fix(prd): stop PRD titles corrupting the README index (#31)

regenerateIndex() passed the new index block to String.replace() as a
replacement string, so a PRD title containing a special pattern ($&, $`,
$', $$) was interpreted instead of inserted literally — splicing the old
index back into itself and corrupting prd/README.md.

Use a function replacement (() => block) so the block is written verbatim
regardless of title content. Adds a regression test.

Co-authored-by: clawedassistant26 <307253840+clawedassistant26@users.noreply.github.com>

Author: clawedassistant26

src/prd.mjs

@@ -217,9 +217,13 @@ export function regenerateIndex(root = process.cwd()) {
     ? ["| # | Title | Status |", "|---|---|---|",
        ...prds.map((p) => `| [${p.id}](${p.file}) | ${p.title} | ${p.status} |`)].join("\n")
     : "_No PRDs yet._";
+  // Use a function replacement so `$`-sequences in a PRD title (e.g. `$&`, `$1`,
+  // `$\`` ) are inserted verbatim instead of being read as String.replace special
+  // patterns, which would otherwise splice the match back in and corrupt the index.
+  const block = `${INDEX_START}\n${rows}\n${INDEX_END}`;
   const next = body.replace(
     new RegExp(`${INDEX_START}[\\s\\S]*${INDEX_END}`),
-    `${INDEX_START}\n${rows}\n${INDEX_END}`,
+    () => block,
   );
   if (next === body) return false;
   fs.writeFileSync(readme, next);

test/prd.test.mjs

@@ -1,7 +1,10 @@
 import assert from "node:assert/strict";
 import test from "node:test";
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
 
-import { renderPrd } from "../src/prd.mjs";
+import { createPrd, renderPrd } from "../src/prd.mjs";
 
 test("renderPrd quotes titles so YAML metacharacters stay valid", () => {
   const body = renderPrd({
@@ -13,3 +16,26 @@ test("renderPrd quotes titles so YAML metacharacters stay valid", () => {
 
   assert.match(body, /^title: "Ship CLI: handle \\"quoted\\" flags"$/m);
 });
+
+
+test("regenerateIndex keeps the README intact when a title holds a String.replace pattern", () => {
+  // `$&`, `$\``, `$'`, `$$` are special in a String.replace *replacement string*.
+  // A PRD title carrying one must not splice the old index block back into itself.
+  const root = fs.mkdtempSync(path.join(os.tmpdir(), "moshcode-prd-"));
+  try {
+    createPrd("Add $& live support", root);
+    createPrd("Improve docs", root);
+
+    const readme = fs.readFileSync(path.join(root, "prd", "README.md"), "utf8");
+    const starts = (readme.match(/PRD-INDEX:START/g) || []).length;
+    const ends = (readme.match(/PRD-INDEX:END/g) || []).length;
+
+    assert.equal(starts, 1, "index start marker must appear exactly once");
+    assert.equal(ends, 1, "index end marker must appear exactly once");
+    // The literal title text survives; it is not expanded into the match.
+    assert.match(readme, /\$& live support/);
+    assert.match(readme, /Improve docs/);
+  } finally {
+    fs.rmSync(root, { recursive: true, force: true });
+  }
+});