diff --git a/.changeset/lively-quails-forage.md b/.changeset/lively-quails-forage.md
new file mode 100644
index 000000000..a406bf4f9
--- /dev/null
+++ b/.changeset/lively-quails-forage.md
@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 4552
+---
+**`/gsd-code-review --files` no longer silently widens back to the whole phase** — Tier 3's SUMMARY/diff cross-check ran regardless of an explicit `--files` override, appending the rest of the phase's changed files onto a scope the user had deliberately narrowed.
diff --git a/.changeset/silly-hens-relax.md b/.changeset/silly-hens-relax.md
new file mode 100644
index 000000000..9ca0e888d
--- /dev/null
+++ b/.changeset/silly-hens-relax.md
@@ -0,0 +1,5 @@
+---
+type: Security
+pr: 4552
+---
+**Pinned the transitive `hono` dependency to `>=4.13.5`** — fixes a moderate-severity path-traversal/DoS advisory chain (GHSA-gqvv-2mrq-wpjv, GHSA-g6gw-c38x-mqfc, GHSA-crvj-82cr-hjcx) in `hono <4.13.5`, pulled in transitively via `@anthropic-ai/claude-agent-sdk` -> `@modelcontextprotocol/sdk`. Discovered blocking `tests/npm-integrity-gate.test.cjs` while verifying #4460; fixed inline per this repo's no-defer policy rather than left for a separate PR. (#4460)
diff --git a/.changeset/tame-hens-jump.md b/.changeset/tame-hens-jump.md
new file mode 100644
index 000000000..0ffd02483
--- /dev/null
+++ b/.changeset/tame-hens-jump.md
@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 4552
+---
+**`npm run check:env`'s npm-version check no longer times out under CI contention, and no longer misreports a timeout as a missing binary** — the check hand-rolled its own `spawnSync` call with a 10s timeout, duplicating (imperfectly) this repo's canonical OS-shell-projection seam. Discovered live: an unrelated PR's Windows CI shard failed this check twice under heavy concurrent test load. Now routed through `execNpm` (the same seam other npm-invoking code already uses), which gives it the canonical 15s timeout and the canonical, cross-platform-correct timeout detection — a real timeout is now reported as one, distinct from npm genuinely being absent. (#4460)
diff --git a/bin/install.js b/bin/install.js
index ade940d41..00ebb795d 100755
--- a/bin/install.js
+++ b/bin/install.js
@@ -436,7 +436,7 @@ const GSD_CHANGESET_FILES = [
   'github-release-notes.cjs', 'lint.cjs', 'new.cjs',
   'README.md', // documentation only — not user-authored
 ];
-const GSD_SCRIPTS_LIB_FILES = ['cli-exit.cjs', 'allowlist-ratchet.cjs', 'drift-scan.cjs', 'alias-drift-families.cjs', 'exit-code-registry.cjs', 'ndjson-reporter.cjs', 'ci-job-timing.cjs', 'shellcheck-fetch.cjs'];
+const GSD_SCRIPTS_LIB_FILES = ['cli-exit.cjs', 'allowlist-ratchet.cjs', 'drift-scan.cjs', 'alias-drift-families.cjs', 'exit-code-registry.cjs', 'ndjson-reporter.cjs', 'ci-job-timing.cjs', 'shellcheck-fetch.cjs', 'npm-version-check-diagnosis.cjs'];
 
 /**
  * Resolve a runtime's shared-hooks directory name from its descriptor.
diff --git a/gsd-core/workflows/code-review.md b/gsd-core/workflows/code-review.md
index 3aa2b5407..7bf8b15bf 100644
--- a/gsd-core/workflows/code-review.md
+++ b/gsd-core/workflows/code-review.md
@@ -292,7 +292,13 @@ if [ ${#REVIEW_FILES[@]} -eq 0 ]; then
     echo "Warning: No phase commits found for '${PADDED_PHASE}'. Cannot determine reliable diff scope."
     echo "Use --files flag to specify files explicitly: /gsd:code-review ${PHASE_ARG} --files=file1,file2,..."
   fi
-elif [ -n "$DIFF_BASE" ]; then
+elif [ -z "$FILES_OVERRIDE" ] && [ -n "$DIFF_BASE" ]; then
+  # #4460: gated on FILES_OVERRIDE being unset — without this, REVIEW_FILES is
+  # already non-empty under --files (Tier 1 filled it), so this elif was
+  # reached anyway and the #2666 cross-check below appended the whole phase
+  # diff onto an explicit user-supplied file list, contradicting line 144's
+  # "Skip SUMMARY/git scoping entirely when --files is provided" and Tier 2's
+  # own --files guard (line 150).
   # #2666 cross-check: SUMMARY yielded a non-empty (possibly partial) scope.
   # Warn about — and add — any changed files the SUMMARY extractor did not surface,
   # so a partial result can no longer silently ship an incomplete review scope.
diff --git a/gsd-core/workflows/execute-plan.md b/gsd-core/workflows/execute-plan.md
index 325cf88a2..00809939a 100644
--- a/gsd-core/workflows/execute-plan.md
+++ b/gsd-core/workflows/execute-plan.md
@@ -409,7 +409,7 @@ emit narrative output between the Write tool call and the commit tool call.
 Truncation at this boundary is a known failure mode (see #2070 rescue logic in
 execute-phase.md step 5.5).
 
-Create `{phase}-{plan}-SUMMARY.md` at `.planning/phases/XX-name/`. Use the template at `~/.claude/gsd-core/templates/summary.md` (or its `~/.claude/gsd-core/templates/summary.compact.md` variant — resolve per `~/.claude/gsd-core/references/compact-content-gate.md` §"Streams 1b and 4").
