chore: bump version and changelog (v0.4.0)

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)