feat(mastracode-web): single conversation per worktree in the sidebar

Multiple threads inside one worktree don't fit the workspace model — a
worktree is one unit of work. Nesting the multi-thread list (titles,
rename, clone, new-thread) under every workspace row added noise and
made it easy to scatter runs across stray threads.

The thread list now only nests under the main-branch workspace; feature
worktrees show no thread list, and the workspace row itself is the entry
point (selecting it resumes the worktree's latest thread or creates its
single one). Local projects keep the flat multi-thread list.

Co-Authored-By: Mastra Code (anthropic/claude-fable-5) <noreply@mastra.ai>

Author: abhiaiyer91

mastracode/web/src/web/ui/Sidebar.tsx

@@ -16,9 +16,10 @@ import { useOverlays } from './lib/overlays';
  * (`useActiveProjectContext`, focused chat hooks, `useOverlays`), so nothing is
  * wired through props here.
  *
- * Threads are scoped to the worktree they run in, so GitHub projects nest the
- * thread list under the active worktree inside the Workspaces section; local
- * projects (no worktrees) keep the flat list.
+ * Threads are scoped to the worktree they run in. GitHub projects nest the
+ * thread list under the main-branch workspace inside the Workspaces section —
+ * feature worktrees hold a single conversation, so they show no thread list;
+ * local projects (no worktrees) keep the flat list.
  */
 export function Sidebar() {
   const overlays = useOverlays();

mastracode/web/src/web/ui/domains/workspaces/components/WorkspacesSection.tsx

@@ -29,8 +29,11 @@ import type { Worktree } from '../services/projects';
  * Sidebar section listing a GitHub project's worktrees.
  *
  * Threads are scoped to the worktree they run in, so callers can pass the
- * thread list as `children`: it renders nested under the active worktree row
- * (or after the list when no worktree is selected yet).
+ * thread list as `children`. It only renders nested under the main-branch
+ * workspace (or after the list when no worktree is selected yet, which falls
+ * back to the main scope): feature worktrees hold a single conversation, so
+ * the workspace row itself is the entry point and no thread list (titles,
+ * rename, new-thread) is shown for them.
  */
 export function WorkspacesSection({ children }: { children?: ReactNode }) {
   const { baseUrl } = useApiConfig();
@@ -199,7 +202,10 @@ export function WorkspacesSection({ children }: { children?: ReactNode }) {
       <div className="flex flex-col gap-1">
         {worktrees.map(worktree => {
           const active = worktree.worktreePath === selectedPath;
-          const nested = active && Boolean(children);
+          // Feature worktrees hold a single conversation, so only the
+          // main-branch workspace nests the multi-thread list.
+          const isMainWorkspace = worktree.worktreePath === activeProject.sandboxWorkdir;
+          const nested = active && isMainWorkspace && Boolean(children);
           return (
             <div key={worktree.worktreePath} className="flex flex-col gap-1">
               <WorkspaceRow

mastracode/web/src/web/ui/domains/workspaces/components/__tests__/WorkspacesSection.msw.test.tsx

@@ -141,7 +141,7 @@ describe('WorkspacesSection', () => {
     expect(screen.getByRole('button', { name: 'feat-ui' })).not.toHaveAttribute('aria-current');
   });
 
-  it('nests children under the active worktree row', async () => {
+  it('nests children under the active main-branch workspace row', async () => {
     seedActiveProject(githubProject);
     useAgentControllerHandlers();
 
@@ -156,6 +156,17 @@ describe('WorkspacesSection', () => {
     expect(inactiveRow.parentElement?.parentElement).not.toContainElement(nested);
   });
 
+  it('given a feature worktree is active, then no thread list renders (worktrees hold a single conversation)', async () => {
+    seedActiveProject({ ...githubProject, selectedWorktreePath: '/sandbox/mastra-worktrees/feat-ui' });
+    useAgentControllerHandlers();
+
+    renderSection(<div data-testid="nested-threads">Threads</div>);
+
+    const activeRow = await screen.findByRole('button', { name: 'feat-ui' });
+    expect(activeRow).toHaveAttribute('aria-current', 'true');
+    expect(screen.queryByTestId('nested-threads')).not.toBeInTheDocument();
+  });
+
   it('does not render for local projects', async () => {
     seedActiveProject(localProject);
     useAgentControllerHandlers();