @@ Notice that you may not slant the container.
 - `2 <= n <= 10^5`
 - `0 <= height[i] <= 10^4`
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["maxArea(height)"]) --> I["res = 0, left = 0, right = len - 1"]
+  I --> W{"left < right?"}
+  W -- no --> E(["return res"])
+  W -- yes --> A["area = (right - left) * min(height[left], height[right])"]
+  A --> M["res = max(res, area)"]
+  M --> C{"height[left] < height[right]?"}
+  C -- yes --> L["left += 1 — drop the shorter wall"]
+  C -- no --> R["right -= 1 — drop the shorter wall"]
+  L --> W
+  R --> W
+```
+
 ## Solution
 
 ```py

apps/docs/content/(01-linear-structures)/two-pointers/125-valid-palindrome.mdx

@@ -1,13 +1,16 @@
 ---
 title: '125. Valid Palindrome'
 description: A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forward and backward. Alphanumeric characters include letters and numbers
+icon: dot
+topics:
+  - { name: "Two Pointers", slug: "two-pointers" }
+  - { name: "String", slug: "string" }
+video: "jJXJ16kPFWg"
 sidebar:
   label: 'Valid Palindrome'
   badge: 'Easy'
 ---
 
-<Badge variant="accent">Two Pointers</Badge>
-
 ### Example 1:
 - Input: `s = "A man, a plan, a canal: Panama"`
 - Output: `true`
@@ -28,6 +31,20 @@ sidebar:
 - `1 <= s.length <= 2 * 10^5`
 - `s` consists only of printable ASCII characters.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["isPalindrome(s)"]) --> N["normal = s stripped of non-alphanumerics, lowercased"]
+  N --> I["i = 0, j = normal.length - 1"]
+  I --> W{"i < j?"}
+  W -- no --> E(["return true — the pointers met in the middle"])
+  W -- yes --> Q{"normal[i] != normal[j]?"}
+  Q -- yes --> F(["return false"])
+  Q -- no --> A["i++; j-- — step both inward"]
+  A --> W
+```
+
 ## Solution
 
 ```js

apps/docs/content/(01-linear-structures)/two-pointers/15-3sum.mdx

@@ -1,13 +1,17 @@
 ---
 title: '15. 3Sum'
 description: Given an integer array nums, return all the triplets [nums[i], nums[j], nums[k]] such that i != j, i != k, and j != k, and nums[i] + nums[j] + nums[k] == 0
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Two Pointers", slug: "two-pointers" }
+  - { name: "Sorting", slug: "sorting" }
+video: "jzZsG8n2R9A"
 sidebar:
   label: '3Sum'
   badge: 'Medium'
 ---
 
-<Badge variant="accent">Two Pointers</Badge>
-
 ::::warning
 Notice that the solution set must not contain duplicate triplets.
 ::::
@@ -32,6 +36,28 @@ Notice that the solution set must not contain duplicate triplets.
 - `3 <= nums.length <= 3000`
 - `-10^5 <= nums[i] <= 10^5`
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["threeSum(nums)"]) --> O["nums.sort() — duplicates become adjacent"]
+  O --> F{"more i in 0..n-1?"}
+  F -- no --> E(["return result"])
+  F -- yes --> D{"nums[i] == nums[i-1]?"}
+  D -- yes --> F
+  D -- no --> P["left = i+1, right = n-1, target = -nums[i]"]
+  P --> W{"left < right?"}
+  W -- no --> F
+  W -- yes --> C["current = nums[left] + nums[right]"]
+  C --> Q{"current vs target"}
+  Q -- equal --> A["append triplet, skip equal neighbours, left += 1, right -= 1"]
+  A --> W
+  Q -- "current < target" --> L["left += 1 — need a bigger sum"]
+  L --> W
+  Q -- "current > target" --> R["right -= 1 — need a smaller sum"]
+  R --> W
+```
+
 ## Solution
 
 ```py

apps/docs/content/(01-linear-structures)/two-pointers/167-two-sum-ii-input-array-is-sorted.mdx

@@ -1,13 +1,17 @@
 ---
 title: '167. Two Sum II - Input Array Is Sorted'
 description: Given a 1-indexed array of integers numbers that is already sorted in non-decreasing order, find two numbers such that they add up to a specific target number. Let these two numbers be numbers[index1] and numbers[index2] where 1 <= index1 < index2 <= numbers.length
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Two Pointers", slug: "two-pointers" }
+  - { name: "Binary Search", slug: "binary-search" }
+video: "cQ1Oz4ckceM"
 sidebar:
   label: 'Two Sum II - Input Array Is Sorted'
   badge: 'Medium'
 ---
 
-<Badge variant="accent">Two Pointers</Badge>
-
 ::::warning
 Your solution must use only constant extra space.
 ::::
@@ -35,6 +39,22 @@ Your solution must use only constant extra space.
 - `-1000 <= target <= 1000`
 - The tests are generated such that there is exactly one solution.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["twoSum(numbers, target)"]) --> I["i = 0, j = len - 1"]
+  I --> W{"i < j?"}
+  W -- no --> E(["return []"])
+  W -- yes --> C["c = numbers[i] + numbers[j]"]
+  C --> Q{"c vs target"}
+  Q -- equal --> R(["return [i+1, j+1] — 1-indexed"])
+  Q -- "c < target" --> L["i += 1 — grow the sum"]
+  L --> W
+  Q -- "c > target" --> H["j -= 1 — shrink the sum"]
+  H --> W
+```
+
 ## Solution
 
