diff --git a/.changeset/curious-newts-sprint.md b/.changeset/curious-newts-sprint.md
new file mode 100644
index 000000000..4f8275043
--- /dev/null
+++ b/.changeset/curious-newts-sprint.md
@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 2894
+---
+**Releases no longer fail their own emitted-parity gate** — cutting any release ran the differential attribution check against a baseline built at a different version, so the install-time hook version stamp made all 364 emitted hook paths look like unexplained drift and every `finalize`/`rc` run hard-failed before tagging or publishing. (#2891)
diff --git a/tests/emitted-attribution.test.cjs b/tests/emitted-attribution.test.cjs
index 89349fb3c..f05ccff72 100644
--- a/tests/emitted-attribution.test.cjs
+++ b/tests/emitted-attribution.test.cjs
@@ -34,11 +34,12 @@ const test = require('node:test');
 const assert = require('node:assert/strict');
 const fs = require('node:fs');
 const path = require('node:path');
+const crypto = require('node:crypto');
 const { execFileSync } = require('node:child_process');
 const fc = require('fast-check');
 
 const { cleanup, createTempDir } = require('./helpers.cjs');
-const { BUILD_SCRIPT } = require('./helpers/install-shared.cjs');
+const { BUILD_SCRIPT, buildParityManifest, buildInstallTree, PKG_VERSION } = require('./helpers/install-shared.cjs');
 const {
   resolveChangedPaths,
   resolveBase,
@@ -57,6 +58,7 @@ const {
   touchesRuntimeRegistry,
   reconcileFamilies,
   safeDirArgs,
+  measuredPackageVersion,
 } = require('./helpers/emitted-runtime.cjs');
 
 const { EXPECTED_MANIFEST_COUNT, loadManifests } = require('./helpers/emitted-provenance.cjs');
@@ -2448,3 +2450,303 @@ test('differential attribution over the real tree', { timeout: 900_000 }, async
     `emitted-attribution failed against ${base}@${baseSha.slice(0, 12)}:\n\n${formatReport(result)}`,
   );
 });
+
+// ─── Cross-tree version normalization (#2891) ──────────────────────────────────
+//
+// #2767's `currentManifests({ repoRoot })` spawns a DIFFERENT checkout's installer
+// but, before this fix, still normalized the emitted content against THIS checkout's
+// PKG_VERSION — so a version-bumped current tree compared against an older-version
+// baseline worktree never collapsed the baseline's `// gsd-hook-version: <old>` stamp
+// to '<VERSION>', every one of that baseline's emitted files spuriously "differed",
+// and the differential attribution gate above (the real-tree test) failed with all
+// 364 emitted hook paths unattributed. These tests pin the mechanism directly against
+// `buildParityManifest`'s `pkgVersion` option and `measuredPackageVersion`, the two
+// pieces `currentManifests` composes to fix it, rather than only against the
+// expensive real-tree gate.
+
+function makeVersionStampedTree(hookVersion) {
+  const root = createTempDir('gsd-test-ppm-version-');
+  const configDir = path.join(root, 'cfg');
+  fs.mkdirSync(configDir, { recursive: true });
+  fs.writeFileSync(
+    path.join(configDir, 'hook.js'),
+    `// gsd-hook-version: ${hookVersion}\nconsole.log('hook body unchanged across versions');\n`,
+  );
+  return { root, configDir };
+}
+
+test('buildParityManifest: same content at two different pkgVersions hashes identically when each is normalized against its OWN version (#2891)', () => {
+  const a = makeVersionStampedTree('1.8.0');
+  const b = makeVersionStampedTree('1.9.0');
+  try {
+    const manifestA = buildParityManifest(a.configDir, a.root, { pkgVersion: '1.8.0' });
+    const manifestB = buildParityManifest(b.configDir, b.root, { pkgVersion: '1.9.0' });
+    assert.equal(
+      manifestA['hook.js'],
+      manifestB['hook.js'],
+      'byte-identical-apart-from-version-stamp files must hash identically once each side ' +
+      'is normalized against the version that actually produced it'
+    );
+  } finally {
+    cleanup(a.root);
+    cleanup(b.root);
+  }
+});
+
+test('buildParityManifest: hash of a measured tree does not depend on the MEASURING repo\'s own version (#2891)', () => {
+  // Reproduces the real cross-tree shape: content stamped with version X, normalized
+  // with the EXPLICIT pkgVersion of the tree that produced it (X) — never with this
+  // checkout's own PKG_VERSION (Y), which is what the pre-fix bug silently defaulted to.