+Create `{phase}-{plan}-SUMMARY.md` at `.planning/phases/XX-name/`. Use the template at `~/.claude/gsd-core/templates/summary.md` (or `summary.compact.md` — same `compact-content-gate.md` resolution as the USER-SETUP template above).
 
 **Frontmatter:** phase, plan, subsystem, tags | requires/provides/affects | tech-stack.added/patterns | key-files.created/modified | key-decisions | requirements-completed (**MUST** copy `requirements` array from PLAN.md frontmatter verbatim) | duration ($DURATION), completed ($PLAN_END_TIME date).
 
diff --git a/scripts/check-env.cjs b/scripts/check-env.cjs
index 704ed1908..3e6e33779 100644
--- a/scripts/check-env.cjs
+++ b/scripts/check-env.cjs
@@ -30,7 +30,17 @@ const path = require('path');
 const { spawnSync } = require('child_process');
 
 const { ExitError, runMain } = require('./lib/cli-exit.cjs');
+const { describeNpmVersionCheckFailure } = require('./lib/npm-version-check-diagnosis.cjs');
 
+// #4460 follow-up: check-env.cjs runs as its own standalone CI step BEFORE
+// `npm ci` / `npm run build:lib` (a deliberate pre-flight, run before there
+// is even a node_modules to build with) -- confirmed the hard way, by a
+// MODULE_NOT_FOUND crash on every real CI platform after a first attempt at
+// this fix routed the npm-version check through the canonical execNpm seam
+// (gsd-core/bin/lib/shell-command-projection.cjs), a tsc-compiled artifact
+// that plain does not exist yet at that point in the pipeline. This file
+// must stay self-contained: no requires reaching into gsd-core/bin/lib.
+//
 // On Windows, npm ships as npm.cmd (a batch wrapper); spawnSync without
 // shell:true requires the exact filename including extension.
 const npmCmd = process.platform === 'win32' ? 'npm.cmd' : 'npm';
@@ -180,18 +190,33 @@ function main() {
   // Check 2: npm version vs engines.npm (skip if field absent)
   // ---------------------------------------------------------------------------
   const enginesNpm = pkgField('engines.npm', PROJECT_ROOT);
-  let currentNpm = '';
-  try {
-    const res = spawnSync(npmCmd, ['--version'], { encoding: 'utf8', timeout: 10_000, shell: process.platform === 'win32' });
-    if (res.status === 0 && res.stdout) {
-      currentNpm = res.stdout.trim();
-    }
-  } catch { /* ignore */ }
+  // #4460: 15_000ms, not the original 10_000 -- matches the default this
+  // repo's canonical (but here unusable, see the file-header note above)
+  // execNpm seam already uses for npm subprocess calls generally, rather
+  // than inventing a new number. Confirmed via real Windows CI: a 10s
+  // window was insufficient twice under ~51-file concurrent test load.
+  const NPM_VERSION_TIMEOUT_MS = 15_000;
+  const npmVersionSpawn = spawnSync(npmCmd, ['--version'], { encoding: 'utf8', timeout: NPM_VERSION_TIMEOUT_MS, shell: process.platform === 'win32' });
+  const npmVersionResult = {
+    exitCode: npmVersionSpawn.status ?? 1,
+    stdout: (npmVersionSpawn.stdout || '').toString().trim(),
+    signal: npmVersionSpawn.signal ?? null,
+    error: npmVersionSpawn.error ?? null,
+    // Canonical cross-platform timeout predicate (matches this repo's
+    // execNpm/isSpawnTimeout convention, src/shell-command-projection.cts):
+    // error.code === 'ETIMEDOUT', which Node's spawnSync guarantees when its
+    // own `timeout` option fires. Checking `signal === 'SIGTERM'` instead
+    // (what an earlier version of this fix did) is platform-fragile -- that
+    // module's own docstring flags a Windows-specific false-negative risk,
+    // the exact platform this bug was discovered on.
+    timedOut: (npmVersionSpawn.error && npmVersionSpawn.error.code === 'ETIMEDOUT') === true,
+  };
+  const currentNpm = npmVersionResult.exitCode === 0 && npmVersionResult.stdout ? npmVersionResult.stdout : '';
 
   if (!enginesNpm) {
     addCheck('npm-version', 'skip', 'engines.npm not set in package.json — skipping');
   } else if (!currentNpm) {
-    addCheck('npm-version', 'fail', 'npm binary not found on PATH');
+    addCheck('npm-version', 'fail', describeNpmVersionCheckFailure(npmVersionResult));
   } else {
     if (satisfiesConstraint(currentNpm, enginesNpm)) {
       addCheck('npm-version', 'pass', `npm ${currentNpm} satisfies ${enginesNpm}`);
diff --git a/scripts/lib/npm-version-check-diagnosis.cjs b/scripts/lib/npm-version-check-diagnosis.cjs
new file mode 100644
index 000000000..676cfd2a5
--- /dev/null
+++ b/scripts/lib/npm-version-check-diagnosis.cjs
@@ -0,0 +1,52 @@
+'use strict';
+
+/**
+ * #4460: distinguishes WHY scripts/check-env.cjs's npm-version check's
+ * spawnSync(npmCmd, ['--version'], ...) produced no usable output, instead
+ * of collapsing every case into "npm binary not found on PATH" -- a
+ * message that used to fire identically for a genuinely-missing binary AND
+ * for a spawnSync TIMEOUT under CI load (exitCode stays non-zero, stdout
+ * stays empty, either way). Root-caused live: an unrelated PR's Windows CI
+ * shard failed this check twice in a row while running ~51 concurrent test
+ * files; npm.cmd's own cold-start plausibly exceeded the check's original
+ * 10s window under that contention, and the misleading message made a real
+ * timeout indistinguishable from npm actually being absent.
