refactor(#1191): inject clock/reset testability seams + handle valid-null settings (#1233)

* refactor(#1191): inject clock/reset testability seams + handle valid-null settings

- worktree-safety reapOrphanWorktrees: injectable deps.nowMs clock for deterministic stale-lock boundary tests (mirrors snapshotWorktreeInventory's options.nowMs).

- active-workstream-store: _resetControllingTtyCacheForTests() seam clears the memoized controlling-TTY probe cache; test replaces require.cache busting.

- gen-capability-registry: export stripGeneratedComment (additive); test imports the real helper + equivalence assertion, keeping the deliberate drift oracle.

- install.js readSettings: a successfully-parsed JSON null is treated as empty settings ({}) instead of being mis-reported as malformed; genuine parse failures still warn. readSettings/stripJsonComments exported (GSD_TEST_MODE-guarded require) for real behavioral tests.

Closes #1191

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* chore(#1191): add changeset for valid-null settings fix (#1233)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* fix(#1191): replace Stryker-incompatible structural reset test with behavioral isTTY-spy

The seam-2 reset test read the BUILT active-workstream-store.cjs and grepped for 'didProbeControllingTtyToken = false' — Stryker instruments that file so the literal is absent, failing the mutation DRY RUN. Replaced with a behavioral test that spies on process.stdin.isTTY access count to prove a post-reset probe re-runs (kills the didProbe-reset mutant) without reading source text. Local stryker: dry run passes, score 85.21% >= 80.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

src/active-workstream-store.cts

@@ -49,6 +49,12 @@ function sanitizeWorkstreamSessionToken(value: unknown): string | null {
   return token ? token.slice(0, 160) : null;
 }
 
+/** Test-only seam: clear the memoized controlling-TTY probe cache (#1191). */
+function _resetControllingTtyCacheForTests(): void {
+  cachedControllingTtyToken = null;
+  didProbeControllingTtyToken = false;
+}
+
 function probeControllingTtyToken(): string | null {
   if (didProbeControllingTtyToken) return cachedControllingTtyToken;
   didProbeControllingTtyToken = true;
@@ -347,4 +353,5 @@ export = {
   parseCliWorkstream,
   resolveActiveWorkstream,
   applyResolvedWorkstreamEnv,
+  _resetControllingTtyCacheForTests,
 };

src/worktree-safety.cts

@@ -100,6 +100,8 @@ interface WorktreeDeps {
   readFileSafe?: (file: string) => string | null;
   mtimeSafe?: (file: string) => Date | null;
   reapMtimeGuardMs?: number;
+  /** Injected current time in ms since epoch for deterministic tests (#1191). */
+  nowMs?: number;
   parseWorktreePorcelain?: (porcelain: string) => WorktreeBranchEntry[];
 }
 
@@ -878,6 +880,7 @@ function reapOrphanWorktrees(repoRoot: string, deps: WorktreeDeps = {}): ReapRes
   const readFileSafe = deps.readFileSafe || defaultReadFileSafe;
   const mtimeSafe = deps.mtimeSafe || defaultMtimeSafe;
   const reapMtimeGuardMs = deps.reapMtimeGuardMs !== undefined ? deps.reapMtimeGuardMs : REAP_MTIME_GUARD_MS;
+  const nowMs = deps.nowMs ?? Date.now();
 
   const results: ReapResult[] = [];
 
@@ -982,7 +985,7 @@ function reapOrphanWorktrees(repoRoot: string, deps: WorktreeDeps = {}): ReapRes
 
     // 4a. Stale-lock guard: skip if lock is too fresh (PID recycling / race).
     const lockMtime = mtimeSafe(lockedFile);
-    if (!lockMtime || Date.now() - lockMtime.getTime() < reapMtimeGuardMs) {
+    if (!lockMtime || nowMs - lockMtime.getTime() < reapMtimeGuardMs) {
       results.push({ path: worktreePath, status: 'skipped', reason: 'lock_too_fresh' });
       continue;
     }