feat(cli): add topic grouping with meta.ts generation in sync script

apps/cli/sync.ts

@@ -4,18 +4,25 @@
  *
  * - New problems get a full page (frontmatter, badge, 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
+ *   `<Badge>` line 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.
  *
+ * Two classifications, two homes. The sidebar group is the campaign TOPIC
+ * from the README table (`(tree-dfs)/`, ordered by topic number via a
+ * script-owned `meta.ts`); the page badge is the data-structure CATEGORY the
+ * file sits under in `work/1/<Difficulty>/<Category>/`. A problem outside the
+ * plan (warm-ups) has no topic, so it groups under its category instead.
+ *
  * 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`.
  */
-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";
 
 const ROOT = join(import.meta.dir, "..", "..");
 const WORK = join(ROOT, "work", "1");
@@ -158,24 +165,42 @@ function parseHeader(header: string): Header {
 
 // ── README topic map ─────────────────────────────────────────────
 
+/** 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;
+}
+
 const TOPIC_ALIASES: Record<string, string> = {
   "Hash-Based Lookup": "Hash Table",
 };
 
-async function readmeTopics(): Promise<Map<number, string>> {
+/** 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 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 t = line.match(/<strong>(\d+)\.\s*([^<]+)<\/strong>/);
+    if (t) topic = { order: Number(t[1]), name: TOPIC_ALIASES[t[2]!.trim()] ?? t[2]!.trim() };
     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;
 }
 
+/** `(group)` folder name: route-transparent in Blume, so only the sidebar sees it. */
+function groupFolder(topic: Topic): string {
+  return `(${topic.name.toLowerCase().replace(/[^a-z0-9]+/g, "-").replace(/^-|-$/g, "")})`;
+}
+
+/** Blume folder meta: exact topic label (the folder slug loses `/` and case) and curriculum order. */
+function groupMeta(topic: Topic): string {
+  const order = topic.order === undefined ? "" : `, order: ${topic.order}`;
+  return `import { defineMeta } from "blume";\n\nexport default defineMeta({ title: ${JSON.stringify(topic.name)}${order} });\n`;
+}
+
 // ── inline-code formatting heuristics ────────────────────────────
 
 /** Identifiers worth backticking in prose, harvested from the code. */
@@ -277,7 +302,11 @@ function warningText(h: Header): string {
   );
 }
 
-function renderPage(sol: Solution, topic: string): string {
+function badgeLine(sol: Solution): string {
+  return `<Badge variant="accent">${sol.category}</Badge>`;
+}
+
+function renderPage(sol: Solution): string {
   const h = sol.header;
   const ids = identifiers(sol);
   const description = h.statement[0]?.replace(/\.\s*$/, "") ?? "";
@@ -292,7 +321,7 @@ function renderPage(sol: Solution, topic: string): string {
     `  badge: '${h.difficulty}'`,
     "---",
     "",
-    `<Badge variant="accent">${topic}</Badge>`,
+    badgeLine(sol),
     "",
   );
 
@@ -387,12 +416,18 @@ 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>(); // folder -> topic, for meta.ts
+const vacated = new Set<string>(); // folders a page moved out of; removed below if empty
 
 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(" ", "-")})`;
+  // (topic) group folder + leetcode-number prefix: numeric sidebar order, both stripped from the URL.
+  // An unplanned problem's category may share a folder with a numbered topic
+  // (`Hash Table` warm-ups under topic 1); the numbered one owns the meta.
+  const topic = topics.get(sol.num) ?? { name: sol.category };
+  const group = groupFolder(topic);
+  if (groups.get(group)?.order === undefined) groups.set(group, topic);
   const name = `${group}/${sol.num}-${sol.slug}.mdx`;
   const existing = pages.get(sol.num);
   await mkdir(join(DOCS, group), { recursive: true });
@@ -406,10 +441,11 @@ for (const sol of ordered) {
     }
     const tail = page.slice(solutionEnd(page, at));
     const body = page.slice(0, at) + solutionSection(sol) + (tail ? `\n${tail}` : "");
-    const next = ensureLabel(body, sol.header);
+    const next = ensureLabel(body, sol.header).replace(/^<Badge variant="accent">.*<\/Badge>$/m, badgeLine(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) {
@@ -418,12 +454,30 @@ for (const sol of ordered) {
     }
     report.push([workRef, name, actions.join(" + ") || "skipped (in sync)"]);
   } else {
-    const topic = topics.get(sol.num) ?? sol.category;
-    await Bun.write(join(DOCS, name), renderPage(sol, topic));
+    await Bun.write(join(DOCS, name), renderPage(sol));
     report.push([workRef, name, "created"]);
   }
 }
 
+// Script-owned folder meta: one per live group, rewritten only when it differs.
+for (const [group, topic] of groups) {
+  const path = join(DOCS, group, "meta.ts");
+  const meta = groupMeta(topic);
+  if ((await Bun.file(path).exists()) && (await Bun.file(path).text()) === meta) continue;
+  await Bun.write(path, meta);
+  report.push([`topic ${topic.order ?? "-"}`, `${group}/meta.ts`, "written"]);
+}
+
+// A group every page left behind is dead: drop its meta and the folder itself.
+for (const dir of vacated) {
+  if (groups.has(dir)) continue;
+  const left = await readdir(join(DOCS, dir));
+  if (left.some((f) => f !== "meta.ts")) continue;
+  if (left.length) await unlink(join(DOCS, dir, "meta.ts"));
+  await rmdir(join(DOCS, dir));
+  report.push(["", dir, "removed (empty)"]);
+}
+
 const w0 = Math.max(...report.map((r) => r[0].length), 9);
 const w1 = Math.max(...report.map((r) => r[1].length), 9);
 console.log(`${"work file".padEnd(w0)}  ${"docs page".padEnd(w1)}  status`);