fix(desktop): restore folder-pick affordance and filter sidebar to session-bearing projects

PR #49037 (projects paradigm) broke the folder->session->sidebar flow (#53004):

- The right sidebar's Files pane gated the tree on $currentCwd, which is ''
  for global/detached sessions, so those sessions hit a dead-end 'No project
  open' pane with no way back into a folder. Restore an affordance in the
  empty state: 'Open folder' runs the existing open-folder-as-project flow
  (upsert + enter project + fresh session anchored at the picked folder),
  decoupled from $currentCwd.
- The sidebar overview listed every auto-promoted repo on disk, session or
  not. Auto projects with zero sessions now stay out of the sidebar until
  they own a session (they reappear the moment work lands there); explicit
  projects and the Home bucket always render.

UI-affecting: coordinator should hold auto-merge for visual review.

Fixes #53004

apps/desktop/src/app/chat/sidebar/index.tsx

@@ -157,7 +157,7 @@ import { orderByIds, reconcileOrderIds, resolveManualSessionOrderIds, sameIds }
 import { filterSessionsByProfileScope } from './profile-scope'
 import { ProfileRail } from './profile-switcher'
 import { ProjectDialog } from './project-dialog'
-import { resolveLiveProjectFilter } from './project-filter'
+import { filterToSessionBearingProjects, resolveLiveProjectFilter } from './project-filter'
 import {
   excludeProjectSessions,
   orderProjectsByIds,
@@ -1013,7 +1013,7 @@ export function ChatSidebar({
   // overview sort. Membership is the backend tree's — never re-derived here.
   const projectModel = useMemo<SidebarProjectTree[]>(() => {
     const sorted = sortProjectsForOverview(
-      filterVisibleProjects(projectTree, dismissedAutoProjects)
+      filterToSessionBearingProjects(filterVisibleProjects(projectTree, dismissedAutoProjects))
         // A filtered-out project drops its whole lane, header included — hiding
         // only its rows would leave a row of empty folders behind.
         .filter(project => !projectFilter.length || projectFilter.includes(project.id))

apps/desktop/src/app/chat/sidebar/project-filter.test.ts

@@ -1,6 +1,6 @@
 import { describe, expect, it } from 'vitest'
 
-import { resolveLiveProjectFilter } from './project-filter'
+import { filterToSessionBearingProjects, resolveLiveProjectFilter } from './project-filter'
 
 describe('resolveLiveProjectFilter', () => {
   const treeA = [{ id: 'p_aaa' }, { id: '/Users/me/repos/alpha' }] as const
@@ -34,3 +34,28 @@ describe('resolveLiveProjectFilter', () => {
     expect(resolveLiveProjectFilter(['p_aaa'], undefined)).toEqual([])
   })
 })
+
+describe('filterToSessionBearingProjects (#53004)', () => {
+  const base = { label: 'repo', path: '/tmp/repo', repos: [] } as const
+
+  const tree = [
+    { ...base, id: 'auto_empty', isAuto: true, sessionCount: 0 },
+    { ...base, id: 'auto_active', isAuto: true, sessionCount: 2 },
+    { ...base, id: 'explicit_empty', sessionCount: 0 },
+    { ...base, id: 'home', isNoProject: true, sessionCount: 0 }
+  ]
+
+  it('drops auto projects with no sessions but keeps active autos', () => {
+    const ids = filterToSessionBearingProjects(tree).map(project => project.id)
+
+    expect(ids).not.toContain('auto_empty')
+    expect(ids).toContain('auto_active')
+  })
+
+  it('never drops explicit projects or the Home bucket', () => {
+    const ids = filterToSessionBearingProjects(tree).map(project => project.id)
+
+    expect(ids).toContain('explicit_empty')
+    expect(ids).toContain('home')
+  })
+})

apps/desktop/src/app/chat/sidebar/project-filter.ts

@@ -20,3 +20,19 @@ export function resolveLiveProjectFilter(
 
   return projectFilter.filter(id => liveIds.has(id))
 }
+
+/**
+ * The sidebar overview is a session history, not a disk browser (#53004): an
+ * auto-promoted repo with no sessions yet stays out of the sidebar until work
+ * lands there (it reappears the moment it owns a session). Explicit projects
+ * and the Home bucket always render — the user created or kept those. Session
+ * counts come from the backend `projects.tree`, so this stays live without
+ * client-side re-derivation.
+ */
+export function filterToSessionBearingProjects<
+  T extends { isAuto?: boolean; isNoProject?: boolean; sessionCount?: number }
+>(projects: readonly T[]): T[] {
+  return projects.filter(
+    project => !project.isAuto || project.isNoProject || (project.sessionCount ?? 0) > 0
+  )
+}

apps/desktop/src/app/right-sidebar/index.tsx

@@ -13,6 +13,7 @@ import { cn } from '@/lib/utils'
 import { $panesFlipped } from '@/store/layout'
 import { notifyError } from '@/store/notifications'
 import { openPreview } from '@/store/preview'
+import { openFolderAsProject } from '@/store/projects'
 import { $currentCwd, $selectedStoredSessionId, $workspaceCwdOwner } from '@/store/session'
 
 import { SidebarPanelLabel } from '../shell/sidebar-label'
@@ -149,10 +150,22 @@ function FilesystemTab({
   const { t } = useI18n()
   const r = t.rightSidebar
 
-  // No working directory (a bare/detached chat) → no tree, just a terse hint.
-  // Switching workspace is a project/worktree action, never a raw folder picker.
+  // No working directory (a bare/detached chat) → no tree, but keep a way back
+  // into a folder (#53004): the projects paradigm removed the old folder picker,
+  // which stranded global sessions on a dead-end "No project open" pane. The
+  // affordance is the project-shaped one — ⌘O's open-folder-as-project flow,
+  // which upserts/enters the project and anchors a fresh session at the picked
+  // folder — entirely decoupled from $currentCwd.
   if (!hasWorkspace) {
-    return <PaneEmptyState label={r.noProjectOpen} />
+    return (
+      <div className="flex min-h-0 flex-1 flex-col items-center justify-center gap-2 px-4 text-center">
+        <SidebarPanelLabel className="pl-0 text-(--ui-text-quaternary)">{r.noProjectOpen}</SidebarPanelLabel>
+        <Button className="h-7 gap-1.5 text-xs" onClick={() => void openFolderAsProject()} size="sm" variant="outline">
+          <Codicon name="folder-opened" size="0.8125rem" />
+          {r.openFolder}
+        </Button>
+      </div>
+    )
   }
 
   return (