Run the merge queue on a state-driven coordinator

internal/agents/mergemain.go

@@ -81,17 +81,14 @@ func (m *Manager) mergeToMain(ctx context.Context, l *live, raw json.RawMessage)
 		return "", err
 	}
 
-	pm := m.projectMerge(project.Id)
-	pm.mu.Lock()
-	holder := pm.holder
-	if holder == "" {
-		pm.holder = task.Id
+	holder, err := m.store.ClaimMainPush(ctx, task.Id)
+	if err != nil {
+		return "", err
 	}
-	pm.mu.Unlock()
 	if holder != "" {
 		return "", fmt.Errorf("%w: task %s is merging into %s; call again once it is done", ErrConflict, holder, project.DefaultBranch)
 	}
-	defer m.releaseMerge(project.Id, task.Id)
+	defer m.endMainPush(task.Id)
 
 	commit, err := m.pushToMain(ctx, l, task, project, user, title)
 	if err != nil {
@@ -170,6 +167,14 @@ func (m *Manager) pushToMain(ctx context.Context, l *live, task api.Task, projec
 	return commit, nil
 }
 
+func (m *Manager) endMainPush(taskID string) {
+	err := m.store.EndMainPush(context.Background(), taskID)
+	if err != nil {
+		slog.Error("end push to main", "task", taskID, "err", err)
+	}
+	m.poke()
+}
+
 func landPrompt(target, title string) string {
 	return fmt.Sprintf("The human asked to merge this task's work so far into %[1]s and keep the task open (Merge & continue); byre holds the task's other agents until this turn ends. "+
 		"First merge %[1]s in with `git merge --no-ff --no-commit %[1]s`, resolve any conflicts keeping both sides' intent, regenerate generated files instead of hand-merging them, and check that the build and tests pass. "+