feat(lanes,ui): per-lane git surface — Changes panel, VS Code-style diff, branch-aware Add lane, redesigned tooltips (#34, #35)

- Changes card beside lane detail with five modes: Files tree, overview,
  Review (whole diff, per-file collapse), single file, commit history.
- LaneDiffView: unified / side-by-side with independent scroll on both axes
  and mirrored scrollLeft, expand/collapse context, intra-line emphasis.
- Staged-only commit box; git actions (fetch/pull/push/stage/unstage/
  discard/commit/switch/branch-create/branch-delete) guarded in git-ops.js.
- Server: git-diff.js + git-ops.js behind GET /api/lanes/:id/git/* and
  POST /api/lanes/:id/git/:action; gitFacts gains upstream/ahead/behind.
- Add lane: new/existing branch, current branch, worktree list, prefill
  from the git bar's "New lane here"; /api/run/cwds gains a repo kind.
- GlobalTooltip upgrades every native title into a themed anchored bubble;
  chart/info popovers use theme tokens.

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

@@ -109,18 +109,6 @@ 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();
@@ -181,8 +169,101 @@ function savedRouter(over: Record<string, unknown> = {}) {
   };
 }
 
+describe("AddLaneModal — picking an existing branch (issue #34)", () => {
+  const withWorktrees = {
+    branches: ["main", "feat/other", "feat/held"],
+    current: "main",
+    worktrees: [
+      { path: "/Users/tester/projects/repo", branch: "main" },
+      { path: "/lanes/repo__held", branch: "feat/held" },
+    ],
+  };
+
+  it("lists the repo's existing worktrees once the path resolves", async () => {
+    vi.mocked(api.lanes.branches).mockResolvedValue(withWorktrees);
+    renderModal();
+    const user = userEvent.setup();
+
+    const repoField = screen.getByLabelText("Source repository");
+    await focusField(user, repoField);
+    await user.type(repoField, "/Users/tester/projects/repo");
+
+    const panel = await screen.findByTestId("add-lane-worktrees");
+    expect(panel).toHaveTextContent("/lanes/repo__held");
+    expect(panel).toHaveTextContent("feat/held");
+  });
+
+  it("checks an existing branch out, sending no base", async () => {
+    vi.mocked(api.lanes.branches).mockResolvedValue(withWorktrees);
+    vi.mocked(api.lanes.worktree).mockResolvedValue({ lane: laneFixture({ id: 9 }) });
+    renderModal();
+    const user = userEvent.setup();
+
+    const repoField = screen.getByLabelText("Source repository");
+    await focusField(user, repoField);
+    await user.type(repoField, "/Users/tester/projects/repo");
+    await screen.findByLabelText("Branch to fork from");
+    await user.type(screen.getByLabelText("Title"), "Reuse a branch");
+
+    await user.click(screen.getByRole("button", { name: "Existing branch" }));
+    const select = await screen.findByLabelText("Branch to check out");
+    await user.selectOptions(select, "feat/other");
+    await user.click(screen.getByRole("button", { name: "Add lane" }));
+
+    await waitFor(() =>
+      expect(api.lanes.worktree).toHaveBeenCalledWith(
+        expect.objectContaining({ branch: "feat/other", base: undefined })
+      )
+    );
+  });
+
+  it("greys out a branch another worktree already holds", async () => {
+    vi.mocked(api.lanes.branches).mockResolvedValue(withWorktrees);
+    renderModal();
+    const user = userEvent.setup();
+
+    const repoField = screen.getByLabelText("Source repository");
+    await focusField(user, repoField);
+    await user.type(repoField, "/Users/tester/projects/repo");
+    await screen.findByLabelText("Branch to fork from");
+    await user.click(screen.getByRole("button", { name: "Existing branch" }));
+
+    const held = await screen.findByRole("option", { name: /feat\/held/ });
+    expect(held).toBeDisabled();
+    expect(held).toHaveTextContent("/lanes/repo__held");
+    expect(screen.getByRole("option", { name: "feat/other" })).toBeEnabled();
+  });
+
+  it("lets the server name a new branch when the field is left empty", async () => {
+    vi.mocked(api.lanes.branches).mockResolvedValue(withWorktrees);
+    vi.mocked(api.lanes.worktree).mockResolvedValue({ lane: laneFixture({ id: 9 }) });
+    renderModal();
+    const user = userEvent.setup();
+
+    const repoField = screen.getByLabelText("Source repository");
+    await focusField(user, repoField);
+    await user.type(repoField, "/Users/tester/projects/repo");
+    await screen.findByLabelText("Branch to fork from");
+    await user.type(screen.getByLabelText("Title"), "Auto named");
+    // The placeholder previews the name the server will pick.
+    expect(screen.getByLabelText("New branch name")).toHaveAttribute(
+      "placeholder",
+      "feat/auto-named"
+    );
+
+    await user.click(screen.getByRole("button", { name: "Add lane" }));
+    await waitFor(() =>
+      expect(api.lanes.worktree).toHaveBeenCalledWith(
+        expect.objectContaining({ branch: undefined, base: "main" })
+      )
+    );
+  });
+});
+
 describe("AddLaneModal — worktree mode (default)", () => {
-  it("disables confirm until a repo, a title, a resolved branch list, and a new branch name are all present", () => {
+  // The branch NAME is no longer part of this list: an empty one means "let
+  // the server name it" (issue #34).
+  it("disables confirm until a repo, a title and a resolved branch list are all present", () => {
     renderModal();
     expect(screen.getByRole("button", { name: "Add lane" })).toBeDisabled();
   });
@@ -191,6 +272,7 @@ describe("AddLaneModal — worktree mode (default)", () => {
     vi.mocked(api.lanes.branches).mockResolvedValue({
       branches: ["main", "feat/other"],
       current: "main",
+      worktrees: [],
     });
     renderModal();
     const user = userEvent.setup();
@@ -223,7 +305,11 @@ describe("AddLaneModal — worktree mode (default)", () => {
   });
 
