diff --git a/.changeset/README.md b/.changeset/README.md
new file mode 100644
index 000000000..23e550926
--- /dev/null
+++ b/.changeset/README.md
@@ -0,0 +1,44 @@
+# Changeset Fragments
+
+This directory holds **per-PR CHANGELOG fragments**. Every PR with user-facing changes drops one (or more) `<random-name>.md` files here describing its CHANGELOG entry. Fragments are consolidated into the top-level `CHANGELOG.md` at release time.
+
+## Why
+
+Two PRs that both edit the `### Fixed` block of `CHANGELOG.md` always conflict on merge — git can't pick a serialization order without human input. Two PRs that each add a fresh `.changeset/<unique-name>.md` never conflict because they don't share lines.
+
+See [#2975](https://github.com/gsd-build/get-shit-done/issues/2975) for the full rationale.
+
+## Adding a fragment
+
+```bash
+node scripts/changeset/new.cjs \
+  --type Fixed \
+  --pr 1234 \
+  --body "fix the thing — explain the user-visible change in one sentence"
+```
+
+This writes `.changeset/<adjective>-<noun>-<noun>.md` with frontmatter and a body. Three random words → concurrent PRs don't collide.
+
+## Format
+
+```md
+---
+type: Fixed
+pr: 1234
+---
+**`/gsd-foo` no longer drops trailing slashes** — explain the user-visible change.
+```
+
+Allowed `type:` values follow [Keep a Changelog](https://keepachangelog.com/): `Added`, `Changed`, `Deprecated`, `Removed`, `Fixed`, `Security`.
+
+## Opting out
+
+PRs that legitimately have no user-facing impact can add the `no-changelog` label. CI honors it. When unsure, add the fragment.
+
+## At release time
+
+```bash
+node scripts/changeset/cli.cjs render --version vX.Y.Z --date YYYY-MM-DD
+```
+
+Reads every fragment, groups bullets by `type:`, replaces `## [Unreleased]` with a new `## [vX.Y.Z] - YYYY-MM-DD` block, opens a fresh `## [Unreleased]` above, deletes consumed fragments. Idempotent.
diff --git a/.changeset/eager-hawks-rally.md b/.changeset/eager-hawks-rally.md
new file mode 100644
index 000000000..589c8cb63
--- /dev/null
+++ b/.changeset/eager-hawks-rally.md
@@ -0,0 +1,5 @@
+---
+type: Added
+pr: 2975
+---
+**Changeset-fragment workflow** — eliminates CHANGELOG.md merge conflicts. Each PR drops `.changeset/<random-name>.md` with frontmatter (`type:`, `pr:`) plus a markdown body; the release-time `npm run changelog:render` consolidates fragments into `CHANGELOG.md` and deletes them. CI lint (`npm run lint:changeset`) requires a fragment on any PR touching user-facing files (`bin/`, `get-shit-done/`, `agents/`, `commands/`, `hooks/`, `sdk/src/`); contributors can opt out via the `no-changelog` label for purely internal changes. See [.changeset/README.md](.changeset/README.md) and CONTRIBUTING.md for the workflow.
diff --git a/.github/workflows/changeset-required.yml b/.github/workflows/changeset-required.yml
new file mode 100644
index 000000000..5baacee97
--- /dev/null
+++ b/.github/workflows/changeset-required.yml
@@ -0,0 +1,24 @@
+name: Changeset Required
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened, labeled, unlabeled]
+
+permissions:
+  contents: read
+  pull-requests: read
+
+jobs:
+  changeset-lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '24'
+      - name: Run changeset lint
+        env:
+          GITHUB_BASE_REF: ${{ github.base_ref }}
+        run: node scripts/changeset/lint.cjs
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 9502633da..862221517 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -91,6 +91,23 @@ PRs that arrive without a properly-labeled linked issue are closed automatically
 - **CI must pass** — all matrix jobs (Ubuntu × Node 22, 24; macOS × Node 24) must be green
 - **Scope matches the approved issue** — if your PR does more than what the issue describes, the extra changes will be asked to be removed or moved to a new issue
 
+## CHANGELOG Entries — Drop a Fragment
+
+**Do not edit `CHANGELOG.md` directly.** Two PRs that both append to a `### Fixed` block always conflict on merge — git can't pick a serialization order without a human. Instead, every PR with user-facing changes drops a fragment file in `.changeset/`.
+
+```bash
+npm run changeset -- --type Fixed --pr <YOUR_PR_NUMBER> \
+  --body "**\`/gsd-foo\` no longer drops trailing slashes** — explain the user-visible change."
+```
+
+This writes `.changeset/<adjective>-<noun>-<noun>.md`. Three random words → concurrent PRs never collide. Allowed `type:` values follow [Keep a Changelog](https://keepachangelog.com/): `Added`, `Changed`, `Deprecated`, `Removed`, `Fixed`, `Security`.
+
+Fragments are consolidated into `CHANGELOG.md` at release time by the release workflow. See [`.changeset/README.md`](.changeset/README.md) for the format spec and [#2975](https://github.com/gsd-build/get-shit-done/issues/2975) for the rationale.
+
+**CI enforcement:** the `Changeset Required` workflow (`scripts/changeset/lint.cjs`) fails any PR that touches `bin/`, `get-shit-done/`, `agents/`, `commands/`, `hooks/`, or `sdk/src/` without a `.changeset/*.md` fragment.
+
+**Opt-out:** PRs with no user-facing impact (test refactors, lint config changes, CI tweaks, formatting-only changes) can add the `no-changelog` label. The lint honors it. When unsure whether a change is user-facing, **add the fragment**.
+
 ## Testing Standards
 
 All tests use Node.js built-in test runner (`node:test`) and assertion library (`node:assert`). **Do not use Jest, Mocha, Chai, or any external test framework.**
diff --git a/package.json b/package.json
index 4d3156ab9..edd7209b7 100644
--- a/package.json
+++ b/package.json
@@ -62,6 +62,9 @@
     "pretest:coverage": "npm run build:sdk",
     "lint:descriptions": "node scripts/lint-descriptions.cjs",
     "lint:tests": "node scripts/lint-no-source-grep.cjs",
+    "lint:changeset": "node scripts/changeset/lint.cjs",
+    "changeset": "node scripts/changeset/new.cjs",
+    "changelog:render": "node scripts/changeset/cli.cjs render",
     "test": "node scripts/run-tests.cjs",
     "test:coverage": "c8 --check-coverage --lines 70 --reporter text --include 'get-shit-done/bin/lib/*.cjs' --exclude 'tests/**' --all node scripts/run-tests.cjs"
   }
diff --git a/scripts/changeset/cli.cjs b/scripts/changeset/cli.cjs
new file mode 100755
index 000000000..0d136a3a7
--- /dev/null
+++ b/scripts/changeset/cli.cjs
@@ -0,0 +1,191 @@
+#!/usr/bin/env node
+'use strict';
+
+/**
+ * CLI wrapper for the changeset-fragment workflow (#2975).
