chore: v2.8.12 — clone queue and progress, session defaults, chat agents, drops as @ mentions

Whole tree from parallel sessions, plus the version bump:
- Clone: a queue with live progress (Add workspace and extra folders),
  clones run under nice/ionice so the machine stays responsive.
- Settings → AI tools → Session defaults: a new session's default
  permission mode / bypass per account.
- Chat lists the background subagents that have not reported back yet.
- A file pasted or dropped into a claude pane goes in as an @ mention.
- Changes panel: say why amend/undo is refused on a pushed commit.
- openapi.yaml regenerated (Artifacts, Host, resumeById).

client/src/components/lanes/__tests__/LaneChangesPanel.test.tsx

@@ -1062,6 +1062,20 @@ describe("LaneChangesPanel", () => {
       );
     });
 
+    it("does not offer Undo for a top commit its upstream already holds", async () => {
+      withParent();
+      vi.mocked(api.lanes.git).mockResolvedValue(
+        facts({ hasRemote: true, upstream: "origin/feat/thing", ahead: 0, behind: 0 })
+      );
+      const user = userEvent.setup();
+      render(<LaneChangesPanel laneId={7} />);
+      await screen.findByTestId("lane-changes-overview");
+      await user.click(screen.getByRole("button", { name: "History" }));
+      const undo = within(await commitMenu(user)).getByTestId("lane-changes-menu-undo-commit");
+      await waitFor(() => expect(undo).toBeDisabled());
+      expect(undo).toHaveAttribute("title", expect.stringMatching(/already on the remote/));
+    });
+
     it("cherry-picks only from another branch's history", async () => {
       withParent();
       vi.mocked(api.lanes.git).mockResolvedValue(facts());