   it("submits through the worktree provisioning endpoint, with the typed branch name", async () => {
-    vi.mocked(api.lanes.branches).mockResolvedValue({ branches: ["main"], current: "main" });
+    vi.mocked(api.lanes.branches).mockResolvedValue({
+      branches: ["main"],
+      current: "main",
+      worktrees: [],
+    });
     vi.mocked(api.lanes.worktree).mockResolvedValue({ lane: laneFixture({ id: 9 }) });
     const onAdded = vi.fn();
     const onClose = vi.fn();
@@ -239,7 +325,6 @@ describe("AddLaneModal — worktree mode (default)", () => {
         title: "New feature",
         base: "main",
         branch: "feat/new-feature",
-        pipeline: "default",
         tool: "claude",
       });
     });
@@ -253,7 +338,11 @@ describe("AddLaneModal — worktree mode (default)", () => {
   });
 
   it("shows a server error and leaves the modal open instead of closing silently", async () => {
-    vi.mocked(api.lanes.branches).mockResolvedValue({ branches: ["main"], current: "main" });
+    vi.mocked(api.lanes.branches).mockResolvedValue({
+      branches: ["main"],
+      current: "main",
+      worktrees: [],
+    });
     vi.mocked(api.lanes.worktree).mockRejectedValue(new Error("EWORKTREEDIRCOLLISION"));
     const onClose = vi.fn();
     renderModal({ onClose });
@@ -272,7 +361,11 @@ describe("AddLaneModal — worktree mode (default)", () => {
   });
 
   it("fires profileInit, agentsInstall, and mcpSync after a successful worktree call", async () => {
-    vi.mocked(api.lanes.branches).mockResolvedValue({ branches: ["main"], current: "main" });
+    vi.mocked(api.lanes.branches).mockResolvedValue({
+      branches: ["main"],
+      current: "main",
+      worktrees: [],
+    });
     vi.mocked(api.lanes.worktree).mockResolvedValue({
       lane: { id: 42, title: "demo", cwd: "/lanes/demo", status: "provisioning" } as Lane,
     });
@@ -291,7 +384,11 @@ describe("AddLaneModal — worktree mode (default)", () => {
   });
 
