fix(projects): drop parent folders; attribute sessions to the deepest project

The projects panel listed bare parent folders (~, ~/Documents) as projects and
a single session lit up every ancestor project's 'Active now'. dropParentFolders
filters non-git entries that merely contain other listed projects; assignSessions
attributes each live session to the DEEPEST containing project (detail page keeps
prefix matching). +3 tests; projects 29/29, tsc clean. Frontend unchanged.

test/projects.test.ts

@@ -212,6 +212,28 @@ describe('buildProjects — session merge', () => {
     expect(repoA.sessions.find((s) => s.id === 's-under')!.title).toBe('http')
   })
 
+  it('attributes a session only to the DEEPEST project containing its cwd', async () => {
+    // repoA is discovered by the scan; the nested repoA/sub repo enters via
+    // history (scan does not descend into repos). A session inside sub must
+    // NOT also light up the ancestor repoA.
+    const repoPath = path.join(tmp, 'repoA')
+    const subPath = path.join(repoPath, 'sub')
+    await makeRepo(repoPath, 'main')
+    await makeRepo(subPath, 'dev')
+    mockListSessions.mockResolvedValue([
+      { id: 'h1', cwd: subPath, project: 'sub', mtimeMs: 1000, preview: '' },
+    ])
+    const cfg = makeCfg({ projectRoots: [tmp], projectScanDepth: 2, projectDirtyCheck: false })
+
+    const live = [makeLive({ id: 's-deep', cwd: path.join(subPath, 'src') })]
+    const out = await buildProjects(cfg, live)
+
+    const repoA = out.find((p) => p.path === repoPath)!
+    const sub = out.find((p) => p.path === subPath)!
+    expect(sub.sessions.map((s) => s.id)).toEqual(['s-deep'])
+    expect(repoA.sessions).toEqual([])
+  })
+
   it('re-merges live sessions FRESH on every call (discovery is cached)', async () => {
     await makeRepo(path.join(tmp, 'repoA'), 'main')
     const repoPath = path.join(tmp, 'repoA')
@@ -266,6 +288,36 @@ describe('buildProjects — history merge & sorting', () => {
     }
   })
 
+  it('drops non-git parent folders that merely contain other projects', async () => {
+    // Running a session in ~/Documents once puts it in history; it must not be
+    // listed as a project when it only contains real repos (parent folder).
+    const repoPath = path.join(tmp, 'repoA')
+    await makeRepo(repoPath, 'main')
+    mockListSessions.mockResolvedValue([
+      { id: 'h1', cwd: tmp, project: path.basename(tmp), mtimeMs: 2000, preview: '' },
+      { id: 'h2', cwd: repoPath, project: 'repoA', mtimeMs: 1000, preview: '' },
+    ])
+    const cfg = makeCfg({ projectRoots: [tmp], projectScanDepth: 2, projectDirtyCheck: false })
+
+    const out = await buildProjects(cfg, [])
+
+    expect(out.some((p) => p.path === tmp)).toBe(false) // parent folder dropped
+    expect(out.some((p) => p.path === repoPath)).toBe(true)
+  })
+
+  it('keeps a non-git history project that contains no other project', async () => {
+    const standalone = path.join(tmp, 'notes')
+    await fs.mkdir(standalone, { recursive: true })
+    mockListSessions.mockResolvedValue([
+      { id: 'h1', cwd: standalone, project: 'notes', mtimeMs: 2000, preview: '' },
+    ])
+    const cfg = makeCfg({ projectRoots: [tmp], projectScanDepth: 2, projectDirtyCheck: false })
+
+    const out = await buildProjects(cfg, [])
+
+    expect(out.some((p) => p.path === standalone)).toBe(true)
+  })
+
   it('sorts by lastActiveMs desc, undefined last, name asc tiebreak', async () => {
     await makeRepo(path.join(tmp, 'zzz'), 'main') // no history -> undefined
     await makeRepo(path.join(tmp, 'aaa'), 'main') // no history -> undefined