fix(lanes): wait for worktree provisioning before auto-setup

POST /worktree answers with 202 before the background git worktree
add finishes, so profileInit/agentsInstall/mcpSync were racing the
lane's own directory into existence and mostly failing. Poll
GET /api/lanes/:id until provisioning leaves "provisioning" first.

client/src/components/lanes/AddLaneModal.tsx

@@ -5,9 +5,10 @@
  * dashboard provisions a managed git worktree via `POST /api/lanes/worktree`
  * — the dashboard invents the lane's own directory and branch name, the same
  * way Shipyard's "+ Add lane" never asks a human to name a folder. The lane
- * returned is `status: "provisioning"`; the existing `lane_update` WebSocket
- * subscription in the Workspace page flips it to idle when the worktree is
- * actually ready, so this component does not poll.
+ * returned is `status: "provisioning"`: 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.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
@@ -19,6 +20,22 @@ import { api } from "../../lib/api";
 import type { CwdSuggestion } from "../../lib/api";
 import type { Lane } from "../../lib/types";
 
+/** Polls the lane until the background `git worktree add` finishes (status
+ *  leaves "provisioning"), or gives up after `timeoutMs`. Returns the final
+ *  lane record, or `null` on timeout. */
+async function waitForProvisioned(
+  laneId: number,
+  { intervalMs = 500, timeoutMs = 30000 } = {}
+): Promise<Lane | null> {
+  const deadline = Date.now() + timeoutMs;
+  for (;;) {
+    const { lane } = await api.lanes.get(laneId);
+