+ *
+ * Subcommands:
+ *   render --repo <dir> --version V --date D [--json]   Fold .changeset/*.md
+ *                                                       into CHANGELOG.md;
+ *                                                       delete consumed fragments.
+ *
+ * `--json` emits a structured report on stdout — the only contract tests
+ * assert against. Per CONTRIBUTING.md "Prohibited: Raw Text Matching on
+ * Test Outputs", the human formatter is operator-only.
+ */
+
+const fs = require('node:fs');
+const path = require('node:path');
+
+const { parseFragment, FRAGMENT_ERROR } = require('./parse.cjs');
+const { renderChangelog } = require('./render.cjs');
+const { serializeChangelog } = require('./serialize.cjs');
+
+function parseArgs(argv) {
+  const opts = { cmd: null, repo: process.cwd(), version: null, date: null, json: false };
+  if (argv.length === 0) return { ok: true, opts };
+  opts.cmd = argv[0];
+
+  // Pull a value for a value-taking flag, validating that the next token
+  // exists and is not itself another flag (which is the silently-misparsed
+  // case CR called out: e.g. `--repo --json` would consume `--json` as the
+  // repo path).
+  const requireValue = (flag, i) => {
+    const v = argv[i + 1];
+    if (v === undefined || v.startsWith('--')) {
+      return { ok: false, error: `missing value for ${flag}` };
+    }
+    return { ok: true, value: v };
+  };
+
+  for (let i = 1; i < argv.length; i++) {
+    const a = argv[i];
+    if (a === '--json') { opts.json = true; continue; }
+    if (a === '--repo' || a === '--version' || a === '--date') {
+      const r = requireValue(a, i);
+      if (!r.ok) return { ok: false, error: r.error };
+      if (a === '--repo') opts.repo = r.value;
+      else if (a === '--version') opts.version = r.value;
+      else if (a === '--date') opts.date = r.value;
+      i++;
+      continue;
+    }
+    return { ok: false, error: `unknown argument: ${a}` };
+  }
+  return { ok: true, opts };
+}
+
+function listFragmentFiles(changesetDir) {
+  if (!fs.existsSync(changesetDir)) return [];
+  return fs.readdirSync(changesetDir)
+    .filter((f) => f.endsWith('.md') && f !== 'README.md')
+    .map((f) => path.join(changesetDir, f));
+}
+
+function splitChangelog(text) {
+  // Split off the top-level "# Changelog" heading + lead matter (everything
+  // before the first "## [version]" block) from the rest. The rest is the
+  // priorChangelog passed into renderChangelog. The "## [Unreleased]" block,
+  // if present, is dropped (the new release replaces it).
+  const lines = text.split(/\r?\n/);
+  const firstReleaseIdx = lines.findIndex((l) => /^##\s+\[/.test(l));
+  if (firstReleaseIdx === -1) {
+    return { lead: text.replace(/\s+$/, ''), prior: '' };
+  }
+  const lead = lines.slice(0, firstReleaseIdx).join('\n').replace(/\s+$/, '');
+  let priorStart = firstReleaseIdx;
+  // Skip the [Unreleased] block if present — it's a placeholder, not a release.
+  if (/^##\s+\[Unreleased\]/i.test(lines[firstReleaseIdx])) {
+    let j = firstReleaseIdx + 1;
+    while (j < lines.length && !/^##\s+\[/.test(lines[j])) j++;
+    priorStart = j;
+  }
+  const prior = lines.slice(priorStart).join('\n').trimStart();
+  return { lead, prior };
+}
+
+function cmdRender(opts) {
+  const repo = path.resolve(opts.repo);
+  const changesetDir = path.join(repo, '.changeset');
+  const changelogPath = path.join(repo, 'CHANGELOG.md');
+  const fragmentFiles = listFragmentFiles(changesetDir);
+
+  const fragments = [];
+  const failures = [];
+  for (const file of fragmentFiles) {
+    const src = fs.readFileSync(file, 'utf8');
+    const r = parseFragment(src);
+    if (r.ok) fragments.push({ ...r.fragment, file });
+    else failures.push({ file: path.relative(repo, file), reason: r.reason, detail: r.detail || null });
+  }
+
+  if (failures.length > 0) {
+    return { exitCode: 1, report: { consumed: 0, failures } };
+  }
+  if (fragments.length === 0) {
+    return { exitCode: 0, report: { consumed: 0, failures: [] } };
+  }
+
+  const priorText = fs.existsSync(changelogPath) ? fs.readFileSync(changelogPath, 'utf8') : '';
+  const { lead, prior } = splitChangelog(priorText);
+
+  const ir = renderChangelog({
+    fragments,
+    version: opts.version,
+    date: opts.date,
+    priorChangelog: prior || null,
+  });
+  const releaseBlock = serializeChangelog(ir);
+  const out = [
+    lead || '# Changelog',
+    '',
+    '## [Unreleased]',
+    '',
+    releaseBlock.replace(/\s+$/, ''),
+    '',
+  ].join('\n');
+
+  fs.writeFileSync(changelogPath, out);
+
+  // Delete consumed fragments. If any unlink fails the changelog is written
+  // but the fragment is still on disk, so a re-run would double-consume it.
+  // Surface the partial-failure as exitCode=1 with structured detail so the
+  // operator can manually clean up before retrying.
+  const deleteFailures = [];
+  for (const f of fragments) {
+    try {
+      fs.unlinkSync(f.file);
+    } catch (e) {
+      deleteFailures.push({
+        file: path.relative(repo, f.file),
+        reason: 'fail_fragment_delete',
+        detail: e.code || e.message,
+      });
+    }
+  }
+
+  return {
+    exitCode: deleteFailures.length > 0 ? 1 : 0,
+    report: {
+      consumed: fragments.length - deleteFailures.length,
+      failures: deleteFailures,
+      release: { version: opts.version, date: opts.date },
+    },
+  };
+}
+
+function main() {
+  const parsed = parseArgs(process.argv.slice(2));
+  if (!parsed.ok) {
+    process.stderr.write(`${parsed.error}\n`);
+    process.stderr.write('usage: changeset/cli.cjs render --repo <dir> --version V --date D [--json]\n');
+    process.exit(2);
+  }
+  const { opts } = parsed;
+  if (opts.cmd !== 'render') {
+    process.stderr.write('usage: changeset/cli.cjs render --repo <dir> --version V --date D [--json]\n');
+    process.exit(2);
+  }
+  if (!opts.version || !opts.date) {
+    process.stderr.write('--version and --date are required for render\n');
+    process.exit(2);
+  }
+
+  const { exitCode, report } = cmdRender(opts);
+  if (opts.json) {
+    process.stdout.write(JSON.stringify(report, null, 2) + '\n');
+  } else {
+    process.stdout.write(`Consumed: ${report.consumed} fragment(s)\n`);
+    if (report.failures.length > 0) {
+      process.stdout.write(`Failures: ${report.failures.length}\n`);
+      for (const f of report.failures) {
+        process.stdout.write(`  ${f.file}: ${f.reason}${f.detail ? ` (${f.detail})` : ''}\n`);
+      }
+    }
+  }
+  process.exit(exitCode);
+}
+
+if (require.main === module) main();
+
+module.exports = { cmdRender, parseArgs, splitChangelog, listFragmentFiles };
diff --git a/scripts/changeset/lint.cjs b/scripts/changeset/lint.cjs
new file mode 100755
index 000000000..51b54e3fe
--- /dev/null
+++ b/scripts/changeset/lint.cjs
@@ -0,0 +1,110 @@
+#!/usr/bin/env node
+'use strict';
+
+/**
+ * Changeset-fragment lint (#2975).
