fix(herdr): close Phase 4 item 2 — actually ask the agent for a handoff

Release already validated and uploaded a §6.1 handoff, but nothing ever
told the agent the .orchestra-handoff.json convention existed, so the
file it waited on never got written. rotate() now prompts the agent
once via a new optional herdr.HandoffRequester capability
(CLIAdapter.RequestHandoff) when the file is missing, and defers
Release until it appears, mirroring the .orchestra-report.md/B3 ask
pattern rather than inventing a handoff.

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

progress.md

@@ -137,8 +137,22 @@ Fixed so far:
   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`).
+  **Was still open:** Phase 4 item 2 — nothing drove *any* harness to write
+  `.orchestra-handoff.json`, since Release only validated a file whose
+  existence was never solicited. **Closed 2026-07-27:** `rotate()` now checks
+  for the adapter's optional `herdr.HandoffRequester` capability; when
+  `HandoffFile` is missing at the worktree root, it prompts the agent once
+  (`CLIAdapter.RequestHandoff`, mirroring the `.orchestra-report.md`/B3
+  convention — the plane asks for a handoff, it never invents one) and skips
+  Release that tick, retrying every subsequent tick until the file appears.
+  `herdr.Session.HandoffRequested` avoids re-prompting every tick. Covered by
+  `TestRotationRequestsHandoffBeforeReleasing`
+  (`internal/orchestrator/rotation_test.go`), which asserts Release is never
+  called before the file exists and fires once it does. Codex/opencode still
+  share this same path (no harness-specific gap remains); the only leftover
+  question is whether each harness's own Stop-equivalent hook honors the
+  in-pane prompt to write the file before exiting, which is a live-deployment
+  fact, not something provable from source.
 
 Not yet started: B7 (quota projection has no producer),
 Codex/opencode completion producers, the turn-decision endpoint, S2–S4,