+  const measuredVersion = '7.7.7';
+  assert.notEqual(
+    measuredVersion,
+    PKG_VERSION,
+    'test fixture must use a version distinct from this checkout\'s own PKG_VERSION for the assertion below to be meaningful'
+  );
+  const tree = makeVersionStampedTree(measuredVersion);
+  try {
+    const manifest = buildParityManifest(tree.configDir, tree.root, { pkgVersion: measuredVersion });
+    // The stamp must have collapsed to '<VERSION>' — if it hadn't (e.g. because the
+    // measuring repo's own PKG_VERSION had been used instead), the raw '7.7.7' would
+    // still be present pre-hash and this hash would differ from a control manifest
+    // built directly against the sentinel-substituted content.
+    const controlContent = `// gsd-hook-version: <VERSION>\nconsole.log('hook body unchanged across versions');\n`;
+    const controlHash = crypto.createHash('sha256').update(controlContent).digest('hex').slice(0, 16);
+    assert.equal(
+      manifest['hook.js'],
+      controlHash,
+      'hash must reflect the version-stamp collapsing to <VERSION> using the MEASURED tree\'s ' +
+      'own version, independent of whatever PKG_VERSION the measuring repo happens to be at'
+    );
+  } finally {
+    cleanup(tree.root);
+  }
+});
+
+test('buildParityManifest: pkgVersion guard rejects empty/undefined/null/non-string/non-semver-shaped and never corrupts the manifest (#2891)', () => {
+  const tree = makeVersionStampedTree('1.8.0');
+  try {
+    // Omitting pkgVersion entirely is legitimate (defaults to this checkout's own
+    // PKG_VERSION) and must NOT throw.
+    assert.doesNotThrow(() => buildParityManifest(tree.configDir, tree.root));
+
+    // Explicitly passing a bad value must throw — including an EXPLICIT `undefined`,
+    // which is deliberately NOT treated the same as omitting the key (see the `in`
+    // guard in install-shared.cjs: a caller-side bug that resolves a version to
+    // `undefined` must fail loudly, never silently fall back to this checkout's own
+    // version). '1' and '12' are shape failures (#2891 review FINDING 2): a
+    // non-semver-shaped string like '1' must be rejected, not silently accepted and
+    // later matched as a substring of unrelated numeric content (e.g. 'v 1.8.0 x').
+    for (const bad of ['', undefined, null, 42, '1', '12']) {
+      assert.throws(
+        () => buildParityManifest(tree.configDir, tree.root, { pkgVersion: bad }),
+        /pkgVersion must be a non-empty semver-ish string/,
+        `expected pkgVersion=${JSON.stringify(bad)} to throw`
+      );
+    }
+
+    // Corruption check: an empty pkgVersion, if it ever reached blind substring
+    // replacement, would corrupt content that merely contains matching characters.
+    // Confirm the guard fires BEFORE that — a file whose entire content is 'abc' must
+    // never make it into a manifest via a '' pkgVersion.
+    const corruptibleRoot = createTempDir('gsd-test-ppm-corrupt-');
+    const corruptibleDir = path.join(corruptibleRoot, 'cfg');
+    fs.mkdirSync(corruptibleDir, { recursive: true });
+    fs.writeFileSync(path.join(corruptibleDir, 'f.txt'), 'abc');
+    try {
+      assert.throws(
+        () => buildParityManifest(corruptibleDir, corruptibleRoot, { pkgVersion: '' }),
+        /pkgVersion must be a non-empty semver-ish string/
+      );
+    } finally {
+      cleanup(corruptibleRoot);
+    }
+  } finally {
+    cleanup(tree.root);
+  }
+});
+
+test('buildParityManifest: pkgVersion shape guard boundary — limit-1/limit/limit+1 by length (#2891 review FINDING 2)', () => {
+  const tree = makeVersionStampedTree('1.8.0');
+  try {
+    // '0.0.0' is the shortest string SEMVER_ISH_RE accepts (5 chars: MAJOR.MINOR.PATCH,
+    // all single-digit, no prerelease/build) — the "limit" case.
+    assert.doesNotThrow(
+      () => buildParityManifest(tree.configDir, tree.root, { pkgVersion: '0.0.0' }),
+      'a minimal valid MAJOR.MINOR.PATCH string must be accepted (limit)'
+    );
+    // '12' (limit+1 relative to the 1-char failure below, and still nowhere near
+    // semver-shaped) must still be rejected.
+    assert.throws(
+      () => buildParityManifest(tree.configDir, tree.root, { pkgVersion: '12' }),
+      /pkgVersion must be a non-empty semver-ish string/,
+      'a 2-char non-semver-shaped string must be rejected (limit+1 by length from \'1\')'
+    );
+    // '1' (limit-1 relative to '12') must be rejected — the concrete regression this
+    // guard exists to close: {pkgVersion:'1'} was previously ACCEPTED and rewrote
+    // 'v 1.8.0 x' to 'v <VERSION>.8.0 x' via a bare-substring match.
