# overlay implementation plan
Status: implemented and verified.
Follow `AGENTS.md`; this file owns transient overlay tasks and proof.
## Work queue
- [x] `OVL-CONTRACT` - patch, operation, advisory, applied-provenance types.
- [x] `OVL-APPLY` - immutable application with edition, target, stale, and duplicate checks.
- [x] `OVL-BUILTIN` - evidence-backed IFC4 correction/advisory ledger.
- [x] `OVL-VERIFY` - official immutability and deliberate mutation tests.
## Completion log
Append concise task proof; no full logs.
- Overlay tests cover immutable snapshots, stale targets, duplicate IDs, provenance, advisories, and official-data preservation.