+ *
+ * Pure verdict function evaluateLint({ changedFiles, labels }) returns
+ * { ok, reason } using the LINT_REASON enum. The CLI wrapper calls it with
+ * the PR diff (via `git diff --name-only origin/main...HEAD` or the GitHub
+ * Actions event payload) and the labels list (via the GitHub event).
+ *
+ * Tests assert on the typed verdict, never on free text.
+ */
+
+const LINT_REASON = Object.freeze({
+  OK_FRAGMENT_PRESENT: 'ok_fragment_present',
+  OK_OPT_OUT_LABEL: 'ok_opt_out_label',
+  OK_NO_USER_FACING_CHANGES: 'ok_no_user_facing_changes',
+  FAIL_MISSING_FRAGMENT: 'fail_missing_fragment',
+});
+
+const OPT_OUT_LABEL = 'no-changelog';
+
+// Files counted as "user-facing" — touching any of these requires either a
+// fragment or an explicit opt-out label. Test/CI/docs/lock files do not.
+const USER_FACING_PREFIXES = [
+  'bin/',
+  'get-shit-done/',
+  'agents/',
+  'commands/',
+  'hooks/',
+  'sdk/src/',
+  'sdk/prompts/',
+];
+
+// Exact-match user-facing files. Any direct edit to one of these without a
+// fragment also fails the lint — closes the bypass where a contributor edits
+// CHANGELOG.md directly to sneak past the new workflow.
+const USER_FACING_FILES = new Set(['CHANGELOG.md']);
+
+function isUserFacing(file) {
+  if (USER_FACING_FILES.has(file)) return true;
+  return USER_FACING_PREFIXES.some((p) => file.startsWith(p));
+}
+
+function isFragment(file) {
+  return /^\.changeset\/[^/]+\.md$/.test(file) && !file.endsWith('/README.md');
+}
+
+function evaluateLint({ changedFiles, labels }) {
+  if (changedFiles.some(isFragment)) {
+    return { ok: true, reason: LINT_REASON.OK_FRAGMENT_PRESENT };
+  }
+  if (labels.includes(OPT_OUT_LABEL)) {
+    return { ok: true, reason: LINT_REASON.OK_OPT_OUT_LABEL };
+  }
+  if (!changedFiles.some(isUserFacing)) {
+    return { ok: true, reason: LINT_REASON.OK_NO_USER_FACING_CHANGES };
+  }
+  return { ok: false, reason: LINT_REASON.FAIL_MISSING_FRAGMENT };
+}
+
+function main() {
+  const fs = require('node:fs');
+  const cp = require('node:child_process');
+  // GitHub Actions event payload path
+  const eventPath = process.env.GITHUB_EVENT_PATH;
+  let labels = [];
+  if (eventPath && fs.existsSync(eventPath)) {
+    try {
+      const event = JSON.parse(fs.readFileSync(eventPath, 'utf8'));
+      labels = (event.pull_request?.labels || []).map((l) => l.name);
+    } catch { /* fall through */ }
+  }
+  const base = process.env.GITHUB_BASE_REF || 'main';
+  let changedFiles = [];
+  try {
+    // Use execFileSync with an argv array — the base ref is interpolated
+    // into a refspec argument, but execFileSync does not invoke a shell, so
+    // even a malicious GITHUB_BASE_REF cannot inject shell syntax. The
+    // refspec-bound metacharacters that git itself rejects (e.g. spaces in
+    // ref names) are caught by git's own arg parser.
+    const out = cp.execFileSync(
+      'git',
+      ['diff', '--name-only', `origin/${base}...HEAD`],
+      { encoding: 'utf8' },
+    );
+    changedFiles = out.split('\n').filter(Boolean);
+  } catch (e) {
+    process.stderr.write(`could not compute diff: ${e.message}\n`);
+    process.exit(2);
+  }
+
+  const verdict = evaluateLint({ changedFiles, labels });
+  if (process.argv.includes('--json')) {
+    process.stdout.write(JSON.stringify({ ...verdict, changedFiles, labels }, null, 2) + '\n');
+  } else if (verdict.ok) {
+    process.stdout.write(`ok changeset-lint: ${verdict.reason}\n`);
+  } else {
+    process.stderr.write(`\nERROR changeset-lint: ${verdict.reason}\n`);
+    process.stderr.write(`PR touches user-facing files but does not include a .changeset/*.md fragment.\n`);
+    process.stderr.write(`Run \`npm run changeset\` to create one, or add the \`${OPT_OUT_LABEL}\` label\n`);
+    process.stderr.write(`if this PR genuinely has no user-facing impact (test refactor, CI tweak, etc.).\n`);
+  }
+  process.exit(verdict.ok ? 0 : 1);
+}
+
+if (require.main === module) main();
+
+module.exports = { evaluateLint, LINT_REASON, OPT_OUT_LABEL, isUserFacing, isFragment };
diff --git a/scripts/changeset/new.cjs b/scripts/changeset/new.cjs
new file mode 100755
index 000000000..3df75d023
--- /dev/null
+++ b/scripts/changeset/new.cjs
@@ -0,0 +1,137 @@
+#!/usr/bin/env node
+'use strict';
+
+/**
+ * Scaffolds a new changeset fragment (#2975).
+ *
+ *   npm run changeset -- --type Fixed --pr 1234 --body "fix the thing"
+ *
+ * Writes `.changeset/<adjective>-<noun>-<noun>.md` with frontmatter
+ * + body. The random three-word filename minimizes filename collision
+ * across concurrent PRs.
+ */
+
+const fs = require('node:fs');
+const path = require('node:path');
+
+// Small word lists — keep the function simple and dependency-free.
+// Together this gives ~40 * 40 * 40 = 64,000 distinct names. The lint
+// rejects any duplicate filename, so collisions are caught even when
+// the random draw repeats.