 ```py

apps/docs/content/(01-linear-structures)/two-pointers/344-reverse-string.mdx

@@ -1,13 +1,16 @@
 ---
 title: '344. Reverse String'
 description: Write a function that reverses a string. The input string is given as an array of characters s
+icon: dot
+topics:
+  - { name: "Two Pointers", slug: "two-pointers" }
+  - { name: "String", slug: "string" }
+video: "_d0T_2Lk2qA"
 sidebar:
   label: 'Reverse String'
   badge: 'Easy'
 ---
 
-<Badge variant="accent">Two Pointers</Badge>
-
 :::warning
 You must do this by modifying the input array in-place with O(1) extra memory.
 :::
@@ -25,6 +28,18 @@ You must do this by modifying the input array in-place with O(1) extra memory.
 - `1 <= s.length <= 10^5`
 - `s[i]` is a printable ascii character.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["reverseString(s)"]) --> I["i = 0, j = s.length - 1"]
+  I --> W{"i < j?"}
+  W -- no --> E(["done — s was reversed in place, nothing returned"])
+  W -- yes --> A["swap s[i] and s[j]"]
+  A --> B["i++; j--"]
+  B --> W
+```
+
 ## Solution
 
 ```js

apps/docs/content/(01-linear-structures)/two-pointers/392-is-subsequence.mdx

@@ -1,13 +1,17 @@
 ---
 title: '392. Is Subsequence'
 description: Given two strings s and t, return true if s is a subsequence of t, or false otherwise
+icon: dot
+topics:
+  - { name: "Two Pointers", slug: "two-pointers" }
+  - { name: "String", slug: "string" }
+  - { name: "Dynamic Programming", slug: "dynamic-programming" }
+video: "99RVfqklbCE"
 sidebar:
   label: 'Is Subsequence'
   badge: 'Easy'
 ---
 
-<Badge variant="accent">Two Pointers</Badge>
-
 ::::warning
 Suppose there are lots of incoming s, say s1, s2, ..., sk where k >= 10^9, and you want to check one by one to see if t has its subsequence. In this scenario, how would you change your code?
 ::::
@@ -26,6 +30,22 @@ Suppose there are lots of incoming s, say s1, s2, ..., sk where k >= 10^9, and y
 - `0 <= t.length <= 10^4`
 - `s` and `t` consist only of lowercase English letters.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["isSubsequence(s, t)"]) --> G{"len(s) > len(t)?"}
+  G -- yes --> X(["return False"])
+  G -- no --> I["i = 0 into s, j = 0 into t"]
+  I --> W{"i < len(s) and j < len(t)?"}
+  W -- no --> E(["return i == len(s) — every char of s was matched"])
+  W -- yes --> Q{"s[i] == t[j]?"}
+  Q -- yes --> A["i += 1 — consume the match"]
+  Q -- no --> B["j += 1 — always advance t"]
+  A --> B
+  B --> W
+```
+
 ## Solution
 
 ```py

apps/docs/content/(01-linear-structures)/two-pointers/977-squares-of-a-sorted-array.mdx

@@ -1,13 +1,17 @@
 ---
 title: '977. Squares of a Sorted Array'
 description: Given an integer array nums sorted in non-decreasing order, return an array of the squares of each number sorted in non-decreasing order
+icon: dot
+topics:
+  - { name: "Array", slug: "array" }
+  - { name: "Two Pointers", slug: "two-pointers" }
+  - { name: "Sorting", slug: "sorting" }
+video: "FPCZsG_AkUg"
 sidebar:
   label: 'Squares of a Sorted Array'
   badge: 'Easy'
 ---
 
