fix(box): structured agents resume and switch on linux, and say what they do in order

internal/box/acpdriver.go

@@ -214,7 +214,9 @@ func (c *acpConv) follow() {
 		c.mu.Lock()
 		from, done := c.lastSeq, c.exited
 		c.mu.Unlock()
-		if done {
+		if done && !hostAlive(c.sock) {
+			// Its last word was its end, and no host has started since. (A
+			// host started again listens a moment before it says so.)
 			return
 		}
 		err := agenthost.Attach(context.Background(), c.sock, from, func(e agenthost.Entry) error {
@@ -341,7 +343,9 @@ func (c *acpConv) apply(e agenthost.Entry, live bool) {
 		case m.Method != "" && len(m.ID) > 0:
 			c.sent[string(m.ID)] = m.Method
 		case m.Method == "" && len(m.ID) > 0:
-			c.drop(string(m.ID))
+			if c.drop(string(m.ID)) && live {
+				say = append(say, func() { c.event(adapters.Started, map[string]any{"signal": "tool"}, nil) })
+			}
 		}
 		return
 	case "out":
@@ -519,13 +523,14 @@ func (c *acpConv) readSession(raw json.RawMessage) {
 	}
 }
 
-func (c *acpConv) drop(id string) {
+func (c *acpConv) drop(id string) bool {
 	for i, r := range c.pending {
 		if string(r.ID) == id {
 			c.pending = append(c.pending[:i], c.pending[i+1:]...)
-			return
+			return true
 		}
 	}
+	return false
 }
 
 // ask is what a permission asks, as a hook's ask is.
@@ -736,11 +741,9 @@ func (c *acpConv) choose(r acpRequest, optionID string) error {
 	if optionID == "" {
 		result = map[string]any{"outcome": map[string]any{"outcome": "cancelled"}}
 	}
-	err := c.write(context.Background(), map[string]any{"jsonrpc": "2.0", "id": r.ID, "result": result})
-	if err == nil {
-		c.event(adapters.Started, map[string]any{"signal": "tool"}, nil)
-	}
-	return err
+	// Working again is said when the answer is read back from the log
+	// (apply), before anything the agent says after it.
+	return c.write(context.Background(), map[string]any{"jsonrpc": "2.0", "id": r.ID, "result": result})
 }
 
 // allow says yes to a permission, for this time or always.

internal/box/claudedriver.go

@@ -310,7 +310,9 @@ func (c *claudeConv) follow() {
 		c.mu.Lock()
 		from, done := c.lastSeq, c.exited
 		c.mu.Unlock()
-		if done {
+		if done && !hostAlive(c.sock) {
+			// Its last word was its end, and no host has started since. (A
+			// host started again listens a moment before it says so.)
 			return
 		}
 		err := agenthost.Attach(context.Background(), c.sock, from, func(e agenthost.Entry) error {
@@ -414,7 +416,10 @@ func (c *claudeConv) apply(e agenthost.Entry, live bool) {
 	case "in":
 		var l streamLine
 		if json.Unmarshal(e.Data, &l) == nil && l.Type == "control_response" && l.Response != nil {
-			c.drop(l.Response.RequestID)
+			if c.drop(l.Response.RequestID) && live {
+				// Answered: the tool runs, or the agent goes on without it.
+				say = append(say, func() { c.event(adapters.Started, map[string]any{"signal": "tool"}, nil) })
+			}
 		}
 		return
 	case "out":
@@ -527,15 +532,16 @@ func (c *claudeConv) apply(e agenthost.Entry, live bool) {
 	}
 }
 
-// drop forgets a permission that was answered or withdrawn. Called with
-// c.mu held.
-func (c *claudeConv) drop(id string) {
+// drop forgets a permission that was answered or withdrawn, and says
+// whether it was waiting. Called with c.mu held.
+func (c *claudeConv) drop(id string) bool {
 	for i, r := range c.pending {
 		if r.ID == id {
 			c.pending = append(c.pending[:i], c.pending[i+1:]...)
-			return
+			return true
 		}
 	}
+	return false
 }
 
 // reconcile tells the ledger what the log says now, after a restart read
@@ -738,10 +744,8 @@ func (c *claudeConv) respond(r claudeRequest, resp map[string]any) error {
 	err := c.write(context.Background(), map[string]any{"type": "control_response", "response": map[string]any{
 		"subtype": "success", "request_id": r.ID, "response": resp,
 	}})
-	if err == nil {
-		// The tool runs, or the agent goes on without it: working again.
-		c.event(adapters.Started, map[string]any{"signal": "tool"}, nil)
-	}
+	// Working again is said when the answer is read back from the log
+	// (apply), before anything the agent says after it.
 	return err
 }
 
