feat(ui): branch selectors in the GitLab merge request create form

packages/ui/src/components/views/GitLabMrView.tsx

@@ -12,11 +12,12 @@ import { useGitLabAuthStore } from '@/stores/useGitLabAuthStore';
 import { useUIStore } from '@/stores/useUIStore';
 import { openExternalUrl } from '@/lib/url';
 import { formatDateTimeForPreference } from '@/lib/timeFormat';
-import type { GitLabMergeRequestContextResult, GitLabMergeRequestSummary } from '@/lib/api/types';
+import type { GitLabMergeRequestContextResult, GitLabMergeRequestSummary, GitLabRepoRef } from '@/lib/api/types';
 import { useI18n } from '@/lib/i18n';
 import { toast } from '@/components/ui';
 import { Checkbox } from '@/components/ui/checkbox';
 import { Input } from '@/components/ui/input';
+import { Select, SelectContent, SelectItem, SelectTrigger, SelectValue } from '@/components/ui/select';
 import { Textarea } from '@/components/ui/textarea';
 
 const mrStateColor = (state: string): string => {
@@ -88,6 +89,7 @@ export const GitLabMrView: React.FC = () => {
   const [branchMrLoading, setBranchMrLoading] = React.useState(false);
   const [branchMrError, setBranchMrError] = React.useState<string | null>(null);
   const [retryToken, setRetryToken] = React.useState(0);
+  const [repoRef, setRepoRef] = React.useState<GitLabRepoRef | null>(null);
 
   const retry = React.useCallback(() => setRetryToken((value) => value + 1), []);
 
@@ -98,6 +100,11 @@ export const GitLabMrView: React.FC = () => {
     let cancelled = false;
     setBranchMrLoading(true);
     setBranchMrError(null);
+    // Re-resolving the repo context invalidates the previously fetched branch
+    // list so a stale repo's branches never leak into the create form.
+    setRepoRef(null);
+    setBranches([]);
+    setDefaultBranch(null);
     void gitlab
       .mrsList(currentDirectory, { sourceBranch: currentBranch })
       .then((result) => {
@@ -112,6 +119,7 @@ export const GitLabMrView: React.FC = () => {
           ?? candidates.find((mr) => mr.state === 'merged')
           ?? null;
         setBranchMr(matching);
+        setRepoRef(result.repo ?? null);
       })
       .catch((error) => {
         if (!cancelled) {
@@ -247,11 +255,26 @@ export const GitLabMrView: React.FC = () => {
 
   const [createTitle, setCreateTitle] = React.useState('');
   const [createDescription, setCreateDescription] = React.useState('');
+  const [createSourceBranch, setCreateSourceBranch] = React.useState(currentBranch ?? '');
   const [createTargetBranch, setCreateTargetBranch] = React.useState('main');
   const [createRemoveSourceBranch, setCreateRemoveSourceBranch] = React.useState(false);
   const [creating, setCreating] = React.useState(false);
   const createTargetTouchedRef = React.useRef(false);
 
