Edit the drafted merge message before confirming

internal/agents/leadtools.go

@@ -270,7 +270,7 @@ func (m *Manager) leadTools(l *live) []mcp.Tool {
 				if err != nil {
 					return "", err
 				}
-				task, err = m.Merge(ctx, task, project, user)
+				task, err = m.Merge(ctx, task, project, user, task.MergeTitle)
 				if err != nil {
 					return "", err
 				}

internal/agents/mergein.go

@@ -18,20 +18,23 @@ import (
 
 const maxMergeTitle = 72
 
-func mergeInPrompt(target, mergeTitle string) string {
+func mergeInPrompt(target string) string {
 	return fmt.Sprintf("Merge %[1]s into this branch: run `git merge --no-ff --no-commit %[1]s`. "+
 		"Resolve any conflicts keeping both sides' intent; regenerate generated files instead of hand-merging them. "+
-		"Check that the build and tests pass. Leave the merge uncommitted: byre concludes it when the turn ends. "+
-		"Finally, if the merge commit title (currently \"%[2]s\") no longer describes all the work on this branch, set a better one with set_merge_title.", target, mergeTitle)
+		"Check that the build and tests pass. Leave the merge uncommitted: byre concludes it when the turn ends.", target)
 }
 
 func (m *Manager) MergeIn(ctx context.Context, task api.Task, user api.User, target string) (api.AgentSession, error) {
+	prompt := mergeInPrompt(target) + fmt.Sprintf(" Finally, if the merge commit title (currently \"%s\") no longer describes all the work on this branch, set a better one with set_merge_title.", task.MergeTitle)
+	return m.sendMergeIn(ctx, task, user, prompt)
+}
+
+func (m *Manager) sendMergeIn(ctx context.Context, task api.Task, user api.User, prompt string) (api.AgentSession, error) {
 	sessions, err := m.store.ListSessions(ctx, task.Id)
 	if err != nil {
 		return api.AgentSession{}, err
 	}
 
-	prompt := mergeInPrompt(target, task.MergeTitle)
 	for _, sess := range sessions {
 		if sess.State != api.AgentSessionStateCompleted {
 			return m.Send(ctx, sess.Id, "byre", prompt, "")
@@ -41,20 +44,33 @@ func (m *Manager) MergeIn(ctx context.Context, task api.Task, user api.User, tar
 	return m.create(ctx, task, user, prompt, "", "byre", nil)
 }
 
-func (m *Manager) Merge(ctx context.Context, task api.Task, project api.Project, user api.User) (api.Task, error) {
+func (m *Manager) Merge(ctx context.Context, task api.Task, project api.Project, user api.User, title string) (api.Task, error) {
 	if user.GitName == "" || user.GitEmail == "" {
 		return api.Task{}, ErrNoGitIdentity
 	}
 	if task.MergeQueuedAt != nil {
 		return api.Task{}, fmt.Errorf("%w: task %s is already waiting to merge", ErrConflict, task.Id)
 	}
+	title, err := cleanMergeTitle(title)
+	if err != nil {
+		return api.Task{}, err
+	}
 
 	m.mergeMu.Lock()
 	defer m.mergeMu.Unlock()
 
-	switch m.mergeHolders[project.Id] {
-	case task.Id:
+	if m.mergeHolders[project.Id] == task.Id {
 		return api.Task{}, fmt.Errorf("%w: task %s is already merging", ErrConflict, task.Id)
+	}
+	if title != task.MergeTitle {
+		err = m.storeMergeTitle(ctx, task.Id, title, user.Login)
+		if err != nil {
+			return api.Task{}, err
+		}
+		task.MergeTitle = title
+	}
+
+	switch m.mergeHolders[project.Id] {
 	case "":
 		err := m.startMerge(ctx, task, project, user)
 		if err != nil {
@@ -84,7 +100,7 @@ func (m *Manager) startMerge(ctx context.Context, task api.Task, project api.Pro
 	}
 	m.mergeHolders[project.Id] = task.Id
 
-	_, err = m.MergeIn(ctx, task, user, project.DefaultBranch)
+	_, err = m.sendMergeIn(ctx, task, user, mergeInPrompt(project.DefaultBranch))
 	if err != nil {
 		m.takeMerge(task.Id)
 		delete(m.mergeHolders, project.Id)
@@ -367,20 +383,33 @@ func (m *Manager) setMergeTitle(ctx context.Context, l *live, raw json.RawMessag
 		return "", fmt.Errorf("malformed set_merge_title call: %w", err)
 	}
 
-	title := strings.TrimSpace(args.Title)
-	if title == "" || strings.ContainsAny(title, "\r\n") {
-		return "", errors.New("title must be one non-empty line")
-	}
-	if utf8.RuneCountInString(title) > maxMergeTitle {
-		return "", fmt.Errorf("title is %d characters; keep it to %d", utf8.RuneCountInString(title), maxMergeTitle)
+	title, err := cleanMergeTitle(args.Title)
+	if err != nil {
+		return "", err
 	}
 
-	err = m.store.SetMergeTitle(ctx, l.taskID, title, agentActor)
-	if errors.Is(err, store.ErrNotFound) {
-		return "", errors.New("this task is no longer active")
-	}
+	err = m.storeMergeTitle(ctx, l.taskID, title, agentActor)
 	if err != nil {
 		return "", err
 	}
 	return fmt.Sprintf("Merge commit title set to %q.", title), nil
 }
+
+func cleanMergeTitle(raw string) (string, error) {
+	title := strings.TrimSpace(raw)
+	if title == "" || strings.ContainsAny(title, "\r\n") {
+		return "", fmt.Errorf("%w: title must be one non-empty line", ErrInvalid)
+	}
+	if utf8.RuneCountInString(title) > maxMergeTitle {
+		return "", fmt.Errorf("%w: title is %d characters; keep it to %d", ErrInvalid, utf8.RuneCountInString(title), maxMergeTitle)
+	}
+	return title, nil
+}
+
+func (m *Manager) storeMergeTitle(ctx context.Context, taskID, title, actor string) error {
+	err := m.store.SetMergeTitle(ctx, taskID, title, actor)
+	if errors.Is(err, store.ErrNotFound) {
+		return fmt.Errorf("%w: this task is closed, or its merge was already confirmed with its title", ErrConflict)
+	}
+	return err
+}