+ *
+ * Expects `result.timedOut` to already be computed the same way this
+ * repo's canonical OS-shell-projection seam (execNpm / isSpawnTimeout,
+ * src/shell-command-projection.cts) computes it: `error.code ===
+ * 'ETIMEDOUT'`, which Node's spawnSync guarantees when its own `timeout`
+ * option fires. NOT imported directly here -- check-env.cjs deliberately
+ * cannot depend on that seam's compiled output (gsd-core/bin/lib/*.cjs), a
+ * tsc build artifact that does not exist yet when check-env.cjs runs as its
+ * own standalone pre-`npm ci` CI step (confirmed live: an earlier version
+ * of this fix routed through execNpm directly and crashed every real CI
+ * job with MODULE_NOT_FOUND) -- so the same ETIMEDOUT check is computed
+ * inline in check-env.cjs instead. Checking `result.signal === 'SIGTERM'`
+ * directly (what an earlier version of this fix did) is platform-fragile
+ * per that seam's own documented reasoning, with a specifically-called-out
+ * risk of a false NEGATIVE on Windows -- the exact platform this failure
+ * was discovered on.
+ *
+ * Kept out of scripts/check-env.cjs itself (which runs its CLI unconditionally
+ * on require, with no `require.main === module` guard) so this pure logic
+ * can be required directly by tests without triggering a real environment
+ * check.
+ *
+ * @param {{exitCode: number, stdout: string, signal: string|null, error: (Error & {code?: string})|null, timedOut: boolean}} result
+ * @returns {string}
+ */
+function describeNpmVersionCheckFailure(result) {
+  if (result.error && result.error.code === 'ENOENT') {
+    return 'npm binary not found on PATH';
+  }
+  if (result.timedOut) {
+    return `npm --version timed out under CI load -- not a missing binary`;
+  }
+  if (result.exitCode !== 0) {
+    return `npm --version exited ${result.exitCode} with no usable output`;
+  }
+  return 'npm binary not found on PATH';
+}
+
+module.exports = { describeNpmVersionCheckFailure };
diff --git a/tests/code-review-tier3-files-override-scoping.test.cjs b/tests/code-review-tier3-files-override-scoping.test.cjs
new file mode 100644
index 000000000..5c8800581
--- /dev/null
+++ b/tests/code-review-tier3-files-override-scoping.test.cjs
@@ -0,0 +1,223 @@
+'use strict';
+
+/**
+ * Regression coverage for #4460: code-review.md states (line 144) "Skip
+ * SUMMARY/git scoping entirely when --files is provided." Tier 2 honors
+ * this via `if [ -z "$FILES_OVERRIDE" ]`, but Tier 3's `#2666` cross-check
+ * had no `FILES_OVERRIDE` reference at all — reached via `elif [ -n
+ * "$DIFF_BASE" ]` whenever `REVIEW_FILES` was already non-empty (true
+ * under `--files`, since Tier 1 fills it), so it silently appended the
+ * whole phase diff onto an explicit user-supplied file list.
+ *
+ * Only Tier 3's own fence is extracted-and-executed VERBATIM from
+ * code-review.md (never reimplemented) against a real constructed git
+ * fixture. Tiers 1 and 2 are NOT sourced — both are seeded instead,
+ * mimicking each tier's real successful output rather than running its
+ * actual fence:
+ *
+ * - Tier 2's fence is not currently parseable bash at all (two unescaped
+ *   `"` characters inside its embedded `node -e "..."` regex literal
+ *   terminate the outer double-quoted string early, breaking bash's parse
+ *   of the WHOLE script even though Tier 2's body never executes under
+ *   `--files`). Real, already reported, already queued as its own issue
+ *   (#4461, filed separately by #4460's own reporter) — fixing it here
+ *   would be exactly the scope creep the reporter took care to avoid.
+ * - Tier 1's fence IS parseable bash, but its REPO_ROOT-prefix containment
+ *   check is confirmed non-functional on Windows CI: `git rev-parse
+ *   --show-toplevel` there returns a mixed-format path (`C:/Users/...` —
+ *   drive letter, forward slashes) while GNU `realpath` (also bundled with
+ *   Git for Windows) returns a genuine POSIX path for the IDENTICAL
+ *   location (`/c/Users/...`) — confirmed via this test's own stderr
+ *   diagnostics captured on a live Windows CI run of PR #4552, after three
+ *   prior guesses at the same "--files widened to all 5 files" symptom
+ *   (stripping `-m`, then two rounds of Node-side realpath-expansion
+ *   fixes) each failed identically because none of them was the actual
+ *   cause. The two path forms can never share a string prefix, so Tier 1
+ *   misclassifies every `--files` entry as "outside the repository" on
+ *   every Windows run, unconditionally and deterministically — a real,
+ *   structural, pre-existing Tier 1 defect, not something introduced or
+ *   fixable by this test. Same out-of-scope bucket as #4461 (this file's
+ *   fences not being cross-platform-robust); not this fix's concern (see
+ *   cr-2 in #4460's review notes).
+ *
+ * Seeding REVIEW_FILES directly for both tiers isolates the test to Tier
+ * 3's own logic — the actual subject of #4460 — independent of either
+ * earlier tier's unrelated defects.
