test(W7h): retire spec-template-sync as a duplicate of the freshness check

W7h retirement (t05 F18; Eng factual correction: the file takes 145 ms, its
"2 minutes" was the 120 s timeout, so this is a duplicate-only retirement).
Removes its scripts/free-test-durations.json entry.

Retirement card:
- test: test/spec-template-sync.test.ts (regenerate /spec into an out-dir and
  compare spec/SKILL.md + spec/sections/gate-and-file.md with the tracked
  bytes; check the generated header).
- detects: /spec template edited without regeneration, or a hand-edited
  generated file.
- non_test_callers: none.
- search_command: grep -rn spec-template-sync package.json scripts test .github
- stronger_proof / replacement: gen-skill-docs.test.ts 'generated files are
  fresh (match --dry-run)' (FRESH for every skill, no STALE anywhere; the
  dry-run covers carved sections such as spec/sections/gate-and-file.md); the
  generated-banner checks in the same file cover the header.
- history: c118e24 / 410b492 / 394db32 / b1485d8 (codex T8).
- validation: bun test test/gen-skill-docs.test.ts.

Control (scratch worktree, run against the replacement): a stale
spec/sections/gate-and-file.md, a stale spec/SKILL.md, and a spec template
edit without regeneration each fail gen-skill-docs 'generated files are fresh'
(3/3). Log: .context/mutation-spec-template-sync.md.

scripts/free-test-durations.json

@@ -867,7 +867,6 @@
     "test/spawnsync-timeout-tripwire.test.ts": 163,
     "test/spec-quality-gate-secret-sink.test.ts": 1048,
     "test/spec-template-invariants.test.ts": 23,
-    "test/spec-template-sync.test.ts": 145,
     "test/static-no-legacy-writes.test.ts": 1195,
     "test/strict-output-capture.test.ts": 89,
     "test/strict-output-formats.test.ts": 899,

test/spec-template-sync.test.ts

@@ -1,74 +0,0 @@
-/**
- * spec-template-sync: verify /spec templates ↔ generated docs stay in sync.
- *
- * Per codex T8 / eng plan: regen and assert no drift. Catches commits that
- * edit a template but forget to run `bun run gen:skill-docs`, or vice versa.
- *
- * /spec is carved (skeleton + sections/gate-and-file.md), so BOTH generated
- * artifacts are checked: a stale section is the same drift bug as a stale
- * skeleton — the on-demand file is what the agent executes at Phase 4.5.
- *
- * The regen renders into an isolated --out-dir and compares the rendered
- * bytes against the TRACKED files — the working tree is only ever read.
- */
-import { describe, test, expect } from 'bun:test';
-import * as fs from 'fs';
-import * as os from 'os';
-import * as path from 'path';
-import { spawnSync } from 'child_process';
-
-const ROOT = path.resolve(import.meta.dir, '..');
-
-const GENERATED_PATHS = [
-  path.join(ROOT, 'spec', 'SKILL.md'),
-  path.join(ROOT, 'spec', 'sections', 'gate-and-file.md'),
-];
-
-describe('/spec template/generated sync', () => {
-  test('regenerating spec/SKILL.md + sections produces byte-identical output', () => {
-    const outDir = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-spec-sync-'));
-
-    const res = spawnSync('bun', ['run', 'gen:skill-docs', '--out-dir', outDir], {
-      cwd: ROOT,
-      encoding: 'utf-8',
-      timeout: 120_000,
-      // Scrubbed env: bun test runs a shard's files serially in ONE process,
-      // so an earlier test's env mutations (GSTACK_*/GBRAIN_* detection vars)
-      // leak into inherited process.env and change generator output — this
-      // test failed in-suite while passing solo on an identical tree. The
-      // generator's output must be a function of the templates, not of
-      // whichever test ran before this one.
-      env: {
-        PATH: process.env.PATH ?? '',
-        HOME: process.env.HOME ?? '',
-        TMPDIR: process.env.TMPDIR ?? '',
-      },
-    });
-    try {
-      expect(res.status).toBe(0);
-
-      for (const trackedPath of GENERATED_PATHS) {
-        const rel = path.relative(ROOT, trackedPath);
-        const rendered = fs.readFileSync(path.join(outDir, rel), 'utf-8');
-        // --out-dir repoints the literal section-base paths
-        // (~/.claude/skills/gstack/<skill>/sections/ → <outDir>/<skill>/sections/)
-        // so section Reads resolve inside the render. Undo that single
-        // documented rewrite before comparing; every OTHER byte must match
-        // the tracked file exactly.
-        const normalized = rendered.replaceAll(`${outDir}/`, '~/.claude/skills/gstack/');
-        const tracked = fs.readFileSync(trackedPath, 'utf-8');
-        expect({ file: rel, identical: normalized === tracked })
-          .toEqual({ file: rel, identical: true });
-      }
-    } finally {
-      fs.rmSync(outDir, { recursive: true, force: true });
-    }
-  }, 130_000);
-
-  test('generated /spec docs carry the auto-generated header', () => {
-    for (const p of GENERATED_PATHS) {
-      const generated = fs.readFileSync(p, 'utf-8');
-      expect(generated).toMatch(/AUTO-GENERATED|do not edit directly/i);
-    }
-  });
-});