Resume sessions whose background subagents a restart killed

internal/agents/manager.go

@@ -35,6 +35,8 @@ const agentActor = "agent"
 
 const restartNotice = "byre restarted while you were mid-turn, so your last turn was cut off. Re-check the working tree (git status and the files you were editing) before continuing where you left off."
 
+const subagentsLostNotice = "Your agent process ended while background subagents you started were still running, so they were stopped and will never report back. Anything they found is lost; redo that work (run them again or do it yourself) and carry on where you left off."
+
 var progressSubtypes = map[string]bool{"status": true, "thinking_tokens": true}
 
 type Manager struct {
@@ -456,11 +458,15 @@ func (m *Manager) Recover(ctx context.Context) error {
 	if err != nil {
 		return err
 	}
+	orphaned := []string{}
 	for _, sess := range stale {
 		err = m.store.SetSubagents(ctx, sess.Id, 0, "byre")
 		if err != nil {
 			return err
 		}
+		if sess.State == api.AgentSessionStateIdle {
+			orphaned = append(orphaned, sess.Id)
+		}
 	}
 
 	sessions, err := m.store.SessionsInState(ctx, api.AgentSessionStateRunning)
@@ -488,6 +494,10 @@ func (m *Manager) Recover(ctx context.Context) error {
 		}
 	}
 
+	for _, id := range orphaned {
+		m.wakeOrphaned(ctx, id)
+	}
+
 	idle, err := m.store.SessionsInState(ctx, api.AgentSessionStateIdle)
 	if err != nil {
 		return err
@@ -508,6 +518,15 @@ func (m *Manager) Recover(ctx context.Context) error {
 	return nil
 }
 
+func (m *Manager) wakeOrphaned(ctx context.Context, sessionID string) {
+	_, _, err := m.Message(ctx, sessionID, "byre", Prompt{Text: subagentsLostNotice})
+	if err != nil {
+		slog.Error("wake session whose subagents were stopped", "session", sessionID, "err", err)
+		return
+	}
+	slog.Info("woke session whose subagents were stopped", "session", sessionID)
+}
+
 func (m *Manager) failResume(ctx context.Context, sess api.AgentSession, err error) error {
 	slog.Error("resume session", "session", sess.Id, "err", err)
 	if sess.Role == api.Reviewer {
@@ -982,7 +1001,8 @@ func (m *Manager) pump(l *live) {
 	quiet := closing || l.stopping
 	m.mu.Unlock()
 
-	if len(l.subagents) > 0 && !closing {
+	orphaned := len(l.subagents) > 0 && !closing
+	if orphaned {
 		err := m.store.SetSubagents(ctx, l.id, 0, "byre")
 		if err != nil {
 			slog.Error("clear exited session's subagents", "session", l.id, "err", err)
@@ -1000,6 +1020,10 @@ func (m *Manager) pump(l *live) {
 		return
 	}
 
+	if sess.State == api.AgentSessionStateIdle && orphaned {
+		m.wakeOrphaned(ctx, l.id)
+		return
+	}
 	if sess.State != api.AgentSessionStateRunning {
 		return
 	}