+    assert.throws(
+      () => buildParityManifest(tree.configDir, tree.root, { pkgVersion: '1' }),
+      /pkgVersion must be a non-empty semver-ish string/,
+      'a 1-char string must be rejected (limit-1)'
+    );
+  } finally {
+    cleanup(tree.root);
+  }
+});
+
+test('buildParityManifest: pkgVersion is honored when reachable via the PROTOTYPE CHAIN, not only as an own key (#2891 review FINDING 4)', () => {
+  const tree = makeVersionStampedTree('7.7.7');
+  try {
+    // Object.create({pkgVersion:'7.7.7'}) has NO own 'pkgVersion' key, but the key IS
+    // reachable via `in` — before the fix this silently fell through to this
+    // checkout's own PKG_VERSION (the exact silent-fallback the guard exists to
+    // prevent), reached via a different vector than an explicit own-key bad value.
+    const opts = Object.create({ pkgVersion: '7.7.7' });
+    const manifest = buildParityManifest(tree.configDir, tree.root, opts);
+    const controlContent = `// gsd-hook-version: <VERSION>\nconsole.log('hook body unchanged across versions');\n`;
+    const controlHash = crypto.createHash('sha256').update(controlContent).digest('hex').slice(0, 16);
+    assert.equal(
+      manifest['hook.js'],
+      controlHash,
+      'an inherited pkgVersion must be read and normalized against, not silently ignored in favor of this checkout\'s own PKG_VERSION'
+    );
+  } finally {
+    cleanup(tree.root);
+  }
+});
+
+test('buildParityManifest: opts guard rejects null/non-object (#2891 review FINDING 5)', () => {
+  const tree = makeVersionStampedTree('1.8.0');
+  try {
+    for (const bad of [null, 'x', 42, true, []]) {
+      assert.throws(
+        () => buildParityManifest(tree.configDir, tree.root, bad),
+        /opts must be a plain object or omitted/,
+        `expected opts=${JSON.stringify(bad)} to throw a clear message, not a raw TypeError`
+      );
+    }
+  } finally {
+    cleanup(tree.root);
+  }
+});
+
+test('buildInstallTree: no longer accepts/forwards an opts argument, so a bad third argument is silently ignored rather than reaching buildParityManifest\'s guard (#2891 review FINDINGS 5+6)', () => {
+  // FINDING 6 removed buildInstallTree's dead opts-forwarding parameter (pkgVersion
+  // never affects the emitted FILE SET, only content hashes, and no caller ever passed
+  // a third argument). A consequence: buildInstallTree(cd, root, null) — the exact
+  // FINDING 5 repro against the OLD forwarding code — no longer reaches
+  // buildParityManifest's opts guard at all; the extra argument is simply unused,
+  // consistent with ordinary JS call semantics, and buildParityManifest gets its
+  // default `{}`. This must NOT throw.
+  const tree = makeVersionStampedTree('1.8.0');
+  try {
+    assert.doesNotThrow(() => buildInstallTree(tree.configDir, tree.root, null));
+    assert.deepEqual(
+      buildInstallTree(tree.configDir, tree.root, null),
+      buildInstallTree(tree.configDir, tree.root),
+      'a discarded third argument must not change the result'
+    );
+  } finally {
+    cleanup(tree.root);
+  }
+});
+
+test('measuredPackageVersion: resolves this checkout\'s version with no repoRoot, the measured tree\'s version with one, and fails closed (#2891)', () => {
+  // No repoRoot at all (key genuinely absent): this checkout's own PKG_VERSION, no
+  // filesystem I/O.
+  assert.equal(measuredPackageVersion(), PKG_VERSION);
+  // Explicit `undefined` is the ONLY falsy value treated as "this checkout" — every
+  // OTHER falsy value ('', 0, false) is a caller-side bug and must fail closed rather
+  // than silently defaulting, consistent with `currentManifests`' installScript gate
+  // and with `buildParityManifest`'s pkgVersion guard (#2891 review FINDING 7).
+  assert.equal(measuredPackageVersion(undefined), PKG_VERSION);
+  for (const bad of ['', 0, false]) {
+    assert.throws(
+      () => measuredPackageVersion(bad),
+      /repoRoot must be a non-empty path or omitted entirely/,
+      `expected repoRoot=${JSON.stringify(bad)} to throw`
+    );
+  }
+
+  // A different tree's package.json: its OWN version, not this checkout's.
+  const measuredRoot = createTempDir('gsd-test-mpv-ok-');
+  try {
+    fs.writeFileSync(
+      path.join(measuredRoot, 'package.json'),
+      JSON.stringify({ name: 'measured-tree', version: '9.9.9' }),
+    );
+    assert.equal(measuredPackageVersion(measuredRoot), '9.9.9');
+  } finally {
+    cleanup(measuredRoot);
+  }
+
+  // Missing package.json: fails closed, never falls back to this checkout's version.
