feat(cli): add company frequency frontmatter to docs sync

apps/cli/sync.ts

@@ -27,6 +27,15 @@
  *   (never on a sync with nothing new); offline, or with no `gh` auth, the
  *   page is written without it and the next sync retries. Delete the key to
  *   refetch it.
+ * - Every page carries the companies that asked it in the last six months as
+ *   frontmatter `companies:` (`{ name, period, frequency }`, the most recent
+ *   window each company falls in and its frequency there, most recent first;
+ *   `apps/docs/companies.ts`), read from the local DuckDB
+ *   company-frequency database (`COMPANY_DB`, built by its own `mise run
+ *   lc:build`) with the `duckdb` CLI. Unlike the keys above it is rewritten
+ *   every run, since recency ages and a rebuilt database should show; a
+ *   problem no company asked lately carries no key. Where the database or the
+ *   CLI is missing (CI), the step is skipped and pages keep the key as is.
  * - Every tag a page carries that no campaign topic teaches (not a key of
  *   `apps/docs/topic-landings.ts`) belongs in the Appendix glossary,
  *   `apps/docs/appendix.ts`, which is hand-written: sync only checks it,
@@ -63,10 +72,13 @@
  * `apps/docs/redirects.ts`, which `blume.config.ts` imports — Blume takes exact
  * root-relative paths and prepends the deployment base itself.
  */
+import { existsSync } from "node:fs";
 import { mkdir, readdir, rename, rmdir, unlink } from "node:fs/promises";
+import { homedir } from "node:os";
 import { basename, dirname, join } from "node:path";
 
 import { APPENDIX } from "../docs/appendix.ts";
+import { RECENCY, type Company } from "../docs/companies.ts";
 import { TOPIC_LANDINGS } from "../docs/topic-landings.ts";
 import { github } from "./github.ts";
 
@@ -506,6 +518,62 @@ async function issueUrl(sol: Solution): Promise<string | undefined> {
   return url;
 }
 
+// ── company frequency ────────────────────────────────────────────
+
+// The windows and the key's shape are `apps/docs/companies.ts`, shared with
+// the schema and the readers; `More Than Six Months` and `All` are not recent.
+const COMPANY_DB = join(
+  process.env.XDG_DATA_HOME ?? join(homedir(), ".local", "share"),
+  "duckdb",
+  "data",
+  "leetcode-company-frequency.db",
+);
+
+/**
+ * LC number → the companies that asked it in the last six months, each at the
+ * most recent window it appears in (the windows nest), ordered most recent
+ * first, then by that window's frequency. Undefined when this machine has no
+ * database or no `duckdb` CLI — the step is skipped — or the query fails
+ * (warned). One query for every solved problem.
+ */
+function recentCompanies(nums: number[]): Map<number, Company[]> | undefined {
+  if (!existsSync(COMPANY_DB) || !Bun.which("duckdb")) return undefined;
+  const order = `list_position([${RECENCY.map((p) => `'${p}'`).join(", ")}], period)`;
+  const sql = `SELECT question_id, company, period, frequency FROM company_frequency
+    WHERE question_id IN (${nums.join(", ")}) AND ${order} IS NOT NULL
+    QUALIFY row_number() OVER (PARTITION BY question_id, company ORDER BY ${order}) = 1
+    ORDER BY question_id, ${order}, frequency DESC, company`;
+  const proc = Bun.spawnSync(["duckdb", "-readonly", "-json", COMPANY_DB, "-c", sql]);
+  if (!proc.success) {
+    console.warn(`no companies: duckdb -> ${proc.stderr.toString().trim()}`);
+    return undefined;
+  }
+  const out = proc.stdout.toString().trim();
+  const rows: unknown = out ? JSON.parse(out) : [];
+  const companies = new Map<number, Company[]>(nums.map((n) => [n, []]));
+  for (const row of Array.isArray(rows) ? rows : []) {
+    if (!row || typeof row !== "object") continue;
+    if (!("question_id" in row) || typeof row.question_id !== "number") continue;
+    if (!("company" in row) || typeof row.company !== "string") continue;
+    if (!("period" in row) || !("frequency" in row) || typeof row.frequency !== "number") continue;
+    const period = RECENCY.find((p) => p === row.period);
+    if (period)
+      companies.get(row.question_id)?.push({ name: row.company, period, frequency: row.frequency });
+  }
+  return companies;
+}
+
+/** The frontmatter `companies:` block, one flow mapping per company (JSON strings are valid YAML). */
+function companiesYaml(list: Company[]): string {
+  return [
+    "companies:",
+    ...list.map(
+      (c) =>
+        `  - { name: ${JSON.stringify(c.name)}, period: ${JSON.stringify(c.period)}, frequency: ${c.frequency} }`,
+    ),
+  ].join("\n");
+}
+
 // ── inline-code formatting heuristics ────────────────────────────
 
 /** Identifiers worth backticking in prose, harvested from the code. */
@@ -624,6 +692,7 @@ function renderPage(
   sol: Solution,
   tags: TopicTag[] | undefined,
   issue: string | undefined,
+  companies: Company[] | undefined,
 ): string {
   const h = sol.header;
   const ids = identifiers(sol);
@@ -639,6 +708,7 @@ function renderPage(
     `icon: ${PAGE_ICON}`,
     ...(tags ? [topicsYaml(tags)] : []),
     ...(issue ? [`issue: ${JSON.stringify(issue)}`] : []),
+    ...(companies?.length ? [companiesYaml(companies)] : []),
     "sidebar:",
     `  label: '${h.title.replaceAll("'", "''")}'`,
     `  badge: '${h.difficulty}'`,
@@ -704,6 +774,7 @@ for await (const rel of new Bun.Glob("**/*.{js,py}").scan(WORK)) {
 }
 
 const topics = await readmeTopics();
+const companies = recentCompanies([...solutions.keys()]);
 // 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/`.
@@ -753,6 +824,23 @@ async function ensureIssue(page: string, sol: Solution): Promise<string> {
   );
 }
 
+/**
+ * Replace the frontmatter's `companies:` with this run's list, inserted before
+ * `sidebar:` (dropped when no company asked lately). Without the database the
+ * page is returned untouched, so an environment lacking it never strips the key.
+ */
+function ensureCompanies(page: string, sol: Solution): string {
+  if (!companies) return page;
+  const fm = page.match(/^---\n[\s\S]*?\n---/);
+  if (!fm) return page;
+  const list = companies.get(sol.num) ?? [];
+  const without = fm[0].replace(/^companies:.*\n(?: {2}- .*\n)*/m, "");
+  const next = list.length
+    ? without.replace(/^sidebar:$/m, `${companiesYaml(list)}\nsidebar:`)
+    : without;
+  return next + 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
@@ -815,9 +903,12 @@ for (const sol of ordered) {
     const tail = page.slice(solutionEnd(page, at));
     const body =
       page.slice(0, at) + solutionSection(sol) + (tail ? `\n${tail}` : "");
-    const next = await ensureIssue(
+    const next = ensureCompanies(
+      await ensureIssue(
         await ensureTopics(ensureIcon(ensureLabel(body, sol.header)), sol),
         sol,
+      ),
+      sol,
     );
     const actions: string[] = [];
     if (existing !== name) {
@@ -836,6 +927,7 @@ for (const sol of ordered) {
       sol,
       await fetchTopicTags(sol),
       await issueUrl(sol),
+      companies?.get(sol.num),
     );
     await Bun.write(join(DOCS, name), page);
     report.push([workRef, name, "created"]);