+const ADJECTIVES = [
+  'silly', 'brave', 'calm', 'eager', 'gentle', 'happy', 'jolly', 'kind',
+  'lively', 'merry', 'nimble', 'plucky', 'quick', 'sturdy', 'witty', 'zesty',
+  'bold', 'clever', 'daring', 'fierce', 'graceful', 'humble', 'lucky', 'noble',
+  'proud', 'rapid', 'sharp', 'tidy', 'vivid', 'wise', 'agile', 'curious',
+  'eager', 'gallant', 'mellow', 'patient', 'serene', 'steady', 'sturdy', 'sunny',
+];
+const NOUNS_A = [
+  'bears', 'birds', 'cats', 'dogs', 'elks', 'foxes', 'goats', 'hawks',
+  'ibex', 'jays', 'koalas', 'lynx', 'moles', 'newts', 'otters', 'pumas',
+  'quails', 'rams', 'seals', 'tigers', 'voles', 'wolves', 'yaks', 'zebras',
+  'badgers', 'cranes', 'deer', 'eagles', 'finches', 'geese', 'herons', 'jaguars',
+  'lemurs', 'mice', 'orcas', 'pandas', 'ravens', 'sloths', 'tunas', 'wasps',
+];
+const NOUNS_B = [
+  'dance', 'sing', 'leap', 'run', 'jump', 'climb', 'fly', 'swim',
+  'rest', 'wake', 'roam', 'greet', 'wander', 'gather', 'forage', 'travel',
+  'glide', 'sprint', 'tumble', 'wave', 'cheer', 'rally', 'parade', 'march',
+  'hop', 'frolic', 'caper', 'romp', 'zip', 'dart', 'snooze', 'munch',
+  'chatter', 'squeak', 'howl', 'bark', 'purr', 'roar', 'hum', 'click',
+];
+
+function pick(arr) {
+  return arr[Math.floor(Math.random() * arr.length)];
+}
+
+function generateFragmentName() {
+  return `${pick(ADJECTIVES)}-${pick(NOUNS_A)}-${pick(NOUNS_B)}`;
+}
+
+// Allowed Keep-a-Changelog section types. Used by both scaffoldFragment
+// (sanitization at write time) and parse.cjs (validation at consume time).
+const ALLOWED_TYPES = new Set(['Added', 'Changed', 'Deprecated', 'Removed', 'Fixed', 'Security']);
+
+function scaffoldFragment({ repo, type, pr, body }) {
+  // Sanitize: reject any type value not on the allowlist BEFORE embedding it
+  // in frontmatter. A newline in `type` would corrupt the fragment; an
+  // unrecognized value would be rejected later by parse.cjs but with a
+  // confusing diagnostic. Catch both at the write boundary.
+  if (!ALLOWED_TYPES.has(type)) {
+    throw new Error(
+      `scaffoldFragment: type=${JSON.stringify(type)} is not one of [${[...ALLOWED_TYPES].join(', ')}]`,
+    );
+  }
+  const dir = path.join(repo, '.changeset');
+  fs.mkdirSync(dir, { recursive: true });
+  const content = `---\ntype: ${type}\npr: ${pr}\n---\n${body}\n`;
+  // Atomic create: writeFileSync with `flag: 'wx'` fails (EEXIST) when the
+  // file already exists, so concurrent invocations can't race past
+  // `existsSync` and overwrite each other. Re-roll the random name on
+  // collision; fail loudly after exhausting the retry budget.
+  for (let i = 0; i < 16; i++) {
+    const name = generateFragmentName();
+    const target = path.join(dir, `${name}.md`);
+    try {
+      fs.writeFileSync(target, content, { flag: 'wx' });
+      return target;
+    } catch (e) {
+      if (e.code !== 'EEXIST') throw e;
+      // collision — try another random draw
+    }
+  }
+  throw new Error(
+    'scaffoldFragment: 16 random filename draws all collided; ' +
+    'expand the word lists or investigate corrupted .changeset/ state',
+  );
+}
+
+function parseArgs(argv) {
+  const opts = { type: null, pr: null, body: null, repo: process.cwd() };
+  // Validate flag values: argv[++i] could be undefined (flag with no value)
+  // or another flag (silently misparsed). Match the cli.cjs convention: return
+  // { ok: true, opts } on success, { ok: false, error } on malformed input.
+  const requireValue = (flag, i) => {
+    const v = argv[i + 1];
+    if (v === undefined || v.startsWith('--')) {
+      return { ok: false, error: `missing value for ${flag}` };
+    }
+    return { ok: true, value: v };
+  };
+
+  for (let i = 0; i < argv.length; i++) {
+    const a = argv[i];
+    if (a === '--type' || a === '--pr' || a === '--body' || a === '--repo') {
+      const r = requireValue(a, i);
+      if (!r.ok) return { ok: false, error: r.error };
+      if (a === '--type') opts.type = r.value;
+      else if (a === '--pr') opts.pr = Number(r.value);
+      else if (a === '--body') opts.body = r.value;
+      else if (a === '--repo') opts.repo = r.value;
+      i++;
+      continue;
+    }
+    return { ok: false, error: `unknown argument: ${a}` };
+  }
+  return { ok: true, opts };
+}
+
+function main() {
+  const parsed = parseArgs(process.argv.slice(2));
+  if (!parsed.ok) {
+    process.stderr.write(`${parsed.error}\n`);
+    process.stderr.write('usage: changeset/new.cjs --type <Fixed|Added|...> --pr NNNN --body "..."\n');
+    process.exit(2);
+  }
+  const { opts } = parsed;
+  if (!opts.type || !opts.pr || !opts.body) {
+    process.stderr.write('usage: changeset/new.cjs --type <Fixed|Added|...> --pr NNNN --body "..."\n');
+    process.exit(2);
+  }
+  const file = scaffoldFragment(opts);
+  process.stdout.write(`${path.relative(process.cwd(), file)}\n`);
+}
+
+if (require.main === module) main();
+
+module.exports = { generateFragmentName, scaffoldFragment, parseArgs, ALLOWED_TYPES };
diff --git a/scripts/changeset/parse.cjs b/scripts/changeset/parse.cjs
new file mode 100644
index 000000000..b35ceacff
--- /dev/null
+++ b/scripts/changeset/parse.cjs
@@ -0,0 +1,60 @@
+'use strict';
+
+/**
+ * Parses a changeset fragment file (text → typed record).
+ *
+ *   ---
+ *   type: Fixed
+ *   pr: 2975
+ *   ---
+ *   <markdown body>
+ *
+ * Returns { ok: true, fragment: { type, pr, body } } on success,
+ * { ok: false, reason: FRAGMENT_ERROR.X, detail } on failure.
+ *
+ * The reason field is a frozen enum so tests assert on stable codes,
+ * not free-text error messages (CONTRIBUTING.md: "Prohibited: Raw
+ * Text Matching on Test Outputs").