+  const missingRoot = createTempDir('gsd-test-mpv-missing-');
+  try {
+    assert.throws(() => measuredPackageVersion(missingRoot), /cannot read/);
+  } finally {
+    cleanup(missingRoot);
+  }
+
+  // Unparseable package.json.
+  const badJsonRoot = createTempDir('gsd-test-mpv-badjson-');
+  try {
+    fs.writeFileSync(path.join(badJsonRoot, 'package.json'), '{not json');
+    assert.throws(() => measuredPackageVersion(badJsonRoot), /not valid JSON/);
+  } finally {
+    cleanup(badJsonRoot);
+  }
+
+  // Version-less package.json (key ABSENT entirely) — the only branch the pre-review
+  // test suite drove.
+  const noVersionRoot = createTempDir('gsd-test-mpv-noversion-');
+  try {
+    fs.writeFileSync(path.join(noVersionRoot, 'package.json'), JSON.stringify({ name: 'no-version' }));
+    assert.throws(() => measuredPackageVersion(noVersionRoot), /no non-empty string "version" field/);
+  } finally {
+    cleanup(noVersionRoot);
+  }
+
+  // "version" key PRESENT but an empty string — a distinct branch from "absent"
+  // (`typeof '' === 'string'` but `''.length === 0`); the pre-review suite never drove
+  // it and both surviving mutants collapse this into the absent-key case (#2891 review
+  // FINDING 3).
+  const emptyVersionRoot = createTempDir('gsd-test-mpv-emptyversion-');
+  try {
+    fs.writeFileSync(path.join(emptyVersionRoot, 'package.json'), JSON.stringify({ version: '' }));
+    assert.throws(() => measuredPackageVersion(emptyVersionRoot), /no non-empty string "version" field/);
+  } finally {
+    cleanup(emptyVersionRoot);
+  }
+
+  // "version" key PRESENT but non-string (e.g. a bare JSON number) — the other branch
+  // `typeof version !== 'string'` guards, distinct from both "absent" and "empty
+  // string" (#2891 review FINDING 3).
+  const numericVersionRoot = createTempDir('gsd-test-mpv-numericversion-');
+  try {
+    fs.writeFileSync(path.join(numericVersionRoot, 'package.json'), JSON.stringify({ version: 123 }));
+    assert.throws(() => measuredPackageVersion(numericVersionRoot), /no non-empty string "version" field/);
+  } finally {
+    cleanup(numericVersionRoot);
+  }
+
+  // Unreadable package.json: monkeypatch fs.readFileSync (NEVER chmod 0o000 — root
+  // bypasses mode bits and the test would silently pass with zero coverage in root
+  // Docker/CI). Save original, override to throw, assert.throws, restore in `finally`.
+  const unreadableRoot = createTempDir('gsd-test-mpv-unreadable-');
+  try {
+    fs.writeFileSync(path.join(unreadableRoot, 'package.json'), JSON.stringify({ version: '1.0.0' }));
+    const orig = fs.readFileSync;
+    try {
+      fs.readFileSync = () => { throw new Error('injected package.json read failure'); };
+      assert.throws(() => measuredPackageVersion(unreadableRoot), /injected package\.json read failure/);
+    } finally {
+      fs.readFileSync = orig;
+    }
+    // Restoration is real, not assumed.
+    assert.equal(measuredPackageVersion(unreadableRoot), '1.0.0');
+  } finally {
+    cleanup(unreadableRoot);
+  }
+});
diff --git a/tests/helpers/emitted-runtime.cjs b/tests/helpers/emitted-runtime.cjs
index 5819fff5d..be542e698 100644
--- a/tests/helpers/emitted-runtime.cjs
+++ b/tests/helpers/emitted-runtime.cjs
@@ -42,6 +42,7 @@ const {
   MINIMUM_MANIFEST_FAMILIES,
   runMinimalInstall,
   buildParityManifest,
+  PKG_VERSION,
 } = require('./install-shared.cjs');
 
 const REPO_ROOT = path.join(__dirname, '..', '..');
@@ -601,6 +602,73 @@ function baselineSizesAtRef(base = 'origin/next') {
   return found === 0 ? null : sizes;
 }
 
+/**
+ * The package version of the tree whose emitted output is about to be measured.
