feat(lanes): offer a create/update readme run when adding a lane

An optional checkbox in the Add-lane modal starts the new lane's terminal
run right after creation with `/sg-all:sg-md-writing` as its first message,
so the lane opens already writing or refreshing its CLAUDE.md/AGENTS.md set.
Claude lanes only — codex has no slash commands.

client/src/components/lanes/AddLaneModal.tsx

@@ -14,6 +14,8 @@
  * the route answers before the actual `git worktree add` runs, so this
  * component polls `GET /api/lanes/:id` until that finishes before running the
  * auto-setup calls against a cwd that must actually exist on disk first.
+ * An optional "Create/update readme file" checkbox starts the lane's terminal
+ * run right after creation with `/sg-all:sg-md-writing` as its first message.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
@@ -94,6 +96,7 @@ export function AddLaneModal({
   const [branches, setBranches] = useState<string[] | null>(null);
   const [base, setBase] = useState("");
   const [pipeline, setPipeline] = useState("default");
+  const [writeDocs, setWriteDocs] = useState(false);
   const [pipelines, setPipelines] = useState<{ id: string; name: string; nodes: unknown[] }[]>([]);
   const [branchesError, setBranchesError] = useState<string | null>(null);
   const [tool, setTool] = useState<LaneTool>("claude");
@@ -114,6 +117,7 @@ export function AddLaneModal({
     setBranches(null);
     setBase("");
     setPipeline("default");
+    setWriteDocs(false);
     setTool("claude");
     setBranchesError(null);
     setError(null);
@@ -177,6 +181,14 @@ export function AddLaneModal({
     return () => window.clearTimeout(timer);
   }, [mode, sourceRepo, t]);
 
+  // The checkbox below runs the docs skill by opening the lane's own terminal
+  // run with the slash command as its first message — a skill only exists
+  // inside a CLI session, so there is nothing server-side to call instead.
+  // Claude-only: codex has no slash commands (same reason LaneConsolePane
+  // prefills prose for a codex lane).
+  const startDocsRun = (laneId: number, cwd: string) =>
+    api.run.start({ laneId, cwd, initialPrompt: "/sg-all:sg-md-writing" });
+
   const submit = async () => {
     const repo = sourceRepo.trim();
     const name = title.trim();
@@ -192,6 +204,7 @@ export function AddLaneModal({
           pipeline,
           tool,
         });
+        if (writeDocs && tool === "claude") await startDocsRun(result.lane.id, result.lane.cwd);
         onAdded(result.lane);
         reset();
         onClose();
@@ -242,6 +255,10 @@ export function AddLaneModal({
         mcp: mcpOutcome.status === "fulfilled" ? "ok" : "failed",
       });
 
+      if (writeDocs && tool === "claude") {
+        await startDocsRun(result.lane.id, provisionedLane.cwd);
+      }
+
       if (import.meta.env.DEV) {
         console.info("[add-lane] auto-setup result:", {
           profile:
@@ -390,6 +407,21 @@ export function AddLaneModal({
           <p className="mt-1 text-[10px] text-fg-muted">{t("addLanePipelineHint")}</p>
         </div>
 
+        {tool === "claude" && (
+          <div>
+            <label className="flex items-center gap-2 text-xs text-fg-secondary">
+              <input
+                type="checkbox"
+                checked={writeDocs}
+                onChange={(e) => setWriteDocs(e.target.checked)}
+                className="h-3.5 w-3.5 accent-accent"
+              />
+              {t("addLaneWriteDocsLabel")}
+            </label>
+            <p className="mt-1 text-[10px] text-fg-muted">{t("addLaneWriteDocsHint")}</p>
+          </div>
+        )}
+
         {mode === "worktree" && branches && (
           <div>
             <label className="mb-1 block text-xs text-fg-secondary" htmlFor="add-lane-base">

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

@@ -30,6 +30,7 @@ vi.mock("../../../lib/api", () => ({
       agentsInstall: vi.fn(),
       mcpSync: vi.fn(),
     },
+    run: { start: vi.fn() },
   },
 }));
 
@@ -398,6 +399,42 @@ describe("AddLaneModal — folder browse", () => {
   });
 });
 
+describe("AddLaneModal — create/update readme", () => {
+  it("opens the new lane's terminal on the docs skill only when the box is ticked", async () => {
+    vi.mocked(api.run.start)
+      .mockReset()
+      .mockResolvedValue({} as never);
+    vi.mocked(api.lanes.ensure).mockResolvedValue({
+      lane: laneFixture({ status: "idle", cwd: "/Users/tester/projects/repo" }),
+      created: true,
+    });
+    renderModal();
+    const user = userEvent.setup();
+
+    await user.click(screen.getByRole("button", { name: "Repo" }));
+    const repoField = screen.getByLabelText("Directory");
+    await focusField(user, repoField);
+    await user.type(repoField, "/Users/tester/projects/repo");
+    await user.click(screen.getByLabelText("Create/update readme file"));
+    await user.click(screen.getByRole("button", { name: "Add lane" }));
+
+    await waitFor(() =>
+      expect(api.run.start).toHaveBeenCalledWith({
+        laneId: 9,
+        cwd: "/Users/tester/projects/repo",
+        initialPrompt: "/sg-all:sg-md-writing",
+      })
+    );
+  });
+
+  it("is hidden for a codex lane, which has no slash commands", async () => {
+    renderModal();
+    const user = userEvent.setup();
+    await user.click(screen.getByRole("button", { name: "Codex" }));
+    expect(screen.queryByLabelText("Create/update readme file")).toBeNull();
+  });
+});
+
 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