fix: keep launch context rail on one line

Long branch names should be clipped inside the branch selector instead of forcing the repository context rail onto a second row. The rail now stays nowrap, the branch selector owns truncation, and the worktree mode selector keeps its readable fixed footprint.

Constraint: Preserve the existing composer and repository context layout shape.
Rejected: Let the rail wrap on long branch names | it creates the broken two-line state shown in the desktop composer.
Confidence: high
Scope-risk: narrow
Directive: Long repository or branch labels must truncate inside their own controls rather than changing the rail height.
Tested: cd desktop && bun run test -- --run src/pages/EmptySession.test.tsx src/components/chat/ChatInput.test.tsx src/components/shared/DirectoryPicker.test.tsx
Tested: bun run check:desktop
Tested: agent-browser selected a long branch on http://localhost:4790 and verified rail height 53px, branch width 260px, no horizontal overflow; screenshot /tmp/cc-haha-launch-rail-long-branch-nowrap.png
Not-tested: Native Tauri packaged window visual check

desktop/src/components/shared/RepositoryLaunchControls.tsx

@@ -298,11 +298,11 @@ export function RepositoryLaunchControls({
   }, [isLaunchReady, onLaunchReadyChange])
 
   const worktreeLabel = useWorktree ? t('repoLaunch.worktreeIsolated') : t('repoLaunch.worktreeCurrent')
-  const workbarButtonClassName = 'group inline-flex h-9 max-w-full min-w-0 items-center gap-1.5 rounded-[7px] border border-transparent px-2.5 text-[13px] font-medium leading-none text-[var(--color-text-secondary)] transition-colors hover:bg-[var(--color-surface-container-lowest)] focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-[var(--color-brand)]/35 disabled:cursor-not-allowed disabled:opacity-50'
+  const workbarButtonClassName = 'group inline-flex h-9 min-w-0 items-center gap-1.5 rounded-[7px] border border-transparent px-2.5 text-[13px] font-medium leading-none text-[var(--color-text-secondary)] transition-colors hover:bg-[var(--color-surface-container-lowest)] focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-[var(--color-brand)]/35 disabled:cursor-not-allowed disabled:opacity-50'
 
   return (
     <div ref={rootRef} className="flex min-w-0 flex-col gap-2">
-      <div className="flex min-h-[48px] min-w-0 flex-wrap items-center justify-start gap-x-1.5 gap-y-1 rounded-b-xl border-t border-[var(--color-border-separator)] bg-[var(--color-surface-container-low)] px-4 py-2 shadow-[inset_0_1px_0_rgba(255,255,255,0.45)]">
+      <div className="flex min-h-[48px] min-w-0 flex-nowrap items-center justify-start gap-x-1.5 gap-y-1 overflow-hidden rounded-b-xl border-t border-[var(--color-border-separator)] bg-[var(--color-surface-container-low)] px-4 py-2 shadow-[inset_0_1px_0_rgba(255,255,255,0.45)]">
         <DirectoryPicker value={workDir} onChange={onWorkDirChange} variant="workbar" isGitProject={isGitReady} />
 
         {loading && workDir && (
@@ -328,7 +328,7 @@ export function RepositoryLaunchControls({
                 setWorktreeMenuOpen(false)
                 setBranchFilter('')
               }}
-              className={`${workbarButtonClassName} max-w-[260px]`}
+              className={`${workbarButtonClassName} max-w-[260px] shrink`}
             >
               <GitBranch size={17} className="shrink-0 text-[var(--color-text-tertiary)] group-hover:text-[var(--color-text-secondary)]" />
               <span className="min-w-0 flex-1 truncate text-[var(--color-text-primary)]">
@@ -350,7 +350,7 @@ export function RepositoryLaunchControls({
                 setWorktreeMenuOpen((prev) => !prev)
                 setBranchMenuOpen(false)
               }}
-              className={`${workbarButtonClassName} ${
+              className={`${workbarButtonClassName} shrink-0 ${
                 useWorktree
                   ? 'bg-[var(--color-surface-container-lowest)] text-[var(--color-text-primary)]'
                   : ''

desktop/src/pages/EmptySession.test.tsx

@@ -304,6 +304,42 @@ describe('EmptySession', () => {
     })
   })
 
+  it('keeps the repository launch context on one row and truncates long branch names', async () => {
+    const longBranch = 'feature/super-long-branch-name-for-repository-launch-controls-e2e'
+    mocks.getRepositoryContext.mockResolvedValueOnce(okRepositoryContext({
+      currentBranch: longBranch,
+      defaultBranch: 'main',
+      branches: [{
+        name: longBranch,
+        current: true,
+        local: true,
+        remote: false,
+        checkedOut: true,
+        worktreePath: '/workspace/project',
+      }],
+      worktrees: [{
+        path: '/workspace/project',
+        branch: longBranch,
+        current: true,
+      }],
+    }))
+
+    render(<EmptySession />)
+
+    fireEvent.change(screen.getByRole('textbox'), {
+      target: { value: 'draft question', selectionStart: 14 },
+    })
+    fireEvent.click(screen.getByRole('button', { name: 'Pick project' }))
+
+    const branchButton = await screen.findByRole('button', { name: new RegExp(`Select branch: ${longBranch}`) })
+    const branchClasses = branchButton.className.split(/\s+/)
+    expect(branchButton.parentElement?.className).toContain('flex-nowrap')
+    expect(branchButton.parentElement?.className).not.toContain('flex-wrap')
+    expect(branchClasses).toContain('max-w-[260px]')
+    expect(branchClasses).not.toContain('max-w-full')
+    expect(branchButton.querySelector('span')?.className).toContain('truncate')
+  })
+
   it('defaults to isolated worktree when the fallback branch is checked out elsewhere', async () => {
     mocks.getRepositoryContext.mockResolvedValueOnce(okRepositoryContext({
       currentBranch: null,