feat: QA restructure, browser ref staleness, eval efficiency metrics (v0.4.0) (#83)

* feat: browser ref staleness detection via async count() validation

resolveRef() now checks element count to detect stale refs after page
mutations (e.g. SPA navigation). RefEntry stores role+name metadata
for better diagnostics. 3 new snapshot tests for staleness detection.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: qa-only skill, qa fix loop, plan-to-QA artifact flow

Add /qa-only (report-only, Edit tool blocked), restructure /qa with
find-fix-verify cycle, add {{QA_METHODOLOGY}} DRY placeholder for
shared methodology. /plan-eng-review now writes test-plan artifacts
to ~/.gstack/projects/<slug>/ for QA consumption.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: eval efficiency metrics — turns, duration, commentary across all surfaces

Add generateCommentary() for natural-language delta interpretation,
per-test turns/duration in comparison and summary output, judgePassed
unit tests, 3 new E2E tests (qa-only, qa fix loop, plan artifact).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* chore: bump version and changelog (v0.4.0)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* docs: update ARCHITECTURE, BROWSER, CONTRIBUTING, README for v0.4.0

- ARCHITECTURE: add ref staleness detection section, update RefEntry type
- BROWSER: add ref staleness paragraph to snapshot system docs
- CONTRIBUTING: update eval tool descriptions with commentary feature
- README: fix missing qa-only in project-local uninstall command

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* docs: add user-facing benefit descriptions to v0.4.0 changelog

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

TODOS.md

@@ -350,6 +350,30 @@
 **Priority:** P3
 **Depends on:** Eval persistence (shipped in v0.3.6)
 
+### CI/CD QA quality gate
+
+**What:** Run `/qa` as a GitHub Action step, fail PR if health score drops below threshold.
+
+**Why:** Automated quality gate catches regressions before merge. Currently QA is manual — CI integration makes it part of the standard workflow.
+
+**Context:** Requires headless browse binary available in CI. The `/qa` skill already produces `baseline.json` with health scores — CI step would compare against the main branch baseline and fail if score drops. Would need `ANTHROPIC_API_KEY` in CI secrets since `/qa` uses Claude.
+
+**Effort:** M
+**Priority:** P2
+**Depends on:** None
+
+### CDP-based DOM mutation detection for ref staleness
+
+**What:** Use Chrome DevTools Protocol `DOM.documentUpdated` / MutationObserver events to proactively invalidate stale refs when the DOM changes, without requiring an explicit `snapshot` call.
+
+**Why:** Current ref staleness detection (async count() check) only catches stale refs at action time. CDP mutation detection would proactively warn when refs become stale, preventing the 5-second timeout entirely for SPA re-renders.
+
+**Context:** Parts 1+2 of ref staleness fix (RefEntry metadata + eager validation via count()) are shipped. This is Part 3 — the most ambitious piece. Requires CDP session alongside Playwright, MutationObserver bridge, and careful performance tuning to avoid overhead on every DOM change.
+
+**Effort:** L
+**Priority:** P3
+**Depends on:** Ref staleness Parts 1+2 (shipped)
+
 ## Completed
 
 ### Phase 1: Foundations (v0.2.0)