fix(continuity): wire scratch-commit-before-release and rewrite bootstrap prompt (Phase 4 items 3, 5, 6)

Release now re-verifies every handoff Anchor.Dirty file hash (previously
unchecked after the top-level anchor SHA compare), snapshots dirty state
onto a per-task scratch branch before uploading, and rewrites the anchor
to the new commit so successor pickup collapses to a single HEAD compare.
ScratchCommit made idempotent for repeated rotations of the same task.

Bootstrap's prompt now points the agent at the scratch-branch commit
history instead of vague "read the handoff" prose, and does not claim a
GET /v1/artifacts/<ref> endpoint that doesn't exist.

MarkdownChanges had zero callers and zero tests; deleted per AUDIT.md's
explicit deletion option rather than half-wiring an undesigned feature.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01W1rkJ2hBMybnJctPbcy4tT

progress.md

@@ -99,6 +99,47 @@ Fixed so far:
   named caveat: TASK.md hashing is best-effort and untested for the
   herdr-hosted (`WorktreeCreator`) worktree path.
 
+- **B5 (closed)** — `CLIAdapter.Release` previously just refused (no real
+  herdr method existed to call and there was nothing to validate against).
+  Now: reads the agent-authored `.orchestra-handoff.json` from the worktree
+  root, validates it with `continuity.Decode`, cross-checks its anchor SHA
+  against the worktree's real `HeadSHA` (never trusts the agent's self-report
+  outright), uploads it to CAS via `continuity.Save` to mint the
+  `handoff_ref`, and only then calls the real `pane.release_agent({pane_id,
+  source, agent})` to drop herdr's claim — sequenced last so a herdr-side
+  error can't strand an uploaded handoff. Any failure (missing file, invalid
+  schema, anchor mismatch, herdr error) is a refusal, which `rotate` already
+  treats as "retry next tick" rather than stranding the task. `herdr.Claude/
+  Codex/OpenCode` now take a `continuity.CAS` (main.go passes the existing
+  `*store.Store`). New tests in `internal/herdr/adapter_test.go` cover all
+  four paths against a real git worktree and a fake in-process herdr
+  listener. **Not done:** nothing yet makes the agent actually *write*
+  `.orchestra-handoff.json` (needs a stop-hook convention analogous to
+  `.orchestra-report.md`) — that and the rest of Phase 4 (ScratchCommit
+  before release, §6.2 bootstrap-prompt rewrite, `MarkdownChanges`) remain
+  open.
+
+- **Phase 4 items 3, 5, 6** — `CLIAdapter.Release` now re-verifies every
+  `Anchor.Dirty` file hash (previously only the top-level `Anchor.GitSHA`
+  was checked; a file edited after the handoff was written but before
+  release would have gone through unnoticed), then, if there were dirty
+  entries, snapshots them atomically onto a per-task scratch branch
+  (`continuity.ScratchCommit`, made idempotent so a task can rotate more
+  than once) and rewrites the handoff's anchor to that new commit with
+  `Dirty` cleared before uploading — so the successor's pickup check is a
+  single HEAD compare, not N file rehashes. `CLIAdapter.Bootstrap`'s prompt
+  was rewritten to point the agent at `git log`/the scratch branch instead
+  of a vague "read the handoff" instruction, and deliberately avoids
+  claiming a `GET /v1/artifacts/<ref>` endpoint, since no such route exists
+  (`/v1/artifacts` is POST-only). `continuity.MarkdownChanges` (§6.3
+  adjacent-task notice) had zero callers and zero tests despite being
+  listed as implemented in an earlier snapshot — deleted rather than
+  half-wired, per AUDIT.md's explicit "delete and record the deviation"
+  option. New tests: `TestReleaseScratchCommitsDirtyFilesBeforeUpload`,
+  `TestReleaseRefusesOnStaleDirtyFile` (internal/herdr/adapter_test.go).
+  **Not done:** Phase 4 item 2 (handoff production for Codex/opencode —
+  nothing yet drives those harnesses to write `.orchestra-handoff.json`).
+
 Not yet started: B7 (quota projection has no producer),
 Codex/opencode completion producers, the turn-decision endpoint, S2–S4,
 S7–S11. See `AUDIT.md` for the full plan.