fix(herdr): retry agent.start/agent.prompt through pane-boot readiness race (B12)

herdr hands a freshly created pane/agent back before it's actually ready,
and rejects the very next call with a range of different transient errors
("not an available shell", "not an active named agent", "target ... not
found") depending on timing. String-matching each wording as it turned up
live proved unwinnable across three live redeploy-and-test rounds, so
StartAgent and Prompt now retry any error for up to 15s (bounded by
wall-clock time, not attempt count) rather than pattern-matching herdr's
error text.

Confirmed live against workpc: a fresh lease (wD:p1) now reaches a real
attached claude session instead of failing before the agent starts.

Live testing also exposed a second, separate defect (B13, documented in
AUDIT.md, not fixed here): agent.start can return success while never
actually starting an agent when two leases land close together, with no
error for a retry to catch. Left three test panes on workpc untouched
(wD:p1, wE:p1, wF:p1) pending manual cleanup, per the standing rule against
destructive herdr calls without asking first.

Also folds in the already-flattened AUDIT.md/progress.md merge that was
staged ahead of this session's changes.

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

internal/herdr/herdr.go

@@ -165,12 +165,39 @@ type Session struct {
 	ConventionsHash string `json:"conventions_hash,omitempty"`
 }
 
+// bootDeadline bounds the retry loops below. Freshly created panes/agents
+// have been observed (live, 2026-07-28) to reject the very next call for a
+// range of different transient reasons as herdr finishes bringing them up —
+// "not an available shell", "not an active named agent", "target ... not
+// found" — a new wording each time a prior one got fixed. There is no other
+// legitimate reason a call against state orchestra itself just created would
+// fail immediately, so these loops retry any error rather than pattern-match
+// an open-ended and apparently still-growing set of herdr wordings, bounded
+// by wall-clock time rather than attempt count so a slow-booting pane still
+// gets the same real budget as a fast-failing one.
+const (
+	bootRetryWindow = 15 * time.Second
+	bootRetryDelay  = 500 * time.Millisecond
+)
+
 func (c *Client) Prompt(ctx context.Context, pane, text string, wait time.Duration) error {
 	p := map[string]any{"target": pane, "text": text}
 	if wait > 0 {
 		p["wait"] = map[string]any{"until": []string{"idle"}, "timeout_ms": wait.Milliseconds()}
 	}
-	return c.Call(ctx, "agent.prompt", p, nil)
+	deadline := time.Now().Add(bootRetryWindow)
+	var err error
+	for {
+		err = c.Call(ctx, "agent.prompt", p, nil)
+		if err == nil || time.Now().After(deadline) {
+			return err
+		}
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		case <-time.After(bootRetryDelay):
+		}
+	}
 }
 func (c *Client) Worktree(ctx context.Context, cwd, path, branch string) (string, error) {
 	var r worktreeResponse
@@ -204,15 +231,34 @@ func (c *Client) StartAgent(ctx context.Context, cwd, path, branch, harness, tas
 		return Session{}, fmt.Errorf("herdr: no pane recorded for worktree %s", path)
 	}
 	var s Session
-	if err := c.Call(ctx, "agent.start", map[string]any{
-		"pane_id": paneID,
-		"kind":    harness,
-		"name":    harness,
-		"args":    []string{},
-	}, &s); err != nil {
-		if !strings.Contains(strings.ToLower(err.Error()), "already") {
+	deadline := time.Now().Add(bootRetryWindow)
+	var err error
+	for {
+		s = Session{}
+		err = c.Call(ctx, "agent.start", map[string]any{
+			"pane_id": paneID,
+			"kind":    harness,
+			"name":    harness,
+			"args":    []string{},
+		}, &s)
+		if err == nil {
+			break
+		}
+		if strings.Contains(strings.ToLower(err.Error()), "already") {
+			err = nil
+			break
+		}
+		if time.Now().After(deadline) {
 			return Session{}, err
 		}
+		select {
+		case <-ctx.Done():
+			return Session{}, ctx.Err()
+		case <-time.After(bootRetryDelay):
+		}
+	}
+	if err != nil {
+		return Session{}, err
 	}
 	s.PaneID = paneID
 	s.Worktree = path