## Summary
- keeps lifecycle-census end-to-end fixtures valid after the conversion
backlog reaches zero
- treats zero backlog as a real protected end state instead of requiring
a remaining guard or claim target
- preserves nonzero rise/claim assertions when guards remain
## Test plan
- `corepack pnpm --filter @fusion/engine exec vitest run
src/__tests__/lifecycle-column-census.test.ts --silent=passed-only
--reporter=dot --project=engine-default`
- `corepack pnpm --filter @fusion/engine typecheck`
- verified the same suite at zero backlog on the aggregate runtime
(53/53)
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **Tests**
* Improved lifecycle validation to handle empty backlogs without errors.
* Added coverage for zero-item results and changing file sets.
* Enhanced baseline and trend checks to report completed backlogs
consistently.
* Improved resilience when expected result entries are unavailable,
ensuring validation completes cleanly with accurate zero counts.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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