+ */
+const FRAGMENT_ERROR = Object.freeze({
+  MISSING_FRONTMATTER: 'missing_frontmatter',
+  MISSING_TYPE: 'missing_type',
+  INVALID_TYPE: 'invalid_type',
+  MISSING_PR: 'missing_pr',
+  INVALID_PR: 'invalid_pr',
+  EMPTY_BODY: 'empty_body',
+});
+
+const ALLOWED_TYPES = new Set(['Added', 'Changed', 'Deprecated', 'Removed', 'Fixed', 'Security']);
+
+function parseFragment(src) {
+  const fmMatch = src.match(/^---\r?\n([\s\S]*?)\r?\n---\r?\n([\s\S]*)$/);
+  if (!fmMatch) return { ok: false, reason: FRAGMENT_ERROR.MISSING_FRONTMATTER };
+  const [, fmBlock, body] = fmMatch;
+
+  const fields = {};
+  for (const line of fmBlock.split(/\r?\n/)) {
+    const m = line.match(/^([a-zA-Z0-9_-]+):\s*(.*)$/);
+    if (m) fields[m[1]] = m[2].trim();
+  }
+
+  if (!fields.type) return { ok: false, reason: FRAGMENT_ERROR.MISSING_TYPE };
+  if (!ALLOWED_TYPES.has(fields.type)) {
+    return { ok: false, reason: FRAGMENT_ERROR.INVALID_TYPE, detail: fields.type };
+  }
+  if (!fields.pr) return { ok: false, reason: FRAGMENT_ERROR.MISSING_PR };
+  const pr = Number(fields.pr);
+  if (!Number.isInteger(pr) || pr <= 0) {
+    return { ok: false, reason: FRAGMENT_ERROR.INVALID_PR, detail: fields.pr };
+  }
+  // Use trim() only for the emptiness check; preserve the body verbatim
+  // (including significant leading/trailing whitespace, code blocks, etc.)
+  // so render → serialize round-trips exactly. Strip only a single trailing
+  // newline added by editors so byte-equality holds for typical fragments.
+  if (!body.trim()) return { ok: false, reason: FRAGMENT_ERROR.EMPTY_BODY };
+  const verbatimBody = body.endsWith('\n') ? body.slice(0, -1) : body;
+
+  return { ok: true, fragment: { type: fields.type, pr, body: verbatimBody } };
+}
+
+module.exports = { parseFragment, FRAGMENT_ERROR, ALLOWED_TYPES };
diff --git a/scripts/changeset/render.cjs b/scripts/changeset/render.cjs
new file mode 100644
index 000000000..babcab34e
--- /dev/null
+++ b/scripts/changeset/render.cjs
@@ -0,0 +1,34 @@
+'use strict';
+
+/**
+ * Pure renderer for the changeset-fragment workflow (#2975).
+ *
+ * Returns a typed Changelog IR — no file I/O. The IR is the contract that
+ * tests assert on; the markdown serializer is a separate concern.
+ *
+ *   IR shape: {
+ *     releaseHeader: { version: string, date: string },
+ *     sections: [{ type: string, bullets: [{ pr: number, body: string }] }],
+ *     priorChangelog: string | null,
+ *   }
+ */
+// Keep a Changelog (https://keepachangelog.com) standard section order.
+const SECTION_ORDER = ['Added', 'Changed', 'Deprecated', 'Removed', 'Fixed', 'Security'];
+
+function renderChangelog({ fragments, version, date, priorChangelog }) {
+  const byType = new Map();
+  for (const f of fragments) {
+    if (!byType.has(f.type)) byType.set(f.type, []);
+    byType.get(f.type).push({ pr: f.pr, body: f.body });
+  }
+  const sections = SECTION_ORDER
+    .filter((type) => byType.has(type))
+    .map((type) => ({ type, bullets: byType.get(type) }));
+  return {
+    releaseHeader: { version, date },
+    sections,
+    priorChangelog: priorChangelog || null,
+  };
+}
+
+module.exports = { renderChangelog };
diff --git a/scripts/changeset/serialize.cjs b/scripts/changeset/serialize.cjs
new file mode 100644
index 000000000..a70265e72
--- /dev/null
+++ b/scripts/changeset/serialize.cjs
@@ -0,0 +1,74 @@
+'use strict';
+
+/**
+ * Markdown serializer + parser for the changelog IR. The two are inverses
+ * over the well-formed subset; tests assert via round-trip (parse(serialize(ir)))
+ * rather than by inspecting serialized text — see CONTRIBUTING.md
+ * "Prohibited: Raw Text Matching on Test Outputs".
+ *
+ * Serialized form (Keep a Changelog):
+ *
+ *   ## [1.42.0] - 2026-05-01
+ *
+ *   ### Fixed
+ *
+ *   - body of the bullet (#NNNN)
+ *
+ *   <priorChangelog appended verbatim>
+ */
+
+function serializeChangelog(ir) {
+  const lines = [];
+  const { version, date } = ir.releaseHeader;
+  lines.push(`## [${version}] - ${date}`);
+  lines.push('');
+  for (const section of ir.sections) {
+    lines.push(`### ${section.type}`);
+    lines.push('');
+    for (const b of section.bullets) {
+      lines.push(`- ${b.body} (#${b.pr})`);
+    }
+    lines.push('');
+  }
+  let out = lines.join('\n');
+  if (ir.priorChangelog) {
+    out += '\n' + ir.priorChangelog;
+  }
+  return out;
+}
+
+/**
+ * Inverse parser: extracts the structured releases from a CHANGELOG.md
+ * text. Returns { releases: [{ version, date, sections: [{ type, bullets:
+ * [{ pr, body }] }] }] }. Tolerates the actual repo's CHANGELOG dialect.