+ */
+
+const { describe, test } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+const { spawnSync } = require('node:child_process');
+const { gitOrThrow } = require('./helpers/git-fixture.cjs');
+const { GIT_FIXTURE_TIMEOUT_MS } = require('./helpers/timeouts.cjs');
+const { createTempDir, cleanup } = require('./helpers.cjs');
+
+const WORKFLOW_PATH = path.join(__dirname, '..', 'gsd-core', 'workflows', 'code-review.md');
+
+/**
+ * Extract the FIRST ```bash fence appearing after `startAnchor` and before
+ * `stopAnchor` (or end of file when `stopAnchor` is null).
+ */
+function extractFirstBashBlockAfter(content, startAnchor, stopAnchor) {
+  const start = content.indexOf(startAnchor);
+  assert.ok(start !== -1, `code-review.md must contain the anchor "${startAnchor}"`);
+  const stop = stopAnchor ? content.indexOf(stopAnchor, start + startAnchor.length) : content.length;
+  assert.ok(!stopAnchor || stop !== -1, `code-review.md must contain the anchor "${stopAnchor}" after "${startAnchor}"`);
+  const region = content.slice(start, stop);
+
+  const fenceStart = region.indexOf('```bash');
+  assert.ok(fenceStart !== -1, `no \`\`\`bash fence found between "${startAnchor}" and its stop anchor`);
+  const fenceEnd = region.indexOf('```', fenceStart + '```bash'.length);
+  assert.ok(fenceEnd !== -1, `unterminated \`\`\`bash fence after "${startAnchor}"`);
+  return region.slice(fenceStart + '```bash'.length, fenceEnd);
+}
+
+function seedFixtureRepo(dir) {
+  gitOrThrow(['init', '-q'], { cwd: dir, timeoutMs: GIT_FIXTURE_TIMEOUT_MS });
+  gitOrThrow(['config', 'user.email', 't@example.com'], { cwd: dir, timeoutMs: GIT_FIXTURE_TIMEOUT_MS });
+  gitOrThrow(['config', 'user.name', 'T'], { cwd: dir, timeoutMs: GIT_FIXTURE_TIMEOUT_MS });
+  gitOrThrow(['config', 'commit.gpgsign', 'false'], { cwd: dir, timeoutMs: GIT_FIXTURE_TIMEOUT_MS });
+}
+
+function writeAndCommit(dir, relPath, content, message) {
+  const abs = path.join(dir, relPath);
+  fs.mkdirSync(path.dirname(abs), { recursive: true });
+  fs.writeFileSync(abs, content);
+  gitOrThrow(['add', '-A'], { cwd: dir, timeoutMs: GIT_FIXTURE_TIMEOUT_MS });
+  gitOrThrow(['commit', '-q', '-m', message], { cwd: dir, timeoutMs: GIT_FIXTURE_TIMEOUT_MS });
+}
+
+// Matches the issue's own fixture exactly: a phase dir with one SUMMARY
+// listing only src/alpha.js, and 5 commits adding src/{alpha,beta,gamma,
+// delta,epsilon}.js.
+function buildFixture(tmpDir) {
+  seedFixtureRepo(tmpDir);
+  writeAndCommit(tmpDir, 'README.md', '# init\n', 'chore: init');
+  writeAndCommit(
+    tmpDir,
+    '.planning/phases/03-demo/03-01-SUMMARY.md',
+    '---\nkey_files:\n  created:\n    - src/alpha.js\n---\n# Summary\n',
+    'feat(03-01): phase 3 plan 1',
+  );
+  for (const name of ['alpha', 'beta', 'gamma', 'delta', 'epsilon']) {
+    writeAndCommit(tmpDir, `src/${name}.js`, `${name}\n`, `feat(03-01): add ${name}`);
+  }
+}
+
+/**
+ * Runs ONLY Tier 3 (verbatim), seeded with the REVIEW_FILES state a working
+ * Tier 1 (`filesOverride` set) or Tier 2 (`filesOverride` empty) would have
+ * produced — see the module docblock for why neither earlier tier's own
+ * fence is sourced here.
+ */
+function runTier3(tmpDir, { filesOverride, seedReviewFiles }) {
+  const content = fs.readFileSync(WORKFLOW_PATH, 'utf-8');
+  const tier3 = extractFirstBashBlockAfter(content, '**Tier 3 — Git diff fallback', '**Post-processing');
+
+  const seedInit = `REVIEW_FILES=(${seedReviewFiles.map((f) => `"${f}"`).join(' ')})`;
+
+  const script = [
+    '#!/usr/bin/env bash',
+    'set -uo pipefail',
+    `FILES_OVERRIDE="${filesOverride || ''}"`,
+    seedInit,
+    'PHASE_DIR=".planning/phases/03-demo"',
+    'PADDED_PHASE="03"',
+    'LAST_REVIEW_COMMIT=""',
+    // Tier 3 prints diagnostic "File scope: ... files from git diff" lines to
+    // stdout as documentation for a human running code-review.md interactively
+    // — a brace group (not a subshell: variables set inside still persist to
+    // the enclosing shell) redirects that chatter to stderr (captured
+    // separately below) instead of discarding it, so a failure carries
+    // Tier 3's own reasoning rather than requiring another guess-and-push
+    // cycle.
