# S04 Post-Slice Assessment

**Verdict:** Roadmap unchanged. No slice reordering, merging, splitting, or description changes needed.

## Risk Retirement

S04 retired its medium risk on schedule. Checkpoint→modify→restore cycle, undo round-trip, error paths, and process liveness after errors all proven by integration tests. The RefCell interior mutability pattern (D029) is consistent with existing D014 pattern — no fragility introduced.

## Success Criteria Coverage

All 7 success criteria have at least one remaining owning slice (S05, S06, S07) or are already proven (S01, S03, S04). No gaps.

## Boundary Map Accuracy

S04 → S05 boundary holds. S05 consumes:
- `BackupStore.snapshot()` via `ctx.backup().borrow_mut()` — exactly as built
- `CheckpointStore` for checkpoint-aware batch rollback — available through AppContext
- Parser/symbols from S02 — accessed via `ctx.provider()`

One addition not in the original boundary map: AppContext (D025) is now the dispatch mechanism. S05 handlers will follow the `(&RawRequest, &AppContext) -> Response` signature (D026). This is already documented in decisions and S04 summary.

## Requirement Coverage

- R007 (per-file auto-backup): advanced by S04, full validation blocked on S05 wiring auto-snapshot into edit commands. Coverage remains sound.
- R008 (workspace checkpoints): functionally complete in S04. End-to-end proof with mutation commands deferred to S05 integration tests.
- No requirements invalidated, re-scoped, or newly surfaced.
- Remaining active requirements (R004–R006, R009–R012) still map to S05/S06/S07 as planned.

## Next Slice

S05 (Three-Layer Editing Engine) is unblocked — both dependencies (S02, S04) are complete.
