feat(ui): a Claude-Desktop-style home for every workspace

/workspace?lane=<id> opens on the workspace's home (WorkspaceHome): a prompt
box whose Start opens a new session in the first free pane slot, Recents (a
live session attaches its pane, any other opens its transcript, nothing
resumes), and Instructions / Memory / Context / Folder. Instructions live in
lanes.instructions, extra folders and uploaded files in the new lane_sources
table (copies under <data dir>/workspace-context/<lane id>/); spawnRun reads
them from the lane's rows and hands Claude --add-dir + an appended system
prompt file, Codex --add-dir + developer_instructions. Memory is read-only.

Every dashboard pane carries AGENTHUB_RUN_ID; hooks forward it and the run
records which session the pane holds (a Claude pane follows /clear and
/resume but not a nested claude -p), so the sidebar and notifications open
the right pane (&run=). Settings loses its Projects group; Worktrees now
decides which worktrees Add folder suggests.

client/src/components/run/__tests__/LaneConsolePane.test.tsx

@@ -556,4 +556,50 @@ describe("LaneConsolePane", () => {
     expect(api.lanes.action).not.toHaveBeenCalled();
     expect(api.run.start).not.toHaveBeenCalled();
   });
+
+  it("attaches once the lane arrives on a cold load, and ignores another lane's run", async () => {
+    vi.mocked(api.run.get).mockResolvedValue({
+      id: "agenthub-lane-1-1",
+      laneId: 1,
+      slot: 1,
+      status: "running",
+      cwd: "/workspace/a",
+      model: null,
+      permissionMode: null,
+      effort: null,
+      resumeSessionId: null,
+      sessionId: "s-9",
+      startedAt: null,
+      promptPreview: null,
+      tool: "claude",
+    });
+    const req = { runId: "agenthub-lane-1-1", nonce: "k2" };
+    const { rerender } = render(
+      <MemoryRouter>
+        <LaneConsolePane {...baseProps()} laneId={null} attachRequest={req} />
+      </MemoryRouter>
+    );
+    // The lane list lands only after the pane mounted (and after any early
+    // attach would have resolved) — the switch effect must not win.
+    await new Promise((r) => setTimeout(r, 20));
+    rerender(
+      <MemoryRouter>
+        <LaneConsolePane {...baseProps()} attachRequest={req} />
+      </MemoryRouter>
+    );
+    await screen.findByTestId("terminal-view");
+    expect(api.run.get).toHaveBeenCalledWith("agenthub-lane-1-1");
+
+    vi.mocked(api.run.get).mockClear();
+    rerender(
+      <MemoryRouter>
+        <LaneConsolePane
+          {...baseProps()}
+          attachRequest={{ runId: "agenthub-lane-12", nonce: "k3" }}
+        />
+      </MemoryRouter>
+    );
+    await new Promise((r) => setTimeout(r, 10));
+    expect(api.run.get).not.toHaveBeenCalled();
+  });
 });