feat(lanes): let Add Lane choose the pipeline template

Creation is the only point the UI could ever set a lane's template, and it
never offered the choice — so every lane added from "+ Add lane" was born
on `default` and rendered an 8-node map for a 16-node workflow, with no
screen able to change it afterwards. That is the defect that made the
ship-feature template unreachable from the browser.

The modal now shows a *Pipeline template* select fed by
`GET /api/lanes/pipelines`, labelled with each template's node count so the
consequence of the choice is visible. A failed fetch degrades to a `default`
option rather than blocking lane creation.

`pipeline` was already accepted by `POST /api/lanes` but silently dropped by
`/ensure` and `/worktree`, which build their own createLane payloads; both
now pass it through, and both map `EBADPIPELINE` to 400 like `EBADCWD`.

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

@@ -21,6 +21,7 @@ vi.mock("../../../lib/api", () => ({
   api: {
     lanes: {
       branches: vi.fn(),
+      pipelines: vi.fn(),
       worktree: vi.fn(),
       ensure: vi.fn(),
       browse: vi.fn(),
@@ -101,6 +102,18 @@ async function fillWorktreeForm(
 
 beforeEach(() => {
   vi.mocked(api.lanes.branches).mockReset();
+  vi.mocked(api.lanes.pipelines)
+    .mockReset()
+    .mockResolvedValue({
+      pipelines: [
+        { id: "default", name: "Default feature pipeline", nodes: new Array(8).fill({ id: "n" }) },
+        {
+          id: "ship-feature",
+          name: "Ship feature (lane pipeline)",
+          nodes: new Array(16).fill({ id: "n" }),
+        },
+      ],
+    });
   vi.mocked(api.lanes.worktree).mockReset();
   vi.mocked(api.lanes.ensure).mockReset();
   vi.mocked(api.lanes.browse).mockReset();
@@ -174,6 +187,7 @@ describe("AddLaneModal — worktree mode (default)", () => {
         title: "New feature",
         base: "main",
         branch: "feat/new-feature",
+        pipeline: "default",
       });
     });
     expect(onAdded).toHaveBeenCalledWith(
@@ -327,6 +341,7 @@ describe("AddLaneModal — repo mode (adopt)", () => {
       expect(api.lanes.ensure).toHaveBeenCalledWith({
         cwd: "/Users/tester/projects/repo",
         title: "main repo",
+        pipeline: "default",
       })
     );
     expect(api.lanes.worktree).not.toHaveBeenCalled();
@@ -376,3 +391,47 @@ describe("AddLaneModal — folder browse", () => {
     expect(onClose).not.toHaveBeenCalled();
   });
 });
+
+describe("AddLaneModal — pipeline template", () => {
+  it("offers every template the server reports and sends the chosen one when adopting a repo", async () => {
+    // Creation is the ONLY point the UI can set a template, so a lane born on
+    // `default` renders 8 nodes for a 16-node workflow with no way back from
+    // any screen.
+    vi.mocked(api.lanes.ensure).mockResolvedValue({
+      lane: laneFixture({ status: "idle" }),
+      created: true,
+    });
+    renderModal();
+    const user = userEvent.setup();
+
+    await user.click(screen.getByRole("button", { name: "Repo" }));
+    const select = await screen.findByLabelText("Pipeline template");
+    await waitFor(() =>
+      expect(screen.getByRole("option", { name: /Ship feature/ })).toBeInTheDocument()
+    );
+    expect(
+      screen.getByRole("option", { name: /Default feature pipeline \(8\)/ })
+    ).toBeInTheDocument();
+
+    const repoField = screen.getByLabelText("Directory");
+    await focusField(user, repoField);
+    await user.type(repoField, "/Users/tester/projects/repo");
+    await user.selectOptions(select, "ship-feature");
+    await user.click(screen.getByRole("button", { name: "Add lane" }));
+
+    await waitFor(() =>
+      expect(api.lanes.ensure).toHaveBeenCalledWith(
+        expect.objectContaining({ pipeline: "ship-feature" })
+      )
+    );
+  });
+
+  it("still renders a usable select, and still creates the lane, when the template list cannot be fetched", async () => {
+    vi.mocked(api.lanes.pipelines).mockRejectedValue(new Error("offline"));
+    renderModal();
+
+    const select = await screen.findByLabelText("Pipeline template");
+    await waitFor(() => expect(select).toHaveValue("default"));
+    expect(screen.getByRole("option", { name: "default" })).toBeInTheDocument();
+  });
+});