chore(#3053): clock-seam ADR-456 amendment + backfill — H2 (#3332)

* test(#3314): backfill deterministic clock-seam coverage (failing-first)

Replaces loose regex/range assertions with exact-value and boundary
tests for the CLI-subprocess and in-process clock-touching call sites
identified by H2's audit (epic #3053): cmdCurrentTimestamp,
_wsParseRetryAfter (commands.cts), cmdInitManager's is_active gate and
cmdInitQuick's quick_id generation (init.cts), and reapStaleTempFiles
(io.cts). The CLI-subprocess-pinned tests are expected RED until a
follow-up commit routes those call sites through realClock so
GSD_TEST_MODE+GSD_NOW_MS can reach them.

* refactor(#3314): route CLI-subprocess clock reads through realClock

cmdCurrentTimestamp, cmdInitManager's is_active gate, and cmdInitQuick's
quick_id generation read Date directly, which the GSD_TEST_MODE+GSD_NOW_MS
subprocess pin cannot reach (it only fires inside realClock.now()).
Behavior-preserving: realClock.now() falls through to Date.now() whenever
GSD_TEST_MODE is unset, which is every real invocation.

* docs(#3314): amend ADR-456 with reachability-based clock-control rule

ADR-456 §(a) documented one mechanism (injected {clock=Date} +
t.mock.timers). Adds the two this repo already relies on: t.mock.timers
for in-process direct-Date reads, and the GSD_TEST_MODE+GSD_NOW_MS
subprocess pin (routed through realClock) for CLI-spawned code. Updates
TESTING-STANDARDS.md's matching passages, which already referenced this
issue by number as the no-elapsed-assertion promotion precondition.

* fix(#3314): address orthogonal review findings

Spec-axis findings: file and link the no-elapsed-assertion promotion
follow-up (#3331) instead of leaving TESTING-STANDARDS.md pointing at
a dead #1885, and ship the module-by-module audit table in the ADR
itself rather than only in a gitignored phase artifact.

Standards-axis finding: pin the "hour-old file = not active" test via
GSD_TEST_MODE+GSD_NOW_MS for consistency with the reachability rule
this PR's own ADR amendment now documents.

---------

Co-authored-by: sim <sim@local>

tests/io.test.cjs

@@ -311,6 +311,45 @@ describe('reapStaleTempFiles (via io)', () => {
       io.reapStaleTempFiles('gsd-io-nonexistent-prefix-xyz-', { maxAgeMs: 0 });
     });
   });
+
+  // #3314 — ADR-456 in-process reachability: t.mock.timers patches the
+  // process-global Date, so it controls `now` inside reapStaleTempFiles with
+  // no production code change needed. Both sides of the comparison (mocked
+  // "now" and the fs.utimesSync mtime) use second-aligned epoch values to
+  // avoid filesystem mtime sub-second-precision truncation on filesystems
+  // that round mtime to the nearest second.
+  describe('boundary: age exactly at maxAgeMs (condition is strictly-greater)', () => {
+    const MTIME_MS = 1_700_000_000_000; // second-aligned
+    const MAX_AGE_MS = 5000;
+
+    function plantFileAtAge(t, ageMs) {
+      fs.mkdirSync(io.GSD_TEMP_DIR, { recursive: true });
+      const p = path.join(io.GSD_TEMP_DIR, TEST_PREFIX + `boundary-${ageMs}.json`);
+      fs.writeFileSync(p, '{}');
+      fs.utimesSync(p, new Date(MTIME_MS), new Date(MTIME_MS));
+      t.mock.timers.enable(['Date']);
+      t.mock.timers.setTime(MTIME_MS + ageMs);
+      return p;
+    }
+
+    test('boundary: age exactly maxAgeMs-1 is kept', (t) => {
+      const p = plantFileAtAge(t, MAX_AGE_MS - 1);
+      io.reapStaleTempFiles(TEST_PREFIX, { maxAgeMs: MAX_AGE_MS });
+      assert.ok(fs.existsSync(p), 'file at maxAgeMs-1 must be kept');
+    });
+
+    test('boundary: age exactly maxAgeMs is kept (condition is strictly-greater)', (t) => {
+      const p = plantFileAtAge(t, MAX_AGE_MS);
+      io.reapStaleTempFiles(TEST_PREFIX, { maxAgeMs: MAX_AGE_MS });
+      assert.ok(fs.existsSync(p), 'file at exactly maxAgeMs must be kept — condition is strictly-greater, not >=');
+    });
+
+    test('boundary: age exactly maxAgeMs+1 is removed', (t) => {
+      const p = plantFileAtAge(t, MAX_AGE_MS + 1);
+      io.reapStaleTempFiles(TEST_PREFIX, { maxAgeMs: MAX_AGE_MS });
+      assert.ok(!fs.existsSync(p), 'file at maxAgeMs+1 must be removed');
+    });
+  });
 });