decompose reconciler roadmap into 20 implementation tasks across 5 phases

Tasks follow the architecture spec phases:
- Phase 0: key field on UElement (2 tasks + review)
- Phase 1: reactive-host bridge / fiber tree (4 tasks + review)
- Phase 2: key-based children reconciliation (3 tasks + review)
- Phase 3: unmount & dispose support (4 tasks)
- Phase 4: TypeBox value optimizations (4 tasks)

Validated with taskgraph CLI: no cycles, 15 parallel generations,
3 high-risk tasks identified (signal-driven-updates, commit-mutations,
fiber-disposal).

tasks/value-equal-bailout.md

@@ -0,0 +1,48 @@
+---
+id: value-equal-bailout
+name: Value.Equal bail-out for unchanged subtrees
+status: pending
+depends_on: [review-reconciler]
+created: 2026-05-18T16:22:57.339429429Z
+modified: 2026-05-18T16:22:57.339429873Z
+scope: narrow
+risk: low
+impact: component
+level: implementation
+---
+
+# Description
+
+Add `Value.Equal` as the first TypeBox optimization layer. When reconciling, if a fiber's cached node is deep-equal to the next node, skip the entire subtree — no `prepareUpdate`, no `commitUpdate`, no children reconciliation.
+
+This is the highest-impact optimization according to the architecture doc because it skips entire subtrees. It's also the simplest to implement and has no constraints (unlike `Value.Hash` which has the global accumulator issue).
+
+The optimization is applied during `reconcileProps`:
+```
+if Value.Equal(fiber.cachedNode, nextNode):
+  return  // skip this fiber and all children
+```
+
+## Acceptance Criteria
+
+- [ ] `Value.Equal` check added before property reconciliation
+- [ ] If fiber's cached node equals next node, skip `prepareUpdate` and children reconciliation
+- [ ] Cached node stored on fiber (new `cachedNode` field or reuse `props` snapshot)
+- [ ] Correctness: behavior is identical with and without the optimization
+- [ ] Existing tests pass
+- [ ] New test: unchanged subtree skips `prepareUpdate`/`commitUpdate`
+- [ ] New test: changed prop still triggers `prepareUpdate`
+- [ ] New test: deeply nested unchanged subtree is fully skipped
+
+## References
+
+- docs/architecture/reconciler.md — TypeBox Optimization Layer, Value.Equal row
+- docs/architecture/reconciler.md — Optimization Strategy (step 1)
+
+## Notes
+
+> To be filled by implementation agent
+
+## Summary
+
+> To be filled on completion