-<Badge variant="accent">Two Pointers</Badge>
-
 ::::warning
 Squaring each element and sorting the new array is very trivial, could you find an O(n) solution using a different approach?
 ::::
@@ -27,6 +31,21 @@ Squaring each element and sorting the new array is very trivial, could you find
 - `-10^4 <= nums[i] <= 10^4`
 - `nums` is sorted in non-decreasing order.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["sortedSquares(nums)"]) --> I["ans = Array(n), left = 0, right = n - 1"]
+  I --> L{"more i from n-1 down to 0?"}
+  L -- no --> E(["return ans"])
+  L -- yes --> C{"abs(nums[left]) < abs(nums[right])?"}
+  C -- yes --> R["square = nums[right]; right--"]
+  C -- no --> F["square = nums[left]; left++"]
+  R --> W["ans[i] = square * square — fill from the back, largest first"]
+  F --> W
+  W --> L
+```
+
 ## Solution
 
 ```js

apps/docs/content/(01-linear-structures)/two-pointers/index.mdx

@@ -0,0 +1,5 @@
+---
+title: Two Pointers
+description: 'Two indices move through the data from different positions and meet at the answer.'
+hidden: true
+---

apps/docs/content/(01-linear-structures)/two-pointers/meta.ts

@@ -0,0 +1,3 @@
+import { defineMeta } from "blume";
+
+export default defineMeta({ title: "Two Pointers", order: 3, icon: "arrow-left-right", display: "group" });

apps/docs/content/(02-nodal-grid)/hybrid-structures/146-lru-cache.mdx

@@ -0,0 +1,116 @@
+---
+title: '146. LRU Cache'
+description: Design a data structure that follows the constraints of a Least Recently Used (LRU) cache
+icon: dot
+topics:
+  - { name: "Hash Table", slug: "hash-table" }
+  - { name: "Linked List", slug: "linked-list" }
+  - { name: "Design", slug: "design" }
+  - { name: "Doubly-Linked List", slug: "doubly-linked-list" }
+video: "7ABFKPK2hD4"
+sidebar:
+  label: 'LRU Cache'
+  badge: 'Medium'
+---
+
+### Example 1:
+- Input: ``
+- Output: ``
+- Explanation: Input ["LRUCache", "put", "put", "get", "put", "get", "put", "get", "get", "get"] `[[2]`, [1, 1], [2, 2], `[1]`, [3, 3], `[2]`, [4, 4], `[1]`, `[3]`, [4]] Output [null, null, null, `1`, null, `-1`, null, `-1`, `3`, 4] Explanation LRUCache lRUCache = new LRUCache(2); lRUCache.put(1, `1`); // cache is {1=1} lRUCache.put(2, `2`); // cache is {1=1, 2=2} lRUCache.get(1);    // return `1` lRUCache.put(3, `3`); // LRU `key` was `2`, evicts `key 2`, cache is {1=1, 3=3} lRUCache.get(2);    // returns `-1` (not found) lRUCache.put(4, `4`); // LRU `key` was `1`, evicts `key 1`, cache is {4=4, 3=3} lRUCache.get(1);    // return `-1` (not found) lRUCache.get(3);    // return `3` lRUCache.get(4);    // return `4`
+
+### Constraints:
+
+- `1 <= capacity <= 3000`
+- `0 <= key <= 10^4`
+- `0 <= value <= 10^5`
+- At most 2 * 10^5 calls will be made to get and put.
+
+## Approach
+
+```mermaid
+flowchart TD
+  subgraph state["state — dict for O(1) lookup, doubly linked list for O(1) reorder"]
+    H["head — least recent"] --- N["... nodes ..."] --- T["tail — most recent"]
+  end
+  subgraph get["get(key)"]
+    G1{"key in cache?"} -- no --> G2(["return -1"])
+    G1 -- yes --> G3["_remove_node then _add_node — move it beside the tail"]
+    G3 --> G4(["return node.value"])
+  end
+  subgraph put["put(key, value)"]
+    P1{"key in cache?"} -- yes --> P2["update value, _remove_node then _add_node"]
+    P1 -- no --> P3["new Node, cache[key] = node, _add_node"]
+    P3 --> P4{"len(cache) > capacity?"}
+    P4 -- yes --> P5["evict head.next — the least recent — and del cache[lru.key]"]
+    P4 -- no --> P6(["done"])
+    P2 --> P6
+    P5 --> P6
+  end
+  state --> get
+  state --> put
+```
+
+## Solution
+
+```py
+class Node:
+    def __init__(self, key=0, value=0):
+        self.key = key
+        self.value = value
+        self.prev = None
+        self.next = None
+
+
+class LRUCache:
+    def __init__(self, capacity: int):
+        self.capacity = capacity
+        self.cache = {}
+        self.head = Node()
+        self.tail = Node()
+        self.head.next = self.tail  # pyright: ignore[reportAttributeAccessIssue]
+        self.tail.prev = self.head  # pyright: ignore[reportAttributeAccessIssue]
+
+    def _remove_node(self, node):
+        prev_node = node.prev
+        next_node = node.next
+        prev_node.next = next_node
+        next_node.prev = prev_node
+
+    def _add_node(self, node):
+        # Insert just before the tail (most recent at end)
+        node.next = self.tail
+        node.prev = self.tail.prev
+        self.tail.prev.next = node  # pyright: ignore[reportAttributeAccessIssue]
+        self.tail.prev = node
+
+    def get(self, key: int) -> int:
+        if key not in self.cache:
+            return -1
+
+        node = self.cache[key]
