Implement continuity handoffs and pickup validation

progress.md

@@ -36,12 +36,11 @@ This is the implementation-oriented breakdown of the specification. It is a proj
    - Done: native session usage readers and bounded current-turn occupancy calculation.
    - Done: anchor validation primitive for split-then-close rotation safety.
 
-6. **Continuity** — **not started**
-   - Handoff schema and validator
-   - CAS-backed handoffs/reports
-   - Immutable `TASK.md` handling
-   - Scratch-branch pickup contract
-   - Shared Markdown change notifications
+6. **Continuity** — **complete**
+   - Done: strict JSON handoff schema/validator, including framed knowledge fields and size-safe typed fields.
+   - Done: CAS-backed handoff save/load with content-address verification.
+   - Done: pickup validation against repository HEAD, dirty-file hashes, and immutable `TASK.md` hash.
+   - Done: scratch-branch WIP commit helper and Markdown change notices.
 
 7. **Authorization and surfaces** — **minimal groundwork only**
    - Done: a basic notify-only guard for Telegram/ntfy-style requests.
@@ -73,6 +72,7 @@ This is the implementation-oriented breakdown of the specification. It is a proj
 - Unit tests pass with `go test ./...`.
 - Implemented item 4 router assignment, lease-expiry polling, and retry policy.
 - Implemented item 5 herdr socket integration, harness adapters, native occupancy readers, bootstrap, and anchor validation.
+- Implemented item 6 continuity: validated CAS handoffs, pickup anchors/TASK.md, scratch-branch commits, and shared Markdown change notices.
 
 ## Current API additions