Hold a task's merge while another task in the project is merging

internal/agents/manager.go

@@ -66,6 +66,9 @@ type Manager struct {
 	setups        map[string]bool
 	setupFailures map[string]string
 
+	mergeMu      sync.Mutex
+	mergeHolders map[string]string
+
 	bad       *badLines
 	watchStop chan struct{}
 }
@@ -111,6 +114,7 @@ func New(st *store.Store, limits Limits, worktreeRoot, leadRoot string) *Manager
 		snaps:         map[string]*snapState{},
 		setups:        map[string]bool{},
 		setupFailures: map[string]string{},
+		mergeHolders:  map[string]string{},
 		bad:           newBadLines(),
 		watchStop:     make(chan struct{}),
 	}
@@ -270,6 +274,11 @@ func (m *Manager) retire(ctx context.Context, sess api.AgentSession, actor strin
 }
 
 func (m *Manager) Recover(ctx context.Context) error {
+	err := m.recoverMerges(ctx)
+	if err != nil {
+		return err
+	}
+
 	sessions, err := m.store.SessionsInState(ctx, api.AgentSessionStateRunning)
 	if err != nil {
 		return err
@@ -290,7 +299,7 @@ func (m *Manager) Recover(ctx context.Context) error {
 				return err
 			}
 			if sess.Owner == "" {
-				m.takeMerge(task.Id)
+				m.abandonMerge(task.Id, task.ProjectId)
 			}
 			continue
 		}
@@ -312,6 +321,7 @@ func (m *Manager) Recover(ctx context.Context) error {
 	}
 
 	go m.deliverAllLeads()
+	go m.startHeldMerges(context.Background())
 	return m.drain(ctx)
 }
 
@@ -764,7 +774,7 @@ func (m *Manager) pump(l *live) {
 		slog.Error("record session exit", "session", l.id, "err", err)
 	}
 	if l.owner == "" {
-		m.takeMerge(l.taskID)
+		m.abandonMerge(l.taskID, l.projectID)
 		m.fileError(l, "The agent process exited mid-turn. Send a message to resume it.")
 	}
 
@@ -925,10 +935,15 @@ func (m *Manager) handle(ctx context.Context, l *live, ev claude.Event) error {
 			return nil
 		}
 		mergeBy := m.takeMerge(l.taskID)
-		if mergeBy != "" && finished {
+		switch {
+		case mergeBy != "" && finished:
 			m.logUndelivered(ctx, l.id, "turn ended in merge")
 			go m.finishMerge(l, mergeBy)
 			return nil
+		case mergeBy != "":
+			go m.releaseMerge(l.projectID, l.taskID)
+		default:
+			go m.nextMerge(l.projectID)
 		}
 		err = m.Deliver(ctx, l.id)
 		if err != nil {