+  // Repository branches for the source/target dropdowns, fetched lazily once
+  // the create form is visible.
+  const [branches, setBranches] = React.useState<string[]>([]);
+  const [defaultBranch, setDefaultBranch] = React.useState<string | null>(null);
+  const [branchesLoading, setBranchesLoading] = React.useState(false);
+
+  // The current branch is only known after git status resolves, so adopt it as
+  // the default source branch when it arrives without clobbering a pick.
+  React.useEffect(() => {
+    if (currentBranch) {
+      setCreateSourceBranch((previous) => previous || currentBranch);
+    }
+  }, [currentBranch]);
+
   // The default target branch is the target of the repository's previously
   // listed open MRs when available; otherwise fall back to main.
   const defaultTargetBranch = React.useMemo(
@@ -265,8 +288,62 @@ export const GitLabMrView: React.FC = () => {
     if (branchMrLoading || branchMr || createTargetTouchedRef.current) {
       return;
     }
-    setCreateTargetBranch(defaultTargetBranch);
-  }, [branchMr, branchMrLoading, defaultTargetBranch]);
+    setCreateTargetBranch(defaultBranch ?? defaultTargetBranch);
+  }, [branchMr, branchMrLoading, defaultBranch, defaultTargetBranch]);
+
+  // The source dropdown must always offer the picked/current branch, even
+  // before the branch list resolves.
+  const sourceBranchOptions = React.useMemo(() => {
+    if (!createSourceBranch) {
+      return branches;
+    }
+    return branches.includes(createSourceBranch) ? branches : [createSourceBranch, ...branches];
+  }, [branches, createSourceBranch]);
+
+  // A merge request cannot target its own source branch once there is more
+  // than one branch to choose from.
+  const targetBranchOptions = React.useMemo(
+    () => (branches.length >= 2 ? branches.filter((branch) => branch !== createSourceBranch) : branches),
+    [branches, createSourceBranch],
+  );
+
+  // Fetch the repository's branches lazily once the create form is visible so
+  // the source/target dropdowns can offer real values. Failure surfaces as a
+  // toast and leaves the dropdowns on the current-branch fallback.
+  React.useEffect(() => {
+    if (!repoRef || branchMr || !connected || !gitlab?.repoBranches) {
+      return;
+    }
+    let cancelled = false;
+    setBranchesLoading(true);
+    void gitlab
+      .repoBranches(repoRef.namespace, repoRef.project)
+      .then((result) => {
+        if (cancelled) {
+          return;
+        }
+        setBranches(result.branches ?? []);
+        setDefaultBranch(result.defaultBranch ?? null);
+      })
+      .catch((error) => {
+        if (cancelled) {
+          return;
+        }
+        setBranches([]);
+        setDefaultBranch(null);
+        toast.error(t('contextPanel.gitlabMr.error.loadFailed'), {
+          description: error instanceof Error ? error.message : String(error),
+        });
+      })
+      .finally(() => {
+        if (!cancelled) {
+          setBranchesLoading(false);
+        }
+      });
+    return () => {
+      cancelled = true;
+    };
+  }, [branchMr, connected, gitlab, repoRef, t]);
 
   const [updateOpen, setUpdateOpen] = React.useState(false);
   const [editTitle, setEditTitle] = React.useState('');
@@ -291,7 +368,7 @@ export const GitLabMrView: React.FC = () => {
       const created = await gitlab.mrCreate({
         directory: currentDirectory,
         title: createTitle.trim() || currentBranch,
-        sourceBranch: currentBranch,
+        sourceBranch: createSourceBranch,
         targetBranch,
         ...(createDescription.trim() ? { description: createDescription } : {}),
         ...(createRemoveSourceBranch ? { removeSourceBranch: true } : {}),
@@ -306,7 +383,7 @@ export const GitLabMrView: React.FC = () => {
       setCreateDescription('');
       setCreateRemoveSourceBranch(false);
       createTargetTouchedRef.current = false;
-      setCreateTargetBranch(defaultTargetBranch);
+      setCreateTargetBranch(defaultBranch ?? defaultTargetBranch);
     } catch (error) {
       toast.error(t('contextPanel.gitlabMr.createMr.toast.createFailed'), {
         description: error instanceof Error ? error.message : String(error),
@@ -314,7 +391,7 @@ export const GitLabMrView: React.FC = () => {
     } finally {
       setCreating(false);
     }
-  }, [createDescription, createRemoveSourceBranch, createTargetBranch, createTitle, currentBranch, currentDirectory, defaultTargetBranch, gitlab, t]);
+  }, [createDescription, createRemoveSourceBranch, createSourceBranch, createTargetBranch, createTitle, currentBranch, currentDirectory, defaultBranch, defaultTargetBranch, gitlab, t]);
 
   const toggleUpdate = React.useCallback(async () => {
     if (!branchMr) {
@@ -691,19 +768,36 @@ export const GitLabMrView: React.FC = () => {
 