+ *
+ * `bin/install.js` bakes `{{GSD_VERSION}}` -> `pkg.version` into every emitted hook,
+ * and `buildParityManifest`'s `pkgVersion` normalization exists to collapse that stamp
+ * back to '<VERSION>' so a version bump alone never moves a hash. That normalization is
+ * only correct when `pkgVersion` matches the version of the tree that PRODUCED the
+ * content being hashed — for `repoRoot`-driven cross-tree measurement (#2767, #2891)
+ * that is NOT necessarily this checkout's own `PKG_VERSION`. This helper resolves the
+ * right version for whichever tree is actually being measured.
+ *
+ * Fails closed: a missing, unreadable, unparseable, or version-less `package.json` at
+ * `repoRoot` throws rather than silently falling back to this checkout's own version —
+ * a silent fallback here is exactly the cross-tree mis-attribution bug #2891 fixes
+ * (every emitted hook path would spuriously differ, and the differential attribution
+ * gate would blame nothing for it).
+ *
+ * @param {string} [repoRoot] - absolute path to the tree being measured. Only an
+ *   OMITTED (or explicit `undefined`) repoRoot means "this checkout" and returns this
+ *   module's own PKG_VERSION with no I/O. Any OTHER falsy value (`''`, `0`, `false`) is
+ *   NOT treated as "this checkout" — it is a caller-side bug (e.g. an unresolved path
+ *   variable) and must fail closed rather than silently measuring the wrong tree,
+ *   consistent with `currentManifests`' `installScript` gate below and with how
+ *   `buildParityManifest`'s `pkgVersion` treats an explicit-but-empty value as a caller
+ *   error rather than a fallback trigger (#2891 review FINDING 7).
+ * @returns {string} non-empty package version string.
+ */
+function measuredPackageVersion(repoRoot) {
+  if (repoRoot === undefined) return PKG_VERSION;
+  if (!repoRoot) {
+    throw new Error(
+      `measuredPackageVersion: repoRoot must be a non-empty path or omitted entirely, got ${JSON.stringify(repoRoot)}. ` +
+      'An omitted/undefined repoRoot means "this checkout"; any other falsy value is treated as a caller error.'
+    );
+  }
+
+  const pkgPath = path.join(repoRoot, 'package.json');
+  let raw;
+  try {
+    raw = fs.readFileSync(pkgPath, 'utf8');
+  } catch (err) {
+    throw new Error(
+      `measuredPackageVersion: cannot read ${pkgPath} (${err.message}); cannot normalize ` +
+      'emitted version for the measured tree; a wrong version silently mis-attributes every hook.'
+    );
+  }
+
+  let parsed;
+  try {
+    parsed = JSON.parse(raw);
+  } catch (err) {
+    throw new Error(
+      `measuredPackageVersion: ${pkgPath} is not valid JSON (${err.message}); cannot normalize ` +
+      'emitted version for the measured tree; a wrong version silently mis-attributes every hook.'
+    );
+  }
+
+  const version = parsed && parsed.version;
+  if (typeof version !== 'string' || version.length === 0) {
+    throw new Error(
+      `measuredPackageVersion: ${pkgPath} has no non-empty string "version" field; cannot ` +
+      'normalize emitted version for the measured tree; a wrong version silently mis-attributes every hook.'
+    );
+  }
+  return version;
+}
+
 /**
  * Build the CURRENT emitted manifest set for real — one installer spawn per runtime.
  * This is the expensive, honest half: it reflects what the tree actually emits now,
@@ -616,14 +684,25 @@ function baselineSizesAtRef(base = 'origin/next') {
  *   base-ref worktree) so the two sides stay comparable even if the definition itself
  *   evolves — running the OTHER tree's own (older, or absent) copy of this function would
  *   defeat that.
+ *
+ *   The version normalized into '<VERSION>' inside each manifest entry is resolved via
+ *   `measuredPackageVersion(repoRoot)` — i.e. `<repoRoot>/package.json`'s own version,
+ *   NOT this checkout's — since `<repoRoot>/bin/install.js` is what stamped the emitted
+ *   content in the first place (#2891).
  */
 function currentManifests({ repoRoot } = {}) {
-  const installScript = repoRoot ? path.join(repoRoot, 'bin', 'install.js') : undefined;
+  // Gated the same way `measuredPackageVersion` gates its own repoRoot below: only an
+  // omitted/`undefined` repoRoot means "this checkout" (installScript stays the
+  // default). Any other falsy value falls through to `measuredPackageVersion`, which
+  // throws — this line never gets a chance to diverge from that same rule (#2891
+  // review FINDING 7).
