## What changed
- Preserve blocking merge-review reasons when `main` advances and the
clean-room squash must be rebuilt.
- Recover the latest unresolved blocking reason from task history when a
later merge retry starts.
- Require reviewers to validate prior blockers against the complete
resulting tree, not only a smaller residual diff.
- Add regression coverage for both concurrent-main rebuilds and durable
retry recovery.
## Why
A corrective clean-room squash can be approved and then discarded when
`main` advances before landing. The rebuild previously reset the
reviewer context, allowing a later, smaller squash to be approved and
the task to be finalized as Done without rechecking the original
correctness blocker.
## Impact
Tasks with unresolved blocking review findings can no longer become Done
merely because a concurrent rebuild or later retry loses that review
context.
## Validation
- `pnpm --filter @fusion/engine exec vitest run
src/__tests__/merger-ai.test.ts` — 45 passed
- `pnpm --filter @fusion/engine typecheck`
- ESLint on the changed merger source files
- Changeset format check
<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit
* **Bug Fixes**
* Merge and review blockers now remain active across rebuilds and retry
attempts.
* Previous blocking reasons are preserved alongside newly identified
issues.
* Empty corrective rebuilds are reviewed before being accepted as
complete.
* Tasks can no longer be finalized solely because a rebuilt diff is
smaller when unresolved blockers remain.
* **Documentation**
* Updated release notes to describe the improved blocker behavior.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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Co-authored-by: v <v@v.speedport.ip>
8f7f52784d