+        self._remove_node(node)
+        self._add_node(node)
+        return node.value
+
+    def put(self, key: int, value: int) -> None:
+        if key in self.cache:
+            node = self.cache[key]
+            node.value = value
+            self._remove_node(node)
+            self._add_node(node)
+        else:
+            new_node = Node(key, value)
+            self.cache[key] = new_node
+            self._add_node(new_node)
+
+            if len(self.cache) > self.capacity:
+                lru = self.head.next  # Oldest node is next to the head
+                self._remove_node(lru)
+                del self.cache[lru.key]  # pyright: ignore[reportAttributeAccessIssue]
+
+
+# Your LRUCache object will be instantiated and called as such:
+# obj = LRUCache(capacity)
+# param_1 = obj.get(key)
+# obj.put(key,value)
+```

apps/docs/content/(02-nodal-grid)/hybrid-structures/2-add-two-numbers.mdx

@@ -0,0 +1,75 @@
+---
+title: '2. Add Two Numbers'
+description: You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order, and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list
+icon: dot
+topics:
+  - { name: "Linked List", slug: "linked-list" }
+  - { name: "Math", slug: "math" }
+  - { name: "Recursion", slug: "recursion" }
+video: "wgFPrzTjm7s"
+sidebar:
+  label: 'Add Two Numbers'
+  badge: 'Medium'
+---
+
+### Example 1:
+- Input: `l1 = [2,4,3], l2 = [5,6,4]`
+- Output: `[7,0,8]`
+- Explanation: `342 + 465 = 807`.
+
+### Example 2:
+- Input: `l1 = [0], l2 = [0]`
+- Output: `[0]`
+
+### Example 3:
+- Input: `l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]`
+- Output: `[8,9,9,9,0,0,0,1]`
+
+### Constraints:
+
+- The number of nodes in each linked list is in the range [1, 100].
+- `0 <= Node.val <= 9`
+- It is guaranteed that the list represents a number that does not have leading zeros.
+
+## Approach
+
+```mermaid
+flowchart TD
+  S(["addTwoNumbers(l1, l2)"]) --> I["dummy = ListNode(), carry = 0, curr = dummy — dummy.next will be the head"]
+  I --> W{"l1 or l2 or carry?"}
+  W -- no --> E(["return dummy.next"])
+  W -- yes --> A["s = (l1.val if l1 else 0) + (l2.val if l2 else 0) + carry — a missing digit counts as 0"]
+  A --> D["carry, val = divmod(s, 10)"]
+  D --> N["curr.next = ListNode(val), curr = curr.next"]
+  N --> V["l1 = l1.next if l1 else None, l2 = l2.next if l2 else None"]
+  V --> W
+```
+
+## Solution
+
+```py
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def addTwoNumbers(
+        self, l1: Optional[ListNode], l2: Optional[ListNode]
+    ) -> Optional[ListNode]:
+
+        dummy = ListNode()
+        carry = 0
+        curr = dummy
+        while l1 or l2 or carry:
+            s = (l1.val if l1 else 0) + (l2.val if l2 else 0) + carry
+            carry, val = divmod(s, 10)
+
+            curr.next = ListNode(val)
+            curr = curr.next
+
+            l1 = l1.next if l1 else None
+            l2 = l2.next if l2 else None
+
+        return dummy.next
+```

apps/docs/content/(02-nodal-grid)/hybrid-structures/index.mdx

@@ -0,0 +1,5 @@
+---
+title: Hybrid Structures
+description: 'Two structures are combined, such as a hash map and a linked list, to get the best properties of each.'
+hidden: true
+---

apps/docs/content/(02-nodal-grid)/hybrid-structures/meta.ts

@@ -0,0 +1,3 @@
+import { defineMeta } from "blume";
+
+export default defineMeta({ title: "Hybrid Structures", order: 9, icon: "combine", display: "group" });

apps/docs/content/(02-nodal-grid)/linked-list/141-linked-list-cycle.mdx

@@ -1,13 +1,18 @@
 ---
 title: '141. Linked List Cycle'
 description: Given head, the head of a linked list, determine if the linked list has a cycle in it
+icon: dot
+topics:
+  - { name: "Hash Table", slug: "hash-table" }
+  - { name: "Linked List", slug: "linked-list" }
+  - { name: "Two Pointers", slug: "two-pointers" }
+  - { name: "Floyd's Cycle Finding Algorithm", slug: "floyds-cycle-finding-algorithm" }
+video: "gBTe7lFR3vc"
 sidebar:
   label: 'Linked List Cycle'
   badge: 'Easy'
 ---
 
-<Badge variant="accent">Linked List</Badge>
-
 ::::warning
 Can you solve it using O(1) (i.e. constant) memory?
 ::::
@@ -33,6 +38,20 @@ Can you solve it using O(1) (i.e. constant) memory?
 - `-10^5 <= Node.val <= 10^5`
 - pos is -1 or a valid index in the linked-list.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["hasCycle(head)"]) --> I["fast = slow = head"]
+  I --> W{"fast and fast.next?"}
+  W -- no --> E(["return False — ran off the end, no cycle"])
+  W -- yes --> A["fast = fast.next.next — two steps"]
+  A --> B["slow = slow.next — one step"]
+  B --> Q{"fast is slow?"}
+  Q -- yes --> R(["return True — the gap closed, so it loops"])
+  Q -- no --> W
+```
+
 ## Solution
 