+  const installScript = repoRoot !== undefined ? path.join(repoRoot, 'bin', 'install.js') : undefined;
+  const pkgVersion = measuredPackageVersion(repoRoot);
   const manifests = {};
   for (const { name, runtime, scope } of MANIFEST_FAMILIES) {
     const { configDir, root } = runMinimalInstall({ runtime, scope, installScript });
     try {
-      manifests[name] = buildParityManifest(configDir, root);
+      manifests[name] = buildParityManifest(configDir, root, { pkgVersion });
     } finally {
       cleanup(root);
     }
@@ -695,6 +774,7 @@ module.exports = {
   baselineManifestsAtRef,
   baselineSizesAtRef,
   buildBaselineAtRef,
+  measuredPackageVersion,
   currentManifests,
   currentSizes,
   readAckFile,
diff --git a/tests/helpers/install-shared.cjs b/tests/helpers/install-shared.cjs
index 3ab130a06..d684e4cbb 100644
--- a/tests/helpers/install-shared.cjs
+++ b/tests/helpers/install-shared.cjs
@@ -124,9 +124,16 @@ const SKILL_RUNTIMES = [
 // (the generator's copy was missing the realpath normalization below) and
 // shipped broken fixtures three times (#2086, #2095, #2100).
 
-// The installed package version, normalized to '<VERSION>' in hash computation so
+// This checkout's own package version — the DEFAULT normalized in hash computation so
 // the golden is stable across version bumps (the rc step runs `npm version X.Y.Z-rc.N`
 // before tests, which rebakes the version into hook files and gsd-core/VERSION).
+//
+// This is only a default. buildParityManifest's `pkgVersion` option exists precisely
+// because the tree being MEASURED is not always this checkout (#2767's `repoRoot`
+// installer-spawn path measures a DIFFERENT tree's `bin/install.js` output). The
+// version that must be normalized is always the version of the tree that PRODUCED
+// the emitted bytes, not the version of whichever checkout happens to be running this
+// test file — see the pkgVersion JSDoc on buildParityManifest below.
 const PKG_VERSION = require('../../package.json').version;
 
 // Volatile metadata files always excluded from the parity manifest.
@@ -193,10 +200,73 @@ const EXCLUDED_PREFIXES = ['gsd-core/bin/lib/'];
 // ─── Helper functions ─────────────────────────────────────────────────────────
 
 function stripAnsi(str) {
-   
+
   return str.replace(/\x1b\[[0-9;]*m/g, '');
 }
 
+// A version string can itself contain regex metacharacters (`.`, and — via
+// prerelease/build metadata — `-`/`+`), so it must be escaped before being spliced
+// into a RegExp source, or e.g. the `.` in "1.9.0" would match ANY character.
+function escapeRegExp(str) {
+  return str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
+}
+
+// Loosely semver-shaped: leading `MAJOR.MINOR.PATCH`, optional `-prerelease` and/or
+// `+build` metadata (e.g. `1.9.0`, `1.9.0-rc.1`, `1.9.0+abc`). Deliberately loose
+// (not the full semver grammar) — this only needs to reject obviously-malformed
+// values like `'1'` (FINDING 2, #2891 review) before they reach regex construction,
+// not to be a semver validator.
+const SEMVER_ISH_RE = /^\d+\.\d+\.\d+(-[0-9A-Za-z.-]+)?(\+[0-9A-Za-z.-]+)?$/;
+
+/**
+ * Anchored, narrow version-stamp normalization — the FINDING 1 (#2891 review) fix for
+ * the prior `.split(pkgVersion).join('<VERSION>')`, which blind-replaced EVERY
+ * occurrence of the version string anywhere in emitted content. That was unsound in
+ * both directions once each side of a diff normalizes against a DIFFERENT pkgVersion
+ * (baseline vs current tree, #2891): a bare semver literal that genuinely changed
+ * between the two versions collapses to '<VERSION>' on both sides and goes invisible
+ * (false negative), while an UNCHANGED file that happens to contain a literal equal to
+ * only the CURRENT version collapses on one side only and reports as spurious drift
+ * (false positive). Emitted sources really do carry bare semver literals that are NOT
+ * install-time stamps — e.g. gsd-core/workflows/update.md's `1.4.0`/`1.3.1` examples,
+ * agents/gsd-project-researcher.md's `1.2.3`, gsd-core/workflows/help/modes/full.md's
+ * `1.0.0` — and those must stay VISIBLE to the parity gate if they ever change.
+ *
+ * So instead of replacing the version everywhere, this only normalizes it at the
+ * specific places `bin/install.js` actually stamps `pkg.version` into emitted content
+ * as a version FIELD/marker (not prose):
+ *   - `// gsd-hook-version: <ver>` / `# gsd-hook-version: <ver>` — the
+ *     `{{GSD_VERSION}}` substitution done for every emitted hook file.
+ *   - `"version": "<ver>"` — JSON manifests (plugin/extension/capability-style)
+ *     embedding the package version as a string field.
+ *   - `version: "<ver>"` / `version: <ver>` — YAML frontmatter version fields (e.g.