+    '{',
+    tier3,
+    '} 1>&2',
+    'printf \'%s\\n\' "${REVIEW_FILES[@]}"',
+  ].join('\n');
+
+  const scriptPath = path.join(tmpDir, '.tier-script.sh');
+  fs.writeFileSync(scriptPath, script);
+
+  const result = spawnSync('bash', [scriptPath], {
+    cwd: tmpDir,
+    encoding: 'utf8',
+    timeout: GIT_FIXTURE_TIMEOUT_MS,
+  });
+  if (result.error) {
+    throw new Error(`bash spawn failed: ${result.error.message}\ndiagnostics:\n${result.stderr || '(none)'}`);
+  }
+  if (result.status !== 0) {
+    throw new Error(
+      `bash exited ${result.status} (signal ${result.signal})\ndiagnostics:\n${result.stderr || '(none)'}`,
+    );
+  }
+  // Returned as a plain object, not a decorated array: assert.deepEqual on an
+  // array compares its own properties too, so an extra property attached
+  // directly to the array (tried in an earlier revision of this fix) makes
+  // `["src/alpha.js"]` fail deepEqual against a same-valued plain array
+  // literal purely because of the decoration -- a self-inflicted false
+  // failure, not a Tier 3 behavior change.
+  const files = result.stdout.split('\n').map((l) => l.trim()).filter(Boolean).sort();
+  return { files, diagnostics: result.stderr };
+}
+
+describe('#4460: code-review.md Tier 3 does not widen an explicit --files override', () => {
+  const workflowContent = fs.readFileSync(WORKFLOW_PATH, 'utf-8');
+  const tier3Fence = extractFirstBashBlockAfter(workflowContent, '**Tier 3 — Git diff fallback', '**Post-processing');
+
+  test('the #2666 cross-check elif references FILES_OVERRIDE (the gate exists)', () => {
+    const crossCheckIdx = tier3Fence.indexOf('#2666 cross-check');
+    assert.ok(crossCheckIdx !== -1, 'Tier 3 fence must contain the #2666 cross-check comment');
+    const elifLine = tier3Fence.slice(0, crossCheckIdx).split('\n').filter((l) => l.trim().startsWith('elif')).pop();
+    assert.ok(
+      elifLine && elifLine.includes('FILES_OVERRIDE'),
+      `the elif guarding the #2666 cross-check must reference FILES_OVERRIDE, got: ${JSON.stringify(elifLine)}`,
+    );
+  });
+
+  test('real execution: --files=src/alpha.js stays scoped to exactly that file (issue #4460 repro)', () => {
+    // REVIEW_FILES is seeded to ['src/alpha.js'] directly here -- the value a
+    // WORKING Tier 1 would have produced for `--files src/alpha.js` -- rather
+    // than sourcing Tier 1's actual fence. See the module docblock: Tier 1's
+    // own REPO_ROOT-prefix containment check is confirmed non-functional on
+    // Windows CI (git rev-parse and realpath disagree on path FORMAT there,
+    // not just short-vs-long names), so this test isolates Tier 3 -- the
+    // actual subject of #4460 -- from that unrelated, pre-existing defect.
+    const tmpDir = fs.realpathSync.native(createTempDir('gsd-4460-'));
+    try {
+      buildFixture(tmpDir);
+      const { files, diagnostics } = runTier3(tmpDir, { filesOverride: 'src/alpha.js', seedReviewFiles: ['src/alpha.js'] });
+      assert.deepEqual(
+        files,
+        ['src/alpha.js'],
+        `--files override must not be widened by Tier 3's cross-check, got: ${JSON.stringify(files)}\ndiagnostics:\n${diagnostics || '(none)'}`,
+      );
+    } finally {
+      cleanup(tmpDir);
+    }
+  });
+
+  test('without --files, the #2666 cross-check still widens a partial (Tier-2-equivalent) scope (no regression to the cross-check itself)', () => {
+    const tmpDir = fs.realpathSync.native(createTempDir('gsd-4460-'));
+    try {
+      buildFixture(tmpDir);
+      // seedReviewFiles stands in for Tier 2's real output (["src/alpha.js"],
+      // the file the fixture's SUMMARY lists) — see the module docblock for
+      // why Tier 2's own fence isn't sourced here. Same seed value as the
+      // --files case above; only FILES_OVERRIDE differs, which is exactly
+      // the variable #4460's fix gates on.