   it("still calls onAdded even when every setup call fails", async () => {
-    vi.mocked(api.lanes.branches).mockResolvedValue({ branches: ["main"], current: "main" });
+    vi.mocked(api.lanes.branches).mockResolvedValue({
+      branches: ["main"],
+      current: "main",
+      worktrees: [],
+    });
     vi.mocked(api.lanes.worktree).mockResolvedValue({
       lane: { id: 43, title: "demo2", cwd: "/lanes/demo2", status: "provisioning" } as Lane,
     });
@@ -311,7 +408,11 @@ describe("AddLaneModal — worktree mode (default)", () => {
   });
 
   it("keeps the summary up when a setup step FAILED, and closes on the button that replaces Add lane", async () => {
-    vi.mocked(api.lanes.branches).mockResolvedValue({ branches: ["main"], current: "main" });
+    vi.mocked(api.lanes.branches).mockResolvedValue({
+      branches: ["main"],
+      current: "main",
+      worktrees: [],
+    });
     vi.mocked(api.lanes.worktree).mockResolvedValue({
       lane: { id: 44, title: "demo3", cwd: "/lanes/demo3", status: "provisioning" } as Lane,
     });
@@ -334,7 +435,11 @@ describe("AddLaneModal — worktree mode (default)", () => {
   });
 
   it("waits for the background worktree provisioning to finish before running setup, and skips setup if it fails", async () => {
-    vi.mocked(api.lanes.branches).mockResolvedValue({ branches: ["main"], current: "main" });
+    vi.mocked(api.lanes.branches).mockResolvedValue({
+      branches: ["main"],
+      current: "main",
+      worktrees: [],
+    });
     vi.mocked(api.lanes.worktree).mockResolvedValue({
       lane: { id: 45, title: "demo4", cwd: "/lanes/demo4", status: "provisioning" } as Lane,
     });
@@ -397,7 +502,6 @@ describe("AddLaneModal — repo mode (adopt)", () => {
       expect(api.lanes.ensure).toHaveBeenCalledWith({
         cwd: "/Users/tester/projects/repo",
         title: "main repo",
-        pipeline: "default",
         tool: "claude",
       })
     );
@@ -591,50 +695,6 @@ describe("AddLaneModal — a router profile that disappeared", () => {
   });
 });
 
-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();
-  });
-});
-
 describe("AddLaneModal — tool selection", () => {
   it("sends the picked tool when adopting a repo", async () => {
     vi.mocked(api.lanes.ensure).mockResolvedValue({
@@ -679,3 +739,41 @@ describe("AddLaneModal — tool selection", () => {
     );
   });
 });
+
+describe("AddLaneModal — working straight on main (no worktree)", () => {
+  beforeEach(() => {
+    vi.mocked(api.lanes.branches).mockResolvedValue({
+      branches: ["development", "main"],
+      current: "development",
+      worktrees: [],
+    });
+  });
+
+  it("jumps to Repo mode from the branch choice", async () => {
+    const user = userEvent.setup();
+    renderModal();
+    const repoField = screen.getByLabelText("Source repository");
+    await focusField(user, repoField);
+    await user.type(repoField, "/Users/tester/projects/repo");
+    await screen.findByTestId("add-lane-branch-section");
+
+    await user.click(screen.getByRole("button", { name: "Current branch" }));
+
+    // Repo mode adopts the directory as it stands — no branch section left to
+    // answer, because there is no fork to configure.
+    expect(screen.queryByTestId("add-lane-branch-section")).toBeNull();
+    expect(screen.getByRole("button", { name: "Repo" })).toHaveAttribute("aria-pressed", "true");
+  });
+
+  it("prefills the repo and branch it was opened with", async () => {
+    renderModal({
+      prefill: { sourceRepo: "/Users/tester/projects/repo", branch: "development" },
+    });
+    expect(await screen.findByTestId("add-lane-branch-section")).toBeInTheDocument();
+    expect(screen.getByLabelText("Source repository")).toHaveValue("/Users/tester/projects/repo");
+    expect(screen.getByRole("button", { name: "Existing branch" })).toHaveAttribute(
+      "aria-pressed",
+      "true"
+    );
+  });
+});