+ *     skill frontmatter's `yamlQuote(pkg.version)`, Hermes' category
+ *     `DESCRIPTION.md`).
+ *   - `@opengsd/gsd-core@<ver>` — pinned package-spec references.
+ *   - a file whose ENTIRE trimmed content IS the version (`gsd-core/VERSION`).
+ * Each pattern only matches when the version in the content EQUALS the supplied
+ * `pkgVersion` — this is deliberately narrow, at the cost of needing a new pattern any
+ * time the installer grows a new stamp site (see the empirical repro-harness check
+ * this fix was verified against, #2891 review FINDING 1).
+ *
+ * @param {string} content
+ * @param {string} pkgVersion - already validated non-empty semver-ish string.
+ * @returns {string}
+ */
+function normalizeVersionStamps(content, pkgVersion) {
+  const v = escapeRegExp(pkgVersion);
+  // `(?![\w.+-])` after a bare (unquoted/uncaptured-suffix) match stops a version
+  // from matching as a PREFIX of a longer version-shaped string it is not equal to
+  // (e.g. pkgVersion '1.9.0' must not match inside '1.9.0-rc.1' or '1.9.0.1').
+  return content
+    .replace(new RegExp(`((?:\\/\\/|#)\\s*gsd-hook-version:\\s*)${v}(?![\\w.+-])`, 'g'), '$1<VERSION>')
+    .replace(new RegExp(`("version"\\s*:\\s*")${v}(")`, 'g'), '$1<VERSION>$2')
+    .replace(new RegExp(`(version:\\s*")${v}(")`, 'g'), '$1<VERSION>$2')
+    .replace(new RegExp(`(version:\\s*)${v}(?![\\w.+-])`, 'g'), '$1<VERSION>')
+    .replace(new RegExp(`(@opengsd/gsd-core@)${v}(?![\\w.+-])`, 'g'), '$1<VERSION>')
+    .replace(new RegExp(`^(\\s*)${v}(\\s*)$`), '$1<VERSION>$2');
+}
+
 function walk(dir) {
   const results = [];
   for (const entry of fs.readdirSync(dir, { withFileTypes: true })) {
@@ -218,9 +288,68 @@ function walk(dir) {
  *
  * @param {string} configDir - absolute path to the installed runtime config dir
  * @param {string} root      - temp root path to replace with '<HOME>'
+ * @param {object} [opts]
+ * @param {string} [opts.pkgVersion] - the version string to normalize to '<VERSION>'.
+ *   MUST be the version of the tree that PRODUCED the emitted content at `configDir`
+ *   — NOT necessarily this checkout's own version. OMITTING this option (or the whole
+ *   `opts` argument) defaults to this checkout's own PKG_VERSION, which is only
+ *   correct when `configDir` was emitted by THIS checkout's installer. A caller
+ *   measuring a DIFFERENT tree's installer output (#2767's `repoRoot`-driven spawns)
+ *   must pass that other tree's own version explicitly, or the normalization silently
+ *   compares apples to oranges: baseline hooks baked with version X never collapse to
+ *   '<VERSION>' when normalized against version Y, so every emitted file looks changed
+ *   even when byte-identical apart from the version stamp. Must be a non-empty
+ *   semver-ish string (`MAJOR.MINOR.PATCH` with optional prerelease/build metadata)
+ *   when the key is REACHABLE at all — see the guard below for why, and why an
+ *   explicit `{ pkgVersion: undefined }` is treated as a caller error rather than
+ *   silently falling back to the default (that fallback is the exact bug being
+ *   fixed). `opts` itself must be a plain object (or omitted/undefined) — `null` or a
+ *   non-object throws rather than reaching `Object`'s coercion of `null`/`undefined`
+ *   (#2891 review FINDING 5).
  * @returns {{ [rel: string]: string }}
  */
-function buildParityManifest(configDir, root) {
+function buildParityManifest(configDir, root, opts = {}) {
+  // `opts = {}` only substitutes for an OMITTED (or explicit `undefined`) third
+  // argument — `null` and other non-object values sail past a default parameter and
+  // would otherwise reach the `in` check below and throw a raw, unhelpful
+  // `TypeError: Cannot convert undefined or null to object` (#2891 review FINDING 5).
+  // Fail with a clear, attributable message instead.