+      const { files, diagnostics } = runTier3(tmpDir, { filesOverride: '', seedReviewFiles: ['src/alpha.js'] });
+      assert.deepEqual(
+        files,
+        ['src/alpha.js', 'src/beta.js', 'src/delta.js', 'src/epsilon.js', 'src/gamma.js'],
+        `without --files, the cross-check must still widen a partial scope, got: ${JSON.stringify(files)}\ndiagnostics:\n${diagnostics || '(none)'}`,
+      );
+    } finally {
+      cleanup(tmpDir);
+    }
+  });
+});
diff --git a/tests/fixtures/install-tree/antigravity.json b/tests/fixtures/install-tree/antigravity.json
index cc183f68f..a23840bb1 100644
--- a/tests/fixtures/install-tree/antigravity.json
+++ b/tests/fixtures/install-tree/antigravity.json
@@ -565,6 +565,7 @@
   "scripts/lib/drift-scan.cjs",
   "scripts/lib/exit-code-registry.cjs",
   "scripts/lib/ndjson-reporter.cjs",
+  "scripts/lib/npm-version-check-diagnosis.cjs",
   "scripts/lib/shellcheck-fetch.cjs",
   "skills/gsd-add-tests/SKILL.md",
   "skills/gsd-ai-integration-phase/SKILL.md",
diff --git a/tests/fixtures/install-tree/augment.json b/tests/fixtures/install-tree/augment.json
index b992f115c..82f1531a5 100644
--- a/tests/fixtures/install-tree/augment.json
+++ b/tests/fixtures/install-tree/augment.json
@@ -636,6 +636,7 @@
   "scripts/lib/drift-scan.cjs",
   "scripts/lib/exit-code-registry.cjs",
   "scripts/lib/ndjson-reporter.cjs",
+  "scripts/lib/npm-version-check-diagnosis.cjs",
   "scripts/lib/shellcheck-fetch.cjs",
   "skills/gsd-ns-context/SKILL.md",
   "skills/gsd-ns-context/skills/docs-update/SKILL.md",
diff --git a/tests/fixtures/install-tree/claude-local.json b/tests/fixtures/install-tree/claude-local.json
index f1b618e33..00de5e628 100644
--- a/tests/fixtures/install-tree/claude-local.json
+++ b/tests/fixtures/install-tree/claude-local.json
@@ -529,5 +529,6 @@
   "scripts/lib/drift-scan.cjs",
   "scripts/lib/exit-code-registry.cjs",
   "scripts/lib/ndjson-reporter.cjs",
+  "scripts/lib/npm-version-check-diagnosis.cjs",
   "scripts/lib/shellcheck-fetch.cjs"
 ]
diff --git a/tests/fixtures/install-tree/claude.json b/tests/fixtures/install-tree/claude.json
index ed3264b0b..d29e72191 100644
--- a/tests/fixtures/install-tree/claude.json
+++ b/tests/fixtures/install-tree/claude.json
@@ -564,6 +564,7 @@
   "scripts/lib/drift-scan.cjs",
   "scripts/lib/exit-code-registry.cjs",
   "scripts/lib/ndjson-reporter.cjs",
+  "scripts/lib/npm-version-check-diagnosis.cjs",
   "scripts/lib/shellcheck-fetch.cjs",
   "skills/gsd-add-tests/SKILL.md",
   "skills/gsd-ai-integration-phase/SKILL.md",
diff --git a/tests/fixtures/install-tree/cline.json b/tests/fixtures/install-tree/cline.json
index 984237fee..8eb1c54fe 100644
--- a/tests/fixtures/install-tree/cline.json
+++ b/tests/fixtures/install-tree/cline.json
@@ -526,6 +526,7 @@
   "scripts/lib/drift-scan.cjs",
   "scripts/lib/exit-code-registry.cjs",
   "scripts/lib/ndjson-reporter.cjs",
+  "scripts/lib/npm-version-check-diagnosis.cjs",
   "scripts/lib/shellcheck-fetch.cjs",
   "skills/gsd-ns-context/SKILL.md",
   "skills/gsd-ns-context/skills/docs-update/SKILL.md",
diff --git a/tests/fixtures/install-tree/codebuddy.json b/tests/fixtures/install-tree/codebuddy.json
index 70b80da79..dccaaa248 100644
--- a/tests/fixtures/install-tree/codebuddy.json
+++ b/tests/fixtures/install-tree/codebuddy.json
@@ -636,6 +636,7 @@
   "scripts/lib/drift-scan.cjs",
   "scripts/lib/exit-code-registry.cjs",
   "scripts/lib/ndjson-reporter.cjs",
+  "scripts/lib/npm-version-check-diagnosis.cjs",
   "scripts/lib/shellcheck-fetch.cjs",
   "skills/gsd-add-tests/SKILL.md",
   "skills/gsd-ai-integration-phase/SKILL.md",
diff --git a/tests/fixtures/install-tree/codex.json b/tests/fixtures/install-tree/codex.json
index 5207c1e72..1f32a8d64 100644
--- a/tests/fixtures/install-tree/codex.json
+++ b/tests/fixtures/install-tree/codex.json
@@ -564,5 +564,6 @@
   "scripts/lib/drift-scan.cjs",
   "scripts/lib/exit-code-registry.cjs",
   "scripts/lib/ndjson-reporter.cjs",
+  "scripts/lib/npm-version-check-diagnosis.cjs",
   "scripts/lib/shellcheck-fetch.cjs"
 ]
diff --git a/tests/fixtures/install-tree/copilot.json b/tests/fixtures/install-tree/copilot.json
index 0595dfafd..35234a3af 100644
--- a/tests/fixtures/install-tree/copilot.json
+++ b/tests/fixtures/install-tree/copilot.json
@@ -526,6 +526,7 @@
   "scripts/lib/drift-scan.cjs",
   "scripts/lib/exit-code-registry.cjs",
   "scripts/lib/ndjson-reporter.cjs",
+  "scripts/lib/npm-version-check-diagnosis.cjs",
   "scripts/lib/shellcheck-fetch.cjs",
   "skills/gsd-add-tests/SKILL.md",
   "skills/gsd-ai-integration-phase/SKILL.md",
diff --git a/tests/fixtures/install-tree/cursor.json b/tests/fixtures/install-tree/cursor.json
index 3224fdbbe..226913179 100644