               <label className="space-y-1">
                 <div className="typography-micro text-muted-foreground">{t('contextPanel.gitlabMr.createMr.sourceBranch')}</div>
-                <Input value={currentBranch} readOnly />
+                <Select value={createSourceBranch} onValueChange={(value) => setCreateSourceBranch(value)}>
+                  <SelectTrigger size="default" className="w-full">
+                    <SelectValue>{branchesLoading ? t('contextPanel.gitlabMr.createMr.branchesLoading') : createSourceBranch}</SelectValue>
+                  </SelectTrigger>
+                  <SelectContent>
+                    {sourceBranchOptions.map((branch) => (
+                      <SelectItem key={branch} value={branch}>{branch}</SelectItem>
+                    ))}
+                  </SelectContent>
+                </Select>
               </label>
 
               <label className="space-y-1">
                 <div className="typography-micro text-muted-foreground">{t('contextPanel.gitlabMr.createMr.targetBranch')}</div>
-                <Input
+                <Select
                   value={createTargetBranch}
-                  onChange={(event) => {
+                  onValueChange={(value) => {
                     createTargetTouchedRef.current = true;
-                    setCreateTargetBranch(event.target.value);
+                    setCreateTargetBranch(value);
                   }}
-                  placeholder="main"
-                />
+                >
+                  <SelectTrigger size="default" className="w-full">
+                    <SelectValue>{branchesLoading ? t('contextPanel.gitlabMr.createMr.branchesLoading') : createTargetBranch}</SelectValue>
+                  </SelectTrigger>
+                  <SelectContent>
+                    {targetBranchOptions.map((branch) => (
+                      <SelectItem key={branch} value={branch}>{branch}</SelectItem>
+                    ))}
+                  </SelectContent>
+                </Select>
               </label>
 
               <label className="space-y-1">

packages/ui/src/lib/api/types.ts

@@ -1145,7 +1145,7 @@ export type GitLabUserSummary = {
   email?: string;
 };
 
-type GitLabRepoRef = {
+export type GitLabRepoRef = {
   namespace: string;
   project: string;
   host: string;
@@ -1258,6 +1258,7 @@ export type GitLabMergeRequestContextResult = {
 
 export type GitLabBranchesResult = {
   branches: string[];
+  defaultBranch?: string | null;
 };
 
 export type GitLabMergeRequestCreateInput = {
@@ -1340,7 +1341,7 @@ export interface GitLabAPI {
   mrUpdate(input: GitLabMergeRequestUpdateInput): Promise<GitLabMergeRequest>;
   mrMerge(input: GitLabMergeRequestMergeInput): Promise<GitLabMergeRequestMergeResult>;
 
-  repoBranches(namespace: string, project: string): Promise<string[]>;
+  repoBranches(namespace: string, project: string): Promise<GitLabBranchesResult>;
 }
 
 export interface RemoteClientRecord {

packages/ui/src/lib/i18n/messages/de.ts

@@ -3011,6 +3011,7 @@ export const dict = {
   'contextPanel.gitlabMr.createMr.removeSourceBranch': 'Quellbranch nach dem Zusammenführen löschen',
   'contextPanel.gitlabMr.createMr.submit': 'Merge-Request erstellen',
   'contextPanel.gitlabMr.createMr.submitting': 'Wird erstellt...',
+  'contextPanel.gitlabMr.createMr.branchesLoading': 'Branches werden geladen...',
   'contextPanel.gitlabMr.createMr.toast.created': 'Merge-Request erstellt',
   'contextPanel.gitlabMr.createMr.toast.createFailed': 'Merge-Request konnte nicht erstellt werden',
   'contextPanel.gitlabMr.updateMr.toggle': 'Titel und Beschreibung bearbeiten',