+  if (opts === null || typeof opts !== 'object' || Array.isArray(opts)) {
+    throw new Error(
+      `buildParityManifest: opts must be a plain object or omitted, got ${JSON.stringify(opts)}.`
+    );
+  }
+
+  // Distinguish "the caller didn't pass pkgVersion at all" (legitimate — use this
+  // checkout's own PKG_VERSION) from "the caller passed pkgVersion explicitly, and it
+  // happens to be undefined/null/empty/non-string" (a caller error that must throw,
+  // never silently fall back). A plain default-parameter (`{ pkgVersion = PKG_VERSION
+  // } = {}`) cannot make this distinction — JS treats an explicit `undefined` value
+  // identically to an absent key, which would let a caller-side bug (e.g. a repoRoot
+  // version lookup that resolved to undefined) silently normalize against THIS
+  // checkout's version instead of throwing — exactly the cross-tree mis-attribution
+  // bug #2891 fixes. Use the `in` operator (not `hasOwnProperty`) so the key is honored
+  // whether it is OWN or INHERITED — `Object.create({ pkgVersion: 'x' })` reaches this
+  // function with the key reachable via the prototype chain, and a caller-error value
+  // sitting there must still be validated (and rejected) rather than silently ignored
+  // in favor of the default; only a key ABSENT from the whole chain means "caller
+  // didn't specify one, use this checkout's own version" (#2891 review FINDING 4).
+  const pkgVersion = 'pkgVersion' in opts ? opts.pkgVersion : PKG_VERSION;
+
+  // GUARD: an empty/falsy/non-string/non-semver-shaped pkgVersion must never reach the
+  // normalization below. A careless caller passing e.g. '1' would silently match and
+  // corrupt content that merely contains that digit as a substring of an unrelated
+  // number (#2891 review FINDING 2) — and, pre-FINDING-1, an empty string reaching
+  // `.split('')` would have exploded manifest content into individual characters. Fail
+  // closed instead of falling back to this checkout's PKG_VERSION: a silent fallback is
+  // exactly the cross-tree mis-attribution bug this option exists to fix (#2891).
+  if (typeof pkgVersion !== 'string' || pkgVersion.length === 0 || !SEMVER_ISH_RE.test(pkgVersion)) {
+    throw new Error(
+      `buildParityManifest: pkgVersion must be a non-empty semver-ish string ` +
+      `(MAJOR.MINOR.PATCH, optional -prerelease/+build), got ${JSON.stringify(pkgVersion)}. ` +
+      'Pass the version of the tree that produced the emitted content at configDir.'
+    );
+  }
   const allFiles = walk(configDir);
   const unsorted = {};
 
@@ -246,12 +375,21 @@ function buildParityManifest(configDir, root) {
 
     const content = fs.readFileSync(full);
     // Normalize every occurrence of the temp root so hashes are stable across runs.
-    // Also normalize the package version so the golden survives `npm version` bumps
-    // (the rc release step bakes the new version into hook files before running tests).
-    const normalized = content.toString('utf8')
-      .split(realRoot).join('<HOME>')
-      .split(root).join('<HOME>')
-      .split(PKG_VERSION).join('<VERSION>');
+    // Also normalize the PRODUCING tree's package version at its known stamp sites
+    // (pkgVersion, defaulted to this checkout's own) — via the ANCHORED
+    // normalizeVersionStamps, not a blind substring replace — so the golden survives
+    // `npm version` bumps (the rc release step bakes the new version into hook files
+    // before running tests) and, for a cross-tree caller, so the version stamp baked
+    // in by a DIFFERENT tree's installer doesn't masquerade as a real content diff,
+    // WITHOUT also masking a genuine content change to an unrelated bare semver
+    // literal that happens to equal pkgVersion (#2891; see normalizeVersionStamps'
+    // own doc comment for the blind-replace failure modes this replaced).
+    const normalized = normalizeVersionStamps(
+      content.toString('utf8')
+        .split(realRoot).join('<HOME>')
+        .split(root).join('<HOME>'),
+      pkgVersion,
+    );
     const hash = crypto.createHash('sha256').update(normalized).digest('hex').slice(0, 16);
     unsorted[rel] = hash;
   }
@@ -266,7 +404,14 @@ function buildParityManifest(configDir, root) {
 
 /** Sorted list of emitted relative paths for a runtime install (file-set snapshot,
  *  #2267). Reuses buildParityManifest's exact exclusion set so the tree and the
- *  content manifest never diverge on which files they cover. */
+ *  content manifest never diverge on which files they cover. Deliberately does NOT
+ *  take (or forward) a `pkgVersion`/`opts` parameter: the emitted FILE SET is
+ *  version-independent — `pkgVersion` only ever changes which bytes a file's HASH
+ *  normalizes to, never which paths buildParityManifest walks or excludes — so there
+ *  is nothing for a caller to pass here, and forwarding one through would only let a
+ *  bad version value make a pure file-set query throw for no file-set-shaped reason
+ *  (#2891 review FINDING 6; verified no caller passes a third argument —
+ *  tests/golden-install-tree.test.cjs, scripts/gen-install-tree-fixtures.cjs). */
 function buildInstallTree(configDir, root) {
   return Object.keys(buildParityManifest(configDir, root)).sort();
 }