---
id: review-reconciler
name: Review key-based reconciliation
status: pending
depends_on: [commit-mutations]
created: 2026-05-18T16:22:57.261831485Z
modified: 2026-05-18T16:22:57.261831927Z
scope: narrow
risk: low
impact: phase
level: review
---

# Description

Review the full key-based reconciliation implementation before proceeding to unmount/dispose. This checkpoint verifies that the reconciler correctly handles add, remove, reorder, and update operations for both keyed and unkeyed children.

This is important because Phase 3 (dispose) will add teardown logic that depends on the reconciliation algorithm correctly identifying removed fibers. If reconciliation misclassifies a child as "removed" when it should be "moved," disposal will destroy an instance that still exists.

## Acceptance Criteria

- [ ] Keyed children: add/remove/reorder all produce correct host calls
- [ ] Unkeyed children: positional matching works for prop updates
- [ ] Mixed keyed + unkeyed: key-based for keyed, positional for unkeyed
- [ ] Duplicate keys: last-wins, no crash, warn logged
- [ ] Commit order: removes → inserts/moves → updates
- [ ] `insertBefore` used for moves and inserts with a target sibling
- [ ] Fiber tree structure matches the new UNode tree after reconciliation
- [ ] No orphaned fibers (removed fibers are pruned from parent's children)
- [ ] No leaked host instances (every `removeChild` called for removed fibers)
- [ ] Signal-driven prop updates still work alongside structural reconciliation
- [ ] All tests pass including host integration tests

## References

- docs/architecture/reconciler.md — Full reconciliation algorithm
- docs/architecture/lifecycle.md — Disposal depends on correct remove classification

## Notes

> To be filled on completion of review

## Summary

> To be filled on completion