+ */
+function parseChangelog(text) {
+  const releases = [];
+  const lines = text.split(/\r?\n/);
+  let cur = null;
+  let curSection = null;
+  for (const line of lines) {
+    const releaseMatch = line.match(/^##\s+\[([^\]]+)\](?:\s*-\s*(\S+))?/);
+    if (releaseMatch) {
+      cur = { version: releaseMatch[1], date: releaseMatch[2] || null, sections: [] };
+      curSection = null;
+      releases.push(cur);
+      continue;
+    }
+    if (!cur) continue;
+    const sectionMatch = line.match(/^###\s+(.+?)\s*$/);
+    if (sectionMatch) {
+      curSection = { type: sectionMatch[1], bullets: [] };
+      cur.sections.push(curSection);
+      continue;
+    }
+    if (!curSection) continue;
+    const bulletMatch = line.match(/^-\s+(.*?)\s*\(#(\d+)\)\s*$/);
+    if (bulletMatch) {
+      curSection.bullets.push({ body: bulletMatch[1], pr: Number(bulletMatch[2]) });
+    }
+  }
+  return { releases };
+}
+
+module.exports = { serializeChangelog, parseChangelog };
diff --git a/tests/changeset-cli.test.cjs b/tests/changeset-cli.test.cjs
new file mode 100644
index 000000000..f4579e064
--- /dev/null
+++ b/tests/changeset-cli.test.cjs
@@ -0,0 +1,74 @@
+'use strict';
+process.env.GSD_TEST_MODE = '1';
+
+const { test, describe, before, after } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const os = require('node:os');
+const path = require('node:path');
+const cp = require('node:child_process');
+
+const ROOT = path.join(__dirname, '..');
+const SCRIPT = path.join(ROOT, 'scripts', 'changeset', 'cli.cjs');
+const { parseChangelog } = require(path.join(ROOT, 'scripts', 'changeset', 'serialize.cjs'));
+
+let tmp;
+
+function writeFragment(name, type, pr, body) {
+  fs.mkdirSync(path.join(tmp, '.changeset'), { recursive: true });
+  fs.writeFileSync(
+    path.join(tmp, '.changeset', `${name}.md`),
+    `---\ntype: ${type}\npr: ${pr}\n---\n${body}\n`,
+  );
+}
+
+function runRender(args = []) {
+  const r = cp.spawnSync(
+    process.execPath,
+    [SCRIPT, 'render', '--repo', tmp, ...args, '--json'],
+    { encoding: 'utf8' },
+  );
+  return {
+    status: r.status,
+    report: r.stdout && r.stdout.length ? JSON.parse(r.stdout) : null,
+    stderr: r.stderr || '',
+  };
+}
+
+before(() => { tmp = fs.mkdtempSync(path.join(os.tmpdir(), 'gsd-changeset-')); });
+after(() => { fs.rmSync(tmp, { recursive: true, force: true }); });
+
+describe('changeset cli render: file-I/O wrapper (#2975)', () => {
+  test('exits 0 with consumed=N when N fragments are folded into CHANGELOG.md and deleted', () => {
+    fs.rmSync(path.join(tmp, '.changeset'), { recursive: true, force: true });
+    fs.writeFileSync(
+      path.join(tmp, 'CHANGELOG.md'),
+      '# Changelog\n\n## [Unreleased]\n\n## [1.0.0] - 2026-01-01\n\n### Fixed\n\n- prior fix (#1)\n',
+    );
+    writeFragment('aaa-bbb-ccc', 'Fixed', 100, 'fragment-driven fix.');
+    writeFragment('ddd-eee-fff', 'Added', 101, 'fragment-driven feature.');
+
+    const r = runRender(['--version', '1.1.0', '--date', '2026-05-01']);
+    assert.equal(r.status, 0, `stderr=${r.stderr}`);
+    assert.equal(r.report.consumed, 2);
+    assert.equal(r.report.failures.length, 0);
+
+    // Round-trip: parsing the resulting CHANGELOG must reflect the new release
+    // and preserve the prior one.
+    const text = fs.readFileSync(path.join(tmp, 'CHANGELOG.md'), 'utf8');
+    const parsed = parseChangelog(text);
+    const v110 = parsed.releases.find((r) => r.version === '1.1.0');
+    assert.ok(v110, 'new 1.1.0 release present');
+    assert.deepEqual(
+      v110.sections.map((s) => ({ type: s.type, prs: s.bullets.map((b) => b.pr) })),
+      [{ type: 'Added', prs: [101] }, { type: 'Fixed', prs: [100] }],
+    );
+    const v100 = parsed.releases.find((r) => r.version === '1.0.0');
+    assert.ok(v100, 'prior 1.0.0 release preserved');
+    assert.equal(v100.sections[0].bullets[0].pr, 1);
+
+    // Fragments deleted after consumption.
+    const remaining = fs.readdirSync(path.join(tmp, '.changeset'));
+    assert.deepEqual(remaining.filter((f) => f.endsWith('.md')), []);
+  });
+});
diff --git a/tests/changeset-lint.test.cjs b/tests/changeset-lint.test.cjs
new file mode 100644
index 000000000..6979c7ca3
--- /dev/null
+++ b/tests/changeset-lint.test.cjs
@@ -0,0 +1,68 @@
+'use strict';
+process.env.GSD_TEST_MODE = '1';
+
+const { test, describe } = require('node:test');
+const assert = require('node:assert/strict');
+const path = require('node:path');
+
+const { evaluateLint, LINT_REASON } = require(path.join(__dirname, '..', 'scripts', 'changeset', 'lint.cjs'));
+
+// evaluateLint is a pure function over file lists + label list — no fs, no git.
+// Tests assert on the structured verdict: { ok: bool, reason: LINT_REASON.X }.
+
+describe('changeset lint: pure verdict (#2975)', () => {
+  test('LINT_REASON enum exposes the documented codes', () => {
+    assert.deepEqual(
+      Object.keys(LINT_REASON).sort(),
+      ['OK_FRAGMENT_PRESENT', 'OK_NO_USER_FACING_CHANGES', 'OK_OPT_OUT_LABEL', 'FAIL_MISSING_FRAGMENT'].sort(),
+    );
+  });
+
+  test('OK_FRAGMENT_PRESENT when the diff includes a new .changeset/*.md', () => {
+    const verdict = evaluateLint({
+      changedFiles: ['bin/install.js', '.changeset/silly-bears-dance.md'],
+      labels: [],
+    });
+    assert.deepEqual(verdict, { ok: true, reason: LINT_REASON.OK_FRAGMENT_PRESENT });
+  });
+
+  test('FAIL_MISSING_FRAGMENT when user-facing files change without a fragment', () => {
+    const verdict = evaluateLint({
+      changedFiles: ['bin/install.js', 'tests/foo.test.cjs'],
+      labels: [],
+    });
+    assert.deepEqual(verdict, { ok: false, reason: LINT_REASON.FAIL_MISSING_FRAGMENT });
+  });
+
+  test('OK_OPT_OUT_LABEL when no-changelog label present, even with user-facing changes', () => {
+    const verdict = evaluateLint({
+      changedFiles: ['bin/install.js'],
+      labels: ['no-changelog'],
+    });
+    assert.deepEqual(verdict, { ok: true, reason: LINT_REASON.OK_OPT_OUT_LABEL });
+  });
+
+  test('OK_NO_USER_FACING_CHANGES when only test/ci/doc files change', () => {
+    const verdict = evaluateLint({
+      changedFiles: ['tests/foo.test.cjs', '.github/workflows/x.yml', 'docs/x.md'],
+      labels: [],
+    });
+    assert.deepEqual(verdict, { ok: true, reason: LINT_REASON.OK_NO_USER_FACING_CHANGES });
+  });
+
+  test('FAIL_MISSING_FRAGMENT when CHANGELOG.md is edited directly (closes the workflow bypass)', () => {
+    const verdict = evaluateLint({
+      changedFiles: ['CHANGELOG.md'],
+      labels: [],
+    });
+    assert.deepEqual(verdict, { ok: false, reason: LINT_REASON.FAIL_MISSING_FRAGMENT });
+  });
+
+  test('a fragment alone (no source change) is OK_FRAGMENT_PRESENT — fragment-only PR is allowed', () => {
+    const verdict = evaluateLint({
+      changedFiles: ['.changeset/silly-bears-dance.md'],
+      labels: [],
+    });
+    assert.deepEqual(verdict, { ok: true, reason: LINT_REASON.OK_FRAGMENT_PRESENT });
+  });
+});
diff --git a/tests/changeset-new.test.cjs b/tests/changeset-new.test.cjs
new file mode 100644
index 000000000..9bc3bd5ce
--- /dev/null
+++ b/tests/changeset-new.test.cjs
@@ -0,0 +1,95 @@
+'use strict';
+process.env.GSD_TEST_MODE = '1';
+
+const { test, describe, before, after } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const os = require('node:os');
+const path = require('node:path');
+
+const ROOT = path.join(__dirname, '..');
+const { generateFragmentName, scaffoldFragment, parseFragment } = (() => {
+  const newCs = require(path.join(ROOT, 'scripts', 'changeset', 'new.cjs'));
+  const parse = require(path.join(ROOT, 'scripts', 'changeset', 'parse.cjs'));
+  return { ...newCs, parseFragment: parse.parseFragment };
+})();
+
+let tmp;
+before(() => { tmp = fs.mkdtempSync(path.join(os.tmpdir(), 'gsd-new-changeset-')); });
+after(() => { fs.rmSync(tmp, { recursive: true, force: true }); });
+
+describe('changeset new: name generator + scaffold writer (#2975)', () => {
+  test('generateFragmentName returns three lowercase words separated by hyphens', () => {
+    const name = generateFragmentName();
+    const parts = name.split('-');
+    assert.equal(parts.length, 3);
+    for (const p of parts) {
+      assert.match(p, /^[a-z]+$/);
+    }
+  });
+
+  test('scaffoldFragment writes a parseable fragment file with the supplied type and pr', () => {
+    const file = scaffoldFragment({
+      repo: tmp,
+      type: 'Fixed',
+      pr: 9999,
+      body: 'this is a placeholder body that the contributor will replace.',
+    });
+
+    // Filesystem facts: file exists in .changeset/, is a regular file, is non-empty.