 ```py

apps/docs/content/(02-nodal-grid)/linked-list/206-reverse-linked-list.mdx

@@ -1,13 +1,16 @@
 ---
 title: '206. Reverse Linked List'
 description: Given the head of a singly linked list, reverse the list, and return the reversed list
+icon: dot
+topics:
+  - { name: "Linked List", slug: "linked-list" }
+  - { name: "Recursion", slug: "recursion" }
+video: "G0_I-ZF0S38"
 sidebar:
   label: 'Reverse Linked List'
   badge: 'Easy'
 ---
 
-<Badge variant="accent">Linked List</Badge>
-
 ::::warning
 A linked list can be reversed either iteratively or recursively. Could you implement both?
 ::::
@@ -29,6 +32,19 @@ A linked list can be reversed either iteratively or recursively. Could you imple
 - The number of nodes in the list is the range [0, 5000].
 - `-5000 <= Node.val <= 5000`
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["reverseList(head)"]) --> I["prev = None, curr = head"]
+  I --> W{"curr?"}
+  W -- no --> E(["return prev — the old tail is the new head"])
+  W -- yes --> A["next_ = curr.next — save it before overwriting"]
+  A --> B["curr.next = prev — flip the link"]
+  B --> C["prev = curr; curr = next_ — step forward"]
+  C --> W
+```
+
 ## Solution
 
 ```py

apps/docs/content/(02-nodal-grid)/linked-list/21-merge-two-sorted-lists.mdx

@@ -1,13 +1,16 @@
 ---
 title: '21. Merge Two Sorted Lists'
 description: You are given the heads of two sorted linked lists list1 and list2
+icon: dot
+topics:
+  - { name: "Linked List", slug: "linked-list" }
+  - { name: "Recursion", slug: "recursion" }
+video: "XIdigk956u0"
 sidebar:
   label: 'Merge Two Sorted Lists'
   badge: 'Easy'
 ---
 
-<Badge variant="accent">Linked List</Badge>
-
 ### Example 1:
 - Input: `list1 = [1,2,4], list2 = [1,3,4]`
 - Output: `[1,1,2,3,4,4]`
@@ -26,6 +29,23 @@ sidebar:
 - `-100 <= Node.val <= 100`
 - Both list1 and list2 are sorted in non-decreasing order.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["mergeTwoLists(list1, list2)"]) --> G1{"list1 empty?"}
+  G1 -- yes --> X1(["return list2"])
+  G1 -- no --> G2{"list2 empty?"}
+  G2 -- yes --> X2(["return list1"])
+  G2 -- no --> H["head = the smaller first node; advance that list"]
+  H --> C["current = head"]
+  C --> W{"list1 and list2 both non-empty?"}
+  W -- yes --> P["current.next = the smaller node; advance that list; current = current.next"]
+  P --> W
+  W -- no --> T["current.next = list1 or list2 — append the leftover tail"]
+  T --> E(["return head"])
+```
+
 ## Solution
 
 ```py