packages/ui/src/lib/i18n/messages/en.ts

@@ -1148,6 +1148,7 @@ export const dict = {
   'contextPanel.gitlabMr.createMr.removeSourceBranch': 'Remove source branch on merge',
   'contextPanel.gitlabMr.createMr.submit': 'Create merge request',
   'contextPanel.gitlabMr.createMr.submitting': 'Creating...',
+  'contextPanel.gitlabMr.createMr.branchesLoading': 'Loading branches...',
   'contextPanel.gitlabMr.createMr.toast.created': 'Merge request created',
   'contextPanel.gitlabMr.createMr.toast.createFailed': 'Failed to create merge request',
   'contextPanel.gitlabMr.updateMr.toggle': 'Edit title & description',

packages/ui/src/lib/i18n/messages/es.ts

@@ -1149,6 +1149,7 @@ export const dict: Record<I18nKey, string> = {
   "contextPanel.gitlabMr.createMr.removeSourceBranch": "Eliminar la rama de origen al fusionar",
   "contextPanel.gitlabMr.createMr.submit": "Crear solicitud de fusión",
   "contextPanel.gitlabMr.createMr.submitting": "Creando...",
+  "contextPanel.gitlabMr.createMr.branchesLoading": "Cargando ramas...",
   "contextPanel.gitlabMr.createMr.toast.created": "Solicitud de fusión creada",
   "contextPanel.gitlabMr.createMr.toast.createFailed": "No se pudo crear la solicitud de fusión",
   "contextPanel.gitlabMr.updateMr.toggle": "Editar título y descripción",

packages/ui/src/lib/i18n/messages/fr.ts

@@ -968,6 +968,7 @@ export const dict = {
   'contextPanel.gitlabMr.createMr.removeSourceBranch': 'Supprimer la branche source lors de la fusion',
   'contextPanel.gitlabMr.createMr.submit': 'Créer une demande de fusion',
   'contextPanel.gitlabMr.createMr.submitting': 'Création...',
+  'contextPanel.gitlabMr.createMr.branchesLoading': 'Chargement des branches...',
   'contextPanel.gitlabMr.createMr.toast.created': 'Demande de fusion créée',
   'contextPanel.gitlabMr.createMr.toast.createFailed': 'Échec de la création de la demande de fusion',
   'contextPanel.gitlabMr.updateMr.toggle': 'Modifier le titre et la description',

packages/ui/src/lib/i18n/messages/ja.ts

@@ -1145,6 +1145,7 @@ export const dict: Record<I18nKey, string> = {
   'contextPanel.gitlabMr.createMr.removeSourceBranch': 'マージ時にソースブランチを削除する',
   'contextPanel.gitlabMr.createMr.submit': 'マージリクエストを作成',
   'contextPanel.gitlabMr.createMr.submitting': '作成中...',
+  'contextPanel.gitlabMr.createMr.branchesLoading': 'ブランチを読み込み中...',
   'contextPanel.gitlabMr.createMr.toast.created': 'マージリクエストを作成しました',
   'contextPanel.gitlabMr.createMr.toast.createFailed': 'マージリクエストの作成に失敗しました',
   'contextPanel.gitlabMr.updateMr.toggle': 'タイトルと説明を編集',

packages/ui/src/lib/i18n/messages/ko.ts

@@ -1149,6 +1149,7 @@ export const dict: Record<I18nKey, string> = {
   'contextPanel.gitlabMr.createMr.removeSourceBranch': '병합 시 소스 브랜치 삭제',
   'contextPanel.gitlabMr.createMr.submit': '병합 요청 만들기',
   'contextPanel.gitlabMr.createMr.submitting': '만드는 중...',
+  'contextPanel.gitlabMr.createMr.branchesLoading': '브랜치 불러오는 중...',
   'contextPanel.gitlabMr.createMr.toast.created': '병합 요청이 생성되었습니다',
   'contextPanel.gitlabMr.createMr.toast.createFailed': '병합 요청 생성에 실패했습니다',
   'contextPanel.gitlabMr.updateMr.toggle': '제목 및 설명 편집',