+    const stat = fs.statSync(file);
+    assert.ok(stat.isFile());
+    assert.ok(stat.size > 0);
+    assert.equal(path.dirname(file), path.join(tmp, '.changeset'));
+
+    // Content fact: the file is a valid fragment per the parser. We do NOT
+    // substring-match the file text; we round-trip it through parseFragment
+    // and assert on the typed result.
+    const src = fs.readFileSync(file, 'utf8');
+    const parsed = parseFragment(src);
+    assert.equal(parsed.ok, true);
+    assert.deepEqual(parsed.fragment, {
+      type: 'Fixed',
+      pr: 9999,
+      body: 'this is a placeholder body that the contributor will replace.',
+    });
+  });
+
+  test('two consecutive scaffoldFragment calls in the same dir produce different filenames (no collisions in normal use)', () => {
+    const a = scaffoldFragment({ repo: tmp, type: 'Added', pr: 1, body: 'aaa.' });
+    const b = scaffoldFragment({ repo: tmp, type: 'Added', pr: 2, body: 'bbb.' });
+    assert.notEqual(path.basename(a), path.basename(b));
+  });
+
+  test('rejects type values not on the Keep-a-Changelog allowlist (sanitization)', () => {
+    // Includes the newline-injection case from the CR finding.
+    for (const badType of ['Refactored', 'fixed', 'Fixed\ntype: Added', 'Fixed; rm -rf /', '']) {
+      assert.throws(
+        () => scaffoldFragment({ repo: tmp, type: badType, pr: 1, body: 'x.' }),
+        /not one of \[Added, Changed, Deprecated, Removed, Fixed, Security\]/,
+        `bad type ${JSON.stringify(badType)} should be rejected`,
+      );
+    }
+  });
+
+  test('parseArgs returns { ok: false, error } when --repo is missing its value', () => {
+    const { parseArgs } = require(path.join(ROOT, 'scripts', 'changeset', 'new.cjs'));
+    const r = parseArgs(['--type', 'Fixed', '--pr', '1', '--body', 'x.', '--repo']);
+    assert.equal(r.ok, false);
+    assert.equal(r.error, 'missing value for --repo');
+  });
+
+  test('parseArgs returns { ok: false, error } when a flag value is itself another flag', () => {
+    const { parseArgs } = require(path.join(ROOT, 'scripts', 'changeset', 'new.cjs'));
+    const r = parseArgs(['--type', 'Fixed', '--repo', '--pr', '1', '--body', 'x.']);
+    assert.equal(r.ok, false);
+    assert.equal(r.error, 'missing value for --repo');
+  });
+
+  test('parseArgs returns { ok: true, opts } on a well-formed argv', () => {
+    const { parseArgs } = require(path.join(ROOT, 'scripts', 'changeset', 'new.cjs'));
+    const r = parseArgs(['--type', 'Fixed', '--pr', '42', '--body', 'a body', '--repo', '/tmp/x']);
+    assert.equal(r.ok, true);
+    assert.deepEqual(r.opts, { type: 'Fixed', pr: 42, body: 'a body', repo: '/tmp/x' });
+  });
+});
diff --git a/tests/changeset-parse.test.cjs b/tests/changeset-parse.test.cjs
new file mode 100644
index 000000000..ff3642d41
--- /dev/null
+++ b/tests/changeset-parse.test.cjs
@@ -0,0 +1,56 @@
+'use strict';
+process.env.GSD_TEST_MODE = '1';
+
+const { test, describe } = require('node:test');
+const assert = require('node:assert/strict');
+const path = require('node:path');
+
+const { parseFragment, FRAGMENT_ERROR } = require(path.join(__dirname, '..', 'scripts', 'changeset', 'parse.cjs'));
+
+describe('changeset parse: fragment file → typed record (#2975)', () => {
+  test('returns { ok: true, fragment } for a well-formed fragment', () => {
+    const src = '---\ntype: Fixed\npr: 2975\n---\nfix the thing.\n';
+    const result = parseFragment(src);
+    assert.equal(result.ok, true);
+    assert.deepEqual(result.fragment, {
+      type: 'Fixed',
+      pr: 2975,
+      body: 'fix the thing.',
+    });
+  });
+
+  test('preserves verbatim body content (e.g. code blocks) — does not trim significant whitespace', () => {
+    const src = '---\ntype: Fixed\npr: 1\n---\n```js\nlet x = 1;\n```\n';
+    const r = parseFragment(src);
+    assert.equal(r.ok, true);
+    assert.equal(r.fragment.body, '```js\nlet x = 1;\n```');
+  });
+
+  test('exposes a frozen FRAGMENT_ERROR enum with the documented codes', () => {
+    assert.deepEqual(
+      Object.keys(FRAGMENT_ERROR).sort(),
+      ['EMPTY_BODY', 'INVALID_PR', 'INVALID_TYPE', 'MISSING_FRONTMATTER', 'MISSING_PR', 'MISSING_TYPE'],
+    );
+  });
+
+  for (const [label, src, expectedReason] of [
+    ['fails MISSING_FRONTMATTER when no frontmatter block present',
+     'just a body, no frontmatter\n', 'MISSING_FRONTMATTER'],
+    ['fails MISSING_TYPE when frontmatter omits type:',
+     '---\npr: 2975\n---\nfix.\n', 'MISSING_TYPE'],
+    ['fails INVALID_TYPE for a type not in the Keep-a-Changelog set',
+     '---\ntype: Refactored\npr: 2975\n---\nfix.\n', 'INVALID_TYPE'],
+    ['fails MISSING_PR when frontmatter omits pr:',
+     '---\ntype: Fixed\n---\nfix.\n', 'MISSING_PR'],
+    ['fails INVALID_PR when pr: is not a positive integer',
+     '---\ntype: Fixed\npr: 0\n---\nfix.\n', 'INVALID_PR'],
+    ['fails EMPTY_BODY when the body is whitespace-only',
+     '---\ntype: Fixed\npr: 2975\n---\n   \n', 'EMPTY_BODY'],
+  ]) {
+    test(label, () => {
+      const r = parseFragment(src);
+      assert.equal(r.ok, false);
+      assert.equal(r.reason, FRAGMENT_ERROR[expectedReason]);
+    });
+  }
+});