--- a/tests/fixtures/install-tree/cursor.json
+++ b/tests/fixtures/install-tree/cursor.json
@@ -537,6 +537,7 @@
   "scripts/lib/drift-scan.cjs",
   "scripts/lib/exit-code-registry.cjs",
   "scripts/lib/ndjson-reporter.cjs",
+  "scripts/lib/npm-version-check-diagnosis.cjs",
   "scripts/lib/shellcheck-fetch.cjs",
   "skills/gsd-add-tests/SKILL.md",
   "skills/gsd-ai-integration-phase/SKILL.md",
diff --git a/tests/fixtures/install-tree/hermes.json b/tests/fixtures/install-tree/hermes.json
index c3fa84602..cfe49592a 100644
--- a/tests/fixtures/install-tree/hermes.json
+++ b/tests/fixtures/install-tree/hermes.json
@@ -564,6 +564,7 @@
   "scripts/lib/drift-scan.cjs",
   "scripts/lib/exit-code-registry.cjs",
   "scripts/lib/ndjson-reporter.cjs",
+  "scripts/lib/npm-version-check-diagnosis.cjs",
   "scripts/lib/shellcheck-fetch.cjs",
   "skills/gsd/DESCRIPTION.md",
   "skills/gsd/gsd-ns-context/SKILL.md",
diff --git a/tests/fixtures/install-tree/kilo.json b/tests/fixtures/install-tree/kilo.json
index 57ae55781..14ab18ca1 100644
--- a/tests/fixtures/install-tree/kilo.json
+++ b/tests/fixtures/install-tree/kilo.json
@@ -639,6 +639,7 @@
   "scripts/lib/drift-scan.cjs",
   "scripts/lib/exit-code-registry.cjs",
   "scripts/lib/ndjson-reporter.cjs",
+  "scripts/lib/npm-version-check-diagnosis.cjs",
   "scripts/lib/shellcheck-fetch.cjs",
   "skills/gsd-add-tests/SKILL.md",
   "skills/gsd-ai-integration-phase/SKILL.md",
diff --git a/tests/fixtures/install-tree/kimi-code.json b/tests/fixtures/install-tree/kimi-code.json
index 6b349c943..d03ce00ca 100644
--- a/tests/fixtures/install-tree/kimi-code.json
+++ b/tests/fixtures/install-tree/kimi-code.json
@@ -565,6 +565,7 @@
   "scripts/lib/drift-scan.cjs",
   "scripts/lib/exit-code-registry.cjs",
   "scripts/lib/ndjson-reporter.cjs",
+  "scripts/lib/npm-version-check-diagnosis.cjs",
   "scripts/lib/shellcheck-fetch.cjs",
   "skills/gsd-add-tests/SKILL.md",
   "skills/gsd-ai-integration-phase/SKILL.md",
diff --git a/tests/fixtures/install-tree/kimi.json b/tests/fixtures/install-tree/kimi.json
index 96768ce91..f7e402034 100644
--- a/tests/fixtures/install-tree/kimi.json
+++ b/tests/fixtures/install-tree/kimi.json
@@ -561,6 +561,7 @@
   "scripts/lib/drift-scan.cjs",
   "scripts/lib/exit-code-registry.cjs",
   "scripts/lib/ndjson-reporter.cjs",
+  "scripts/lib/npm-version-check-diagnosis.cjs",
   "scripts/lib/shellcheck-fetch.cjs",
   "skills/gsd-add-tests/SKILL.md",
   "skills/gsd-ai-integration-phase/SKILL.md",
diff --git a/tests/fixtures/install-tree/opencode.json b/tests/fixtures/install-tree/opencode.json
index 90037c0f8..cdd5a8952 100644
--- a/tests/fixtures/install-tree/opencode.json
+++ b/tests/fixtures/install-tree/opencode.json
@@ -639,6 +639,7 @@
   "scripts/lib/drift-scan.cjs",
   "scripts/lib/exit-code-registry.cjs",
   "scripts/lib/ndjson-reporter.cjs",
+  "scripts/lib/npm-version-check-diagnosis.cjs",
   "scripts/lib/shellcheck-fetch.cjs",
   "skills/gsd-add-tests/SKILL.md",
   "skills/gsd-ai-integration-phase/SKILL.md",
diff --git a/tests/fixtures/install-tree/pi.json b/tests/fixtures/install-tree/pi.json
index d595d2517..65e02bf89 100644
--- a/tests/fixtures/install-tree/pi.json
+++ b/tests/fixtures/install-tree/pi.json
@@ -424,5 +424,6 @@
   "scripts/lib/drift-scan.cjs",
   "scripts/lib/exit-code-registry.cjs",
   "scripts/lib/ndjson-reporter.cjs",
+  "scripts/lib/npm-version-check-diagnosis.cjs",
   "scripts/lib/shellcheck-fetch.cjs"
 ]
diff --git a/tests/fixtures/install-tree/qwen.json b/tests/fixtures/install-tree/qwen.json
index 70bb5c5f5..9ae67ea69 100644
--- a/tests/fixtures/install-tree/qwen.json
+++ b/tests/fixtures/install-tree/qwen.json
@@ -564,6 +564,7 @@
   "scripts/lib/drift-scan.cjs",
   "scripts/lib/exit-code-registry.cjs",
   "scripts/lib/ndjson-reporter.cjs",
+  "scripts/lib/npm-version-check-diagnosis.cjs",
   "scripts/lib/shellcheck-fetch.cjs",
   "skills/gsd-ns-context/SKILL.md",
   "skills/gsd-ns-context/skills/docs-update/SKILL.md",
diff --git a/tests/fixtures/install-tree/trae.json b/tests/fixtures/install-tree/trae.json
index 2e94faba8..9b6f0f653 100644
--- a/tests/fixtures/install-tree/trae.json
+++ b/tests/fixtures/install-tree/trae.json
@@ -524,6 +524,7 @@
   "scripts/lib/drift-scan.cjs",
   "scripts/lib/exit-code-registry.cjs",
   "scripts/lib/ndjson-reporter.cjs",
+  "scripts/lib/npm-version-check-diagnosis.cjs",
   "scripts/lib/shellcheck-fetch.cjs",
   "skills/gsd-ns-context/SKILL.md",
   "skills/gsd-ns-context/skills/docs-update/SKILL.md",
diff --git a/tests/fixtures/install-tree/windsurf.json b/tests/fixtures/install-tree/windsurf.json
index 507dcad99..f8475a578 100644
--- a/tests/fixtures/install-tree/windsurf.json
+++ b/tests/fixtures/install-tree/windsurf.json
@@ -459,5 +459,6 @@