@@ -1057,6 +1061,18 @@ func (b *Box) forgetConversation(name string) {
 	b.acp().forget(name)
 }
 
+// hostAlive says whether a host answers on sock.
+func hostAlive(sock string) bool {
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+	defer cancel()
+	c, err := agenthost.Dial(ctx, sock)
+	if err != nil {
+		return false
+	}
+	c.Close()
+	return true
+}
+
 // awaitHost waits up to d for a session's host to listen.
 func awaitHost(sock string, d time.Duration) bool {
 	deadline := time.Now().Add(d)

internal/box/codexdriver.go

@@ -214,7 +214,9 @@ func (c *codexConv) follow() {
 		c.mu.Lock()
 		from, done := c.lastSeq, c.exited
 		c.mu.Unlock()
-		if done {
+		if done && !hostAlive(c.sock) {
+			// Its last word was its end, and no host has started since. (A
+			// host started again listens a moment before it says so.)
 			return
 		}
 		err := agenthost.Attach(context.Background(), c.sock, from, func(e agenthost.Entry) error {

internal/box/switch.go

@@ -35,8 +35,9 @@ import (
 // back (Session.Switch "chat").
 
 // labelHandoff is where Claude Code's transcript stood when the session
-// went to its terminal: the file, then its size. What it says past that
-// was said in the terminal.
+// went to its terminal: its size, a space, then the file. What it says past
+// that was said in the terminal. (Printable only: tmux on Linux shows a
+// control character in an option escaped.)
 const labelHandoff = "@berth_handoff"
 
 // SwitchRequest moves a session to its terminal or back to its chat.
@@ -126,7 +127,7 @@ func (b *Box) toTerminal(r *http.Request, sess Session) error {
 	handoff := ""
 	if _, path, _ := b.transcriptFile(ctx, sess, nil); path != "" {
 		if st, err := os.Stat(path); err == nil {
-			handoff = path + "\x1f" + strconv.FormatInt(st.Size(), 10)
+			handoff = strconv.FormatInt(st.Size(), 10) + " " + path
 		}
 	}
 	stopCtx, cancel := context.WithTimeout(ctx, 30*time.Second)
@@ -198,7 +199,7 @@ func (b *Box) importTerminalTurns(ctx context.Context, sess Session) error {
 	if err != nil {
 		return nil
 	}
-	path, off, ok := strings.Cut(strings.TrimSpace(string(v)), "\x1f")
+	off, path, ok := strings.Cut(strings.TrimSpace(string(v)), " ")
 	from, perr := strconv.ParseInt(off, 10, 64)
 	if !ok || perr != nil || path == "" {
 		return nil
@@ -245,19 +246,21 @@ func lastSessionID(path string) string {
 
 // respawnAgent runs command in the session's pane in place of what ran
 // there, with env added to the session's own and labels set, as create
-// starts one (sessions.go).
+// starts one (sessions.go): with its agent's CLI on PATH, which a login
+// shell may otherwise lose (Debian's resets it).
 func (b *Box) respawnAgent(ctx context.Context, sess Session, command string, env []string, labels map[string]string) error {
+	agent := firstNonEmpty(agentFor(sess), "claude")
 	s := b.Sessions
 	extra, wrap := b.sessionEnv(ctx, sess.Dir)
 	file, err := s.writeCommand(sess.Name, command)
 	if err != nil {
 		return err
 	}
 	shell := sessionShell()
-	argv := []string{shell, "-lc", withPATH(shell, launchPATH(command, "claude"), sourceCommand(shell, file))}
+	argv := []string{shell, "-lc", withPATH(shell, launchPATH(command, agent), sourceCommand(shell, file))}
 	target := "=" + sess.Name + ":"
 	args := []string{"respawn-pane", "-k", "-t", target, "-c", sess.Dir}
-	for _, kv := range append(append(withAgentBrowserIdle(extra), "BERTH_SESSION="+sess.Name, "BERTH_AGENT=claude"), env...) {
+	for _, kv := range append(append(withAgentBrowserIdle(extra), "BERTH_SESSION="+sess.Name, "BERTH_AGENT="+agent), env...) {
 		args = append(args, "-e", kv)
 	}
 	args = append(append(args, "--"), groups.Wrap(append(append([]string(nil), wrap...), argv...))...)