fix(catalog): explicit section ownership, no body-sniffing heuristic

carriedSectionsFrom() decided whether a ## Usage section was generated by matching
its first line against a list of historical opener phrases — so a hand-written
Usage section that happened to open that way was classified as generated and
silently deleted on regeneration. Ownership is now purely set membership: a
section is generated iff its heading is one the template emits, and ambiguous
'usage' is no longer in that set (the template never emits it), so any ## Usage is
carried. Exported carriedSectionsFrom behind an entrypoint guard and added two
executable preservation fixtures. Flagged by Magi (#5).

packages/core/src/registry/catalogGeneratorInstructions.test.ts

@@ -1,7 +1,9 @@
-import { readdirSync, readFileSync } from "node:fs";
+import { mkdtempSync, readdirSync, readFileSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
 import { dirname, join, resolve } from "node:path";
 import { fileURLToPath } from "node:url";
-import { describe, expect, it } from "vitest";
+import { afterAll, describe, expect, it } from "vitest";
+import { carriedSectionsFrom } from "../../../../scripts/generate-catalog-pages.ts";
 
 const here = dirname(fileURLToPath(import.meta.url));
 const repoRoot = resolve(here, "../../../..");
@@ -39,3 +41,77 @@ describe("catalog pages keep the required reader continuation", () => {
     expect(lastHeading).toBe("## Related topics");
   });
 });
+
+// The carry-forward path is the subtler half: a regeneration must preserve every
+// hand-written section, including one whose heading (## Usage) the generator once
+// emitted and whose first line looks like generated prose, and one appended below
+// the generated footer marker.
+describe("carriedSectionsFrom preserves hand-written sections", () => {
+  const dir = mkdtempSync(join(tmpdir(), "hf-catalog-carry-"));
+  afterAll(() => rmSync(dir, { recursive: true, force: true }));
+
+  const write = (name: string, body: string) => {
+    const p = join(dir, name);
+    writeFileSync(p, body, "utf-8");
+    return p;
+  };
+
+  it("keeps a custom Usage section that opens like generated prose", () => {
+    const page = write(
+      "usage.mdx",
+      [
+        "## Install",
+        "",
+        "```bash Terminal",
+        "npx hyperframes add sample",
+        "```",
+        "",
+        "## Usage",
+        "",
+        // deliberately opens with a phrase an old generated Usage used
+        "After installing, add the block — but here is our own hand-written guidance the author cares about.",
+        "",
+        "{/* hf:generated-footer */}",
+        "",
+        "Tagged `sample`.",
+        "",
+      ].join("\n"),
+    );
+    const carried = carriedSectionsFrom(page);
+    const joined = carried.sections.join("\n");
+    expect(joined).toContain("## Usage");
+    expect(joined).toContain("hand-written guidance the author cares about");
+    expect(carried.hasCustomUsage).toBe(true);
+    // The generated Install section is owned by the template and not carried.
+    expect(joined).not.toContain("## Install");
+  });
+
+  it("keeps a hand-written section appended below the generated footer", () => {
+    const page = write(
+      "below-footer.mdx",
+      [
+        "## Install",
+        "",
+        "text",
+        "",
+        "{/* hf:generated-footer */}",
+        "",
+        "Tagged `sample`.",
+        "",
+        "## Related topics",
+        "",
+        "- [Browse the complete Catalog](/catalog)",
+        "",
+        "## Field notes",
+        "",
+        "A section a human added after the generated tail.",
+        "",
+      ].join("\n"),
+    );
+    const joined = carriedSectionsFrom(page).sections.join("\n");
+    expect(joined).toContain("## Field notes");
+    expect(joined).toContain("A section a human added after the generated tail.");
+    // The generator's own Related topics is not carried (it re-emits it).
+    expect(joined).not.toContain("## Related topics");
+  });
+});

scripts/generate-catalog-pages.ts

@@ -15,7 +15,7 @@
 
 import { readFileSync, existsSync, mkdirSync, writeFileSync, rmSync } from "node:fs";
 import { join, resolve, dirname } from "node:path";
-import { fileURLToPath } from "node:url";
+import { fileURLToPath, pathToFileURL } from "node:url";
 // Import from source — bun workspace linking doesn't resolve for scripts outside packages/.
 import {
   type FileTarget,
@@ -118,10 +118,12 @@ const GENERATED_HEADINGS = new Set([
   "ask an agent for it",
   "make the texture move",
   "every texture",
-  // headings earlier revisions emitted — dropped on purpose, never carried
+  // headings earlier revisions emitted — dropped on purpose, never carried.
+  // `usage` is deliberately NOT listed: the current template never emits it, and
+  // it is a heading a human might reasonably write, so ownership stays explicit
+  // (anything not in this set is hand-written) rather than sniffing the body.
   "details",
   "files",
-  "usage",
   "source prompt",
   "agent usage",
   "animated texture",
@@ -130,19 +132,6 @@ const GENERATED_HEADINGS = new Set([
   "related topics",
 ]);
 
-/**
- * Openers of every "## Usage" body this generator has written. A Usage section
- * that starts with none of them was rewritten by hand, so it is kept and the
- * generated usage prose steps aside for it.
- */
-const GENERATED_USAGE_OPENERS = [
-  /^After installing, add the block/,
-  /^Open `[^`]+` and paste its contents/,
-  /^Open `[^`]+` and copy what is inside/,
-  /^After `npx hyperframes add/,
-  /^It runs for /,
-];
-
 /**
  * Marks the start of the generated provenance footer (tags, credit, prompt).
  * That footer carries no heading of its own, so without this marker the section
@@ -170,8 +159,10 @@ const RELATED_TOPICS: readonly string[] = [
  * Pull the hand-written `## sections` out of an already-generated page.
  * Returns the raw lines, heading included, in their original order.
  */
+// Exported for the preservation fixture in
+// packages/core/src/registry/catalogGeneratorInstructions.test.ts.
 // fallow-ignore-next-line complexity
-function carriedSectionsFrom(pagePath: string): CarriedContent {
+export function carriedSectionsFrom(pagePath: string): CarriedContent {
   const empty: CarriedContent = { sections: [], hasCustomUsage: false };
   if (!existsSync(pagePath)) return empty;
   let text: string;
@@ -192,12 +183,12 @@ function carriedSectionsFrom(pagePath: string): CarriedContent {
     while (buffer.length && buffer[0]!.trim() === "") buffer.shift();
     while (buffer.length && buffer.at(-1)!.trim() === "") buffer.pop();
 
+    // Ownership is explicit: a section is generated iff its heading is one the
+    // template emits (GENERATED_HEADINGS). Everything else is hand-written and
+    // carried verbatim — no content heuristic that could misread custom prose as
+    // generated and silently delete it on the next regeneration.
     const key = heading.toLowerCase();
-    const handWritten =
+    if (!GENERATED_HEADINGS.has(key) && buffer.length) {
-      !GENERATED_HEADINGS.has(key) ||
-      (key === "usage" && !GENERATED_USAGE_OPENERS.some((re) => re.test(buffer[0] ?? "")));
-
-    if (handWritten && buffer.length) {
       if (key === "usage") hasCustomUsage = true;
       sections.push(`## ${heading}`, "", ...buffer, "");
     }
@@ -844,4 +835,7 @@ function main(): void {
   console.log("\nDone.");
 }
 
+// Only regenerate when run directly, so the module can be imported by tests.
+if (import.meta.url === pathToFileURL(process.argv[1] ?? "").href) {
   main();
+}