feat(ui-workspace): archive session from the row menu

The visual-only Delete session placeholder becomes a wired Archive
session action: no confirmation dialog (non-destructive), failures stay
console diagnostics. tree.ts hides archived sessions in every
derivation (workspace groups, Ungrouped, search, flat list) through the
sessionVisible predicate. The workspace-management e2e pins the archive
round trip across reload.

packages/client/ui-workspace/tests/workspace-browser.spec.tsx

@@ -35,8 +35,8 @@ const workspace = (id: string, sessionIds: string[], title = id): WorkspaceView
   workspaceId: wid(id), path: `/projects/${id}`, title,
   sessionIds: sessionIds.map(sid), createdAt: '2026-01-01T00:00:00.000Z', updatedAt: '2026-01-01T00:00:00.000Z',
 })
-const workspaceState = (items: readonly WorkspaceView[]): WorkspaceListState => ({
-  items, state: 'idle', phase: 'ready', error: null, baselinesReady: true,
+const workspaceState = (items: readonly WorkspaceView[], archivedSessionIds: ReadonlySet<SessionId> = new Set()): WorkspaceListState => ({
+  items, archivedSessionIds, state: 'idle', phase: 'ready', error: null, baselinesReady: true,
   recentWorkspaceId: items[0]?.workspaceId,
 })
 function hook<T>(snapshot: T) {
@@ -68,6 +68,7 @@ function mount(overrides: Partial<WorkspaceBrowserProps> = {}) {
     forkSession: vi.fn(),
     renameWorkspace: vi.fn(async () => {}),
     deleteWorkspace: vi.fn(async () => {}),
+    archiveSession: vi.fn(async () => {}),
     insertSessionBefore: vi.fn(async () => {}),
     createWorkspace: vi.fn(async () => workspace('created', [])),
     useDirectoryFlow: bindSnapshotSelector({ getSnapshot: () => true, subscribe: () => () => {} }),
@@ -135,6 +136,50 @@ describe('WorkspaceBrowser', () => {
     expect(screen.queryByText('alpha-s')).toBeNull()
   })
 
+  it('archives a session from the row menu and hides archived rows in both modes', async () => {
+    const archiveSession = vi.fn(async () => {})
+    const b = mount({
+      useSessions: hook(sessionState([summary('kept-s', 2), summary('gone-s', 1)])),
+      useWorkspaces: hook(workspaceState([workspace('alpha', ['kept-s', 'gone-s'])])),
+      archiveSession,
+    })
+    fireEvent.click(screen.getByText('alpha'))
+    fireEvent.click(screen.getByRole('button', { name: '会话“gone-s”的操作' }))
+    fireEvent.click(screen.getByRole('menuitem', { name: '归档会话' }))
+    expect(archiveSession).toHaveBeenCalledWith(sid('gone-s'))
+
+    // The archive-set echo hides the row in grouped mode (count included) and flat mode.
+    rerender(b, { useWorkspaces: hook(workspaceState([workspace('alpha', ['kept-s', 'gone-s'])], new Set([sid('gone-s')]))) })
+    expect(screen.queryByText('gone-s')).toBeNull()
+    expect(screen.getByText('1 个会话')).toBeTruthy()
+    fireEvent.click(screen.getByRole('button', { name: '分组方式' }))
+    fireEvent.click(screen.getByRole('menuitem', { name: '单列表' }))
+    expect(screen.getByText('kept-s')).toBeTruthy()
+    expect(screen.queryByText('gone-s')).toBeNull()
+  })
+
+  it('logs and keeps the tree when the archive call rejects', async () => {
+    const rejection = new Error('archive exploded')
+    const archiveSession = vi.fn(async () => { throw rejection })
+    const warn = vi.spyOn(console, 'warn').mockImplementation(() => {})
+    try {
+      mount({
+        useSessions: hook(sessionState([summary('alpha-s', 1)])),
+        useWorkspaces: hook(workspaceState([workspace('alpha', ['alpha-s'])])),
+        archiveSession,
+      })
+      fireEvent.click(screen.getByText('alpha'))
+      fireEvent.click(screen.getByRole('button', { name: '会话“alpha-s”的操作' }))
+      fireEvent.click(screen.getByRole('menuitem', { name: '归档会话' }))
+      await Promise.resolve()
+      await Promise.resolve()
+      expect(warn).toHaveBeenCalledWith('session archive rejected:', rejection)
+      expect(screen.getByText('alpha-s')).toBeTruthy()
+    } finally {
+      warn.mockRestore()
+    }
+  })
+
   it('renders a fork child as a top-level row without a session twist', () => {
     const parent = summary('parent-s', 2)
     const child = { ...summary('child-s', 1), parentId: parent.id }