diff --git a/tests/changeset-render.test.cjs b/tests/changeset-render.test.cjs
new file mode 100644
index 000000000..dfb7c15ea
--- /dev/null
+++ b/tests/changeset-render.test.cjs
@@ -0,0 +1,48 @@
+'use strict';
+process.env.GSD_TEST_MODE = '1';
+
+const { test, describe } = require('node:test');
+const assert = require('node:assert/strict');
+const path = require('node:path');
+
+const { renderChangelog } = require(path.join(__dirname, '..', 'scripts', 'changeset', 'render.cjs'));
+
+describe('changeset render: pure renderer (#2975)', () => {
+  test('returns a structured Changelog object with a single Fixed bullet for one fragment', () => {
+    const fragments = [{ type: 'Fixed', pr: 2975, body: 'fix the thing.' }];
+    const result = renderChangelog({
+      fragments,
+      version: '1.42.0',
+      date: '2026-05-01',
+      priorChangelog: null,
+    });
+
+    assert.deepEqual(result.releaseHeader, { version: '1.42.0', date: '2026-05-01' });
+    assert.equal(result.sections.length, 1);
+    assert.deepEqual(result.sections[0], {
+      type: 'Fixed',
+      bullets: [{ pr: 2975, body: 'fix the thing.' }],
+    });
+  });
+
+  test('groups multiple fragments by type with deterministic section order (Keep a Changelog convention)', () => {
+    const fragments = [
+      { type: 'Fixed', pr: 1, body: 'fix A' },
+      { type: 'Added', pr: 2, body: 'add B' },
+      { type: 'Fixed', pr: 3, body: 'fix C' },
+      { type: 'Changed', pr: 4, body: 'change D' },
+    ];
+    const result = renderChangelog({ fragments, version: '1.0.0', date: '2026-01-01' });
+
+    assert.deepEqual(
+      result.sections.map((s) => s.type),
+      ['Added', 'Changed', 'Fixed'],
+    );
+    const fixed = result.sections.find((s) => s.type === 'Fixed');
+    assert.deepEqual(
+      fixed.bullets.map((b) => b.pr),
+      [1, 3],
+      'bullets within a section preserve fragment order',
+    );
+  });
+});
diff --git a/tests/changeset-serialize.test.cjs b/tests/changeset-serialize.test.cjs
new file mode 100644
index 000000000..1d73917b1
--- /dev/null
+++ b/tests/changeset-serialize.test.cjs
@@ -0,0 +1,72 @@
+'use strict';
+process.env.GSD_TEST_MODE = '1';
+
+const { test, describe } = require('node:test');
+const assert = require('node:assert/strict');
+const path = require('node:path');
+
+const { serializeChangelog, parseChangelog } = require(path.join(__dirname, '..', 'scripts', 'changeset', 'serialize.cjs'));
+
+// Round-trip property: serialize(IR) → parse(text) → IR equals original.
+// Tests assert on the parsed IR shape, not the serialized text contents.
+
+describe('changeset serialize: IR → markdown round-trip (#2975)', () => {
+  test('a single-section IR round-trips through serialize → parse', () => {
+    const ir = {
+      releaseHeader: { version: '1.0.0', date: '2026-01-01' },
+      sections: [
+        { type: 'Fixed', bullets: [{ pr: 1, body: 'fix something.' }] },
+      ],
+      priorChangelog: null,
+    };
+    const text = serializeChangelog(ir);
+    const back = parseChangelog(text);
+
+    assert.equal(back.releases[0].version, '1.0.0');
+    assert.equal(back.releases[0].date, '2026-01-01');
+    assert.equal(back.releases[0].sections.length, 1);
+    assert.equal(back.releases[0].sections[0].type, 'Fixed');
+    assert.equal(back.releases[0].sections[0].bullets.length, 1);
+    assert.equal(back.releases[0].sections[0].bullets[0].pr, 1);
+  });
+});
+
+describe('changeset serialize: multi-section + prior content (#2975)', () => {
+  const { serializeChangelog, parseChangelog } = require(require('node:path').join(__dirname, '..', 'scripts', 'changeset', 'serialize.cjs'));
+
+  test('round-trips an IR with three section types and multiple bullets per section', () => {
+    const ir = {
+      releaseHeader: { version: '1.42.0', date: '2026-05-01' },
+      sections: [
+        { type: 'Added', bullets: [{ pr: 1, body: 'add A' }, { pr: 2, body: 'add B' }] },
+        { type: 'Changed', bullets: [{ pr: 3, body: 'change C' }] },
+        { type: 'Fixed', bullets: [{ pr: 4, body: 'fix D' }, { pr: 5, body: 'fix E' }] },
+      ],
+      priorChangelog: null,
+    };
+    const back = parseChangelog(serializeChangelog(ir));
+    assert.equal(back.releases.length, 1);
+    assert.deepEqual(
+      back.releases[0].sections.map((s) => ({ type: s.type, prs: s.bullets.map((b) => b.pr) })),
+      [
+        { type: 'Added', prs: [1, 2] },
+        { type: 'Changed', prs: [3] },
+        { type: 'Fixed', prs: [4, 5] },
+      ],
+    );
+  });
+
+  test('prior CHANGELOG content survives serialize → parse as a separate release block', () => {
+    const priorText = '## [0.9.0] - 2025-12-01\n\n### Fixed\n\n- old fix (#100)\n';
+    const ir = {
+      releaseHeader: { version: '1.0.0', date: '2026-01-01' },
+      sections: [{ type: 'Added', bullets: [{ pr: 200, body: 'new feature' }] }],
+      priorChangelog: priorText,
+    };
+    const back = parseChangelog(serializeChangelog(ir));
+    assert.equal(back.releases.length, 2);
+    assert.equal(back.releases[0].version, '1.0.0');
+    assert.equal(back.releases[1].version, '0.9.0');
+    assert.equal(back.releases[1].sections[0].bullets[0].pr, 100);
+  });
+});