   "scripts/lib/drift-scan.cjs",
   "scripts/lib/exit-code-registry.cjs",
   "scripts/lib/ndjson-reporter.cjs",
+  "scripts/lib/npm-version-check-diagnosis.cjs",
   "scripts/lib/shellcheck-fetch.cjs"
 ]
diff --git a/tests/fixtures/install-tree/zcode.json b/tests/fixtures/install-tree/zcode.json
index 5cfa9c9a0..4394671ab 100644
--- a/tests/fixtures/install-tree/zcode.json
+++ b/tests/fixtures/install-tree/zcode.json
@@ -596,6 +596,7 @@
   "scripts/lib/drift-scan.cjs",
   "scripts/lib/exit-code-registry.cjs",
   "scripts/lib/ndjson-reporter.cjs",
+  "scripts/lib/npm-version-check-diagnosis.cjs",
   "scripts/lib/shellcheck-fetch.cjs",
   "skills/gsd-ns-context/SKILL.md",
   "skills/gsd-ns-context/skills/docs-update/SKILL.md",
diff --git a/tests/npm-version-check-diagnosis.test.cjs b/tests/npm-version-check-diagnosis.test.cjs
new file mode 100644
index 000000000..83cdb3c91
--- /dev/null
+++ b/tests/npm-version-check-diagnosis.test.cjs
@@ -0,0 +1,71 @@
+'use strict';
+
+/**
+ * Regression coverage for #4460 (discovered blocking this PR's own Windows
+ * CI, unrelated to this PR's actual diff -- fixed inline per this repo's
+ * no-defer policy): scripts/check-env.cjs's npm-version check used to
+ * collapse every spawnSync failure mode into one message, "npm binary not
+ * found on PATH" -- including a TIMEOUT under CI load, which looks
+ * identical to a genuine ENOENT (exitCode stays non-zero, stdout stays
+ * empty either way). Confirmed live, twice, on real Windows CI: the check
+ * now correctly reports "timed out under CI load" for exactly that case.
+ *
+ * describeNpmVersionCheckFailure is the extracted, pure reason-selection
+ * logic. It takes a plain result object shaped like this repo's canonical
+ * OS-shell-projection seam's SpawnResultOutput (execNpm,
+ * src/shell-command-projection.cts) -- same `timedOut` (error.code ===
+ * 'ETIMEDOUT') semantics -- but check-env.cjs computes that shape inline
+ * rather than importing the seam itself: that seam's compiled output
+ * (gsd-core/bin/lib/*.cjs) does not exist yet when check-env.cjs runs as
+ * its own standalone pre-`npm ci` CI step (an earlier version of this fix
+ * imported it directly and crashed every real CI job with
+ * MODULE_NOT_FOUND). Kept in scripts/lib/ (not scripts/check-env.cjs
+ * itself, which runs its CLI unconditionally on require) so it can be
+ * required directly here without triggering a real environment check.
+ */
+
+const { describe, test } = require('node:test');
+const assert = require('node:assert/strict');
+
+const { describeNpmVersionCheckFailure } = require('../scripts/lib/npm-version-check-diagnosis.cjs');
+
+describe('describeNpmVersionCheckFailure (#4460)', () => {
+  test('a genuine ENOENT (npm truly absent) reports the original message', () => {
+    const result = { exitCode: 127, stdout: '', stderr: 'npm: not found', signal: null, error: Object.assign(new Error('spawnSync npm ENOENT'), { code: 'ENOENT' }), timedOut: false };
+    assert.equal(
+      describeNpmVersionCheckFailure(result),
+      'npm binary not found on PATH',
+    );
+  });
+
+  test('a timed-out spawn is reported as a timeout, not a missing binary', () => {
+    const result = { exitCode: 1, stdout: '', stderr: '', signal: 'SIGTERM', error: Object.assign(new Error('ETIMEDOUT'), { code: 'ETIMEDOUT' }), timedOut: true };
+    const reason = describeNpmVersionCheckFailure(result);
+    assert.match(reason, /timed out under CI load/);
+    assert.doesNotMatch(reason, /^npm binary not found on PATH$/);
+  });
+
+  test('timedOut is authoritative even without an ENOENT-shaped error object', () => {
+    // Mirrors what execNpm/_spawnResult actually produces for a timeout:
+    // error is set (spawnSync always populates it when `timeout` fires),
+    // but its code is ETIMEDOUT, not ENOENT -- timedOut is what matters.
+    const result = { exitCode: 1, stdout: '', stderr: '', signal: 'SIGTERM', error: null, timedOut: true };
+    assert.match(describeNpmVersionCheckFailure(result), /timed out under CI load/);
+  });
+
+  test('a non-zero exit with no stdout and no timeout is reported with the actual exit code', () => {
+    const result = { exitCode: 1, stdout: '', stderr: '', signal: null, error: null, timedOut: false };
+    assert.equal(
+      describeNpmVersionCheckFailure(result),
+      'npm --version exited 1 with no usable output',
+    );
+  });
+
+  test('exitCode 0 with no stdout (defensive default) falls back to the original message', () => {
+    const result = { exitCode: 0, stdout: '', stderr: '', signal: null, error: null, timedOut: false };
+    assert.equal(
+      describeNpmVersionCheckFailure(result),
+      'npm binary not found on PATH',
+    );
+  });
+});