packages/ui/src/lib/i18n/messages/pl.ts

@@ -1486,6 +1486,7 @@ export const dict: Record<I18nKey, string> = {
   'contextPanel.gitlabMr.createMr.removeSourceBranch': 'Usuń gałąź źródłową po scaleniu',
   'contextPanel.gitlabMr.createMr.submit': 'Utwórz żądanie scalenia',
   'contextPanel.gitlabMr.createMr.submitting': 'Tworzenie...',
+  'contextPanel.gitlabMr.createMr.branchesLoading': 'Wczytywanie gałęzi...',
   'contextPanel.gitlabMr.createMr.toast.created': 'Utworzono żądanie scalenia',
   'contextPanel.gitlabMr.createMr.toast.createFailed': 'Nie udało się utworzyć żądania scalenia',
   'contextPanel.gitlabMr.updateMr.toggle': 'Edytuj tytuł i opis',

packages/ui/src/lib/i18n/messages/pt-BR.ts

@@ -1149,6 +1149,7 @@ export const dict: Record<I18nKey, string> = {
   "contextPanel.gitlabMr.createMr.removeSourceBranch": "Remover branch de origem ao mesclar",
   "contextPanel.gitlabMr.createMr.submit": "Criar solicitação de merge",
   "contextPanel.gitlabMr.createMr.submitting": "Criando...",
+  "contextPanel.gitlabMr.createMr.branchesLoading": "Carregando branches...",
   "contextPanel.gitlabMr.createMr.toast.created": "Solicitação de merge criada",
   "contextPanel.gitlabMr.createMr.toast.createFailed": "Falha ao criar solicitação de merge",
   "contextPanel.gitlabMr.updateMr.toggle": "Editar título e descrição",

packages/ui/src/lib/i18n/messages/uk.ts

@@ -1149,6 +1149,7 @@ export const dict: Record<I18nKey, string> = {
   "contextPanel.gitlabMr.createMr.removeSourceBranch": "Видалити вихідну гілку після злиття",
   "contextPanel.gitlabMr.createMr.submit": "Створити запит на злиття",
   "contextPanel.gitlabMr.createMr.submitting": "Створення...",
+  "contextPanel.gitlabMr.createMr.branchesLoading": "Завантаження гілок...",
   "contextPanel.gitlabMr.createMr.toast.created": "Запит на злиття створено",
   "contextPanel.gitlabMr.createMr.toast.createFailed": "Не вдалося створити запит на злиття",
   "contextPanel.gitlabMr.updateMr.toggle": "Редагувати назву та опис",

packages/ui/src/lib/i18n/messages/zh-CN.ts

@@ -1149,6 +1149,7 @@ export const dict: Record<I18nKey, string> = {
   'contextPanel.gitlabMr.createMr.removeSourceBranch': '合并后删除源分支',
   'contextPanel.gitlabMr.createMr.submit': '创建合并请求',
   'contextPanel.gitlabMr.createMr.submitting': '创建中...',
+  'contextPanel.gitlabMr.createMr.branchesLoading': '正在加载分支...',
   'contextPanel.gitlabMr.createMr.toast.created': '合并请求已创建',
   'contextPanel.gitlabMr.createMr.toast.createFailed': '创建合并请求失败',
   'contextPanel.gitlabMr.updateMr.toggle': '编辑标题和描述',

packages/ui/src/lib/i18n/messages/zh-TW.ts

@@ -1161,6 +1161,7 @@ export const dict: Record<I18nKey, string> = {
   'contextPanel.gitlabMr.createMr.removeSourceBranch': '合併後刪除來源分支',
   'contextPanel.gitlabMr.createMr.submit': '建立合併請求',
   'contextPanel.gitlabMr.createMr.submitting': '建立中...',
+  'contextPanel.gitlabMr.createMr.branchesLoading': '正在載入分支...',
   'contextPanel.gitlabMr.createMr.toast.created': '合併請求已建立',
   'contextPanel.gitlabMr.createMr.toast.createFailed': '建立合併請求失敗',
   'contextPanel.gitlabMr.updateMr.toggle': '編輯標題與描述',

packages/web/server/lib/gitlab/DOCUMENTATION.md

@@ -101,7 +101,7 @@ Nothing in the client or repo layers assumes the token came from a PAT.
 | POST | `/api/gitlab/mrs/create` | body `{ directory, title, sourceBranch, targetBranch, description?, removeSourceBranch? }` -> `{ connected, repo?, mr }`; `400` for missing fields, unresolvable repo, or a token without the `api` scope |
 | PUT | `/api/gitlab/mrs/update` | body `{ directory, number, title?, description? }` -> `{ connected, repo?, mr }`; `404` when the MR does not exist |
 | PUT | `/api/gitlab/mrs/merge` | body `{ directory, number, squash? }` -> `{ connected, merged: true }` on success; non-mergeable MRs -> the GitLab status (`405`/`406`/`409`/`422`) with `{ connected, merged: false, message }` |
-| GET | `/api/gitlab/repo/branches` | `?namespace&project` -> `{ branches[] }` |
+| GET | `/api/gitlab/repo/branches` | `?namespace&project` -> `{ branches[], defaultBranch? }` (`defaultBranch` is `null` when the repo has no marked default branch or GitLab is disconnected) |
 
 Conventions mirror `github/routes.js`:
 

packages/web/server/lib/gitlab/routes.js

@@ -876,10 +876,11 @@ export function registerGitLabRoutes(app, options = {}) {
 
       const client = await getClient();
       if (!client) {
-        return res.json({ branches: [] });
+        return res.json({ branches: [], defaultBranch: null });
       }
 
       const branches = [];
+      let defaultBranch = null;
       let page = 1;
       while (page <= 10) {
         const resp = await client.branches(`${namespace}/${project}`, { per_page: 100, page });
@@ -893,6 +894,9 @@ export function registerGitLabRoutes(app, options = {}) {
         for (const branch of chunk) {
           if (typeof branch?.name === 'string') {
             branches.push(branch.name);
+            if (defaultBranch === null && branch.default === true) {
+              defaultBranch = branch.name;
+            }
           }
         }
         if (chunk.length < 100 || !resp.page?.hasMore) {
@@ -901,7 +905,7 @@ export function registerGitLabRoutes(app, options = {}) {
         page += 1;
       }
 
-      return res.json({ branches });
+      return res.json({ branches, defaultBranch });
     } catch (error) {
       console.error('Failed to fetch GitLab repo branches:', error);
       return res.status(500).json({ error: error.message || 'Failed to fetch GitLab repo branches' });

packages/web/server/lib/gitlab/routes.test.js

@@ -490,7 +490,20 @@ describe('GitLab data routes', () => {
     expect(response.body.diff).toContain('line two');
   });
 
-  test('repo/branches returns branch names', async () => {
+  test('repo/branches returns branch names and the default branch', async () => {
+    scriptedFetch([
+      (url) => (matches(/\/repository\/branches\?/)(url)
+        ? jsonResponse([{ name: 'main', default: true }, { name: 'feat/api' }])
+        : null),
+    ]);
+
+    const app = createApp();
+    const response = await request(app).get('/api/gitlab/repo/branches?namespace=group&project=sub');
+    expect(response.status).toBe(200);
+    expect(response.body).toEqual({ branches: ['main', 'feat/api'], defaultBranch: 'main' });
+  });
+
+  test('repo/branches returns null defaultBranch when no branch is marked default', async () => {
     scriptedFetch([
       (url) => (matches(/\/repository\/branches\?/)(url)
         ? jsonResponse([{ name: 'main' }, { name: 'feat/api' }])
@@ -500,7 +513,15 @@ describe('GitLab data routes', () => {
     const app = createApp();
     const response = await request(app).get('/api/gitlab/repo/branches?namespace=group&project=sub');
     expect(response.status).toBe(200);
-    expect(response.body).toEqual({ branches: ['main', 'feat/api'] });
+    expect(response.body).toEqual({ branches: ['main', 'feat/api'], defaultBranch: null });
+  });
+
+  test('repo/branches returns empty branches and null defaultBranch when not connected', async () => {
+    clearGitLabAuth();
+    const app = createApp();
+    const response = await request(app).get('/api/gitlab/repo/branches?namespace=group&project=sub');
+    expect(response.status).toBe(200);
+    expect(response.body).toEqual({ branches: [], defaultBranch: null });
   });
 
   test('repo/branches requires namespace and project', async () => {

packages/web/src/api/gitlab.test.ts

@@ -263,6 +263,39 @@ describe('createWebGitLabAPI', () => {
     await expect(api.mrMerge({ directory: '/workspace', number: 12 })).rejects.toThrow('Bad Gateway');
   });
 
+  it('parses branches and the default branch from repoBranches', async () => {
+    runtimeFetchMock.mockResolvedValueOnce(Response.json({ branches: ['main', 'feat/api'], defaultBranch: 'main' }));
+
+    const api = await createAPI();
+    await expect(api.repoBranches('group', 'sub')).resolves.toEqual({ branches: ['main', 'feat/api'], defaultBranch: 'main' });
+
+    expect(runtimeFetchMock).toHaveBeenCalledWith('/api/gitlab/repo/branches?namespace=group&project=sub', {
+      method: 'GET',
+      headers: { Accept: 'application/json' },
+    });
+  });
+
+  it('defaults defaultBranch to null when repoBranches omits it', async () => {
+    runtimeFetchMock.mockResolvedValueOnce(Response.json({ branches: ['main'] }));
+
+    const api = await createAPI();
+    await expect(api.repoBranches('group', 'sub')).resolves.toEqual({ branches: ['main'], defaultBranch: null });
+  });
+
+  it('throws the server error message when repoBranches fails', async () => {
+    runtimeFetchMock.mockResolvedValueOnce(Response.json({ error: 'GitLab rate limited' }, { status: 503 }));
+
+    const api = await createAPI();
+    await expect(api.repoBranches('group', 'sub')).rejects.toThrow('GitLab rate limited');
+  });
+
+  it('throws the response status text when repoBranches has no parseable payload', async () => {
+    runtimeFetchMock.mockResolvedValueOnce(new Response('upstream gone', { status: 502, statusText: 'Bad Gateway' }));
+
+    const api = await createAPI();
+    await expect(api.repoBranches('group', 'sub')).rejects.toThrow('Bad Gateway');
+  });
+
   it('throws the server error message on {error} payloads', async () => {
     runtimeFetchMock.mockResolvedValueOnce(Response.json({ error: 'Not connected to GitLab' }, { status: 401 }));
 

packages/web/src/api/gitlab.ts

@@ -232,7 +232,7 @@ export const createWebGitLabAPI = ({ urls }: WebGitLabAPIOptions): GitLabAPI =>
     };
   },
 
-  async repoBranches(namespace: string, project: string): Promise<string[]> {
+  async repoBranches(namespace: string, project: string): Promise<GitLabBranchesResult> {
     const response = await runtimeFetch(
       `/api/gitlab/repo/branches?namespace=${encodeURIComponent(namespace)}&project=${encodeURIComponent(project)}`,
       { method: 'GET', headers: { Accept: 'application/json' } }
@@ -241,6 +241,9 @@ export const createWebGitLabAPI = ({ urls }: WebGitLabAPIOptions): GitLabAPI =>
     if (!response.ok || !body) {
       throw new Error(body?.error || response.statusText || 'Failed to fetch GitLab repo branches');
     }
-    return body.branches ?? [];
+    return {
+      branches: body.branches ?? [],
+      defaultBranch: body.defaultBranch ?? null,
+    };
   },
 });