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

internal/orchestrator/orchestrator.go

@@ -499,6 +499,20 @@ func (c *Coordinator) rotate(ctx context.Context, hard float64) {
 		} else {
 			c.recordTurnBoundaryDegraded()
 		}
+		if requester, ok := a.(herdr.HandoffRequester); ok {
+			if _, statErr := os.Stat(filepath.Join(session.Worktree, herdr.HandoffFile)); statErr != nil {
+				if !session.HandoffRequested {
+					if reqErr := requester.RequestHandoff(ctx, session); reqErr == nil {
+						session.HandoffRequested = true
+						c.mu.Lock()
+						c.sessions[taskID] = session
+						_ = c.saveSessionsLocked()
+						c.mu.Unlock()
+					}
+				}
+				continue
+			}
+		}
 		ref, err := a.Release(ctx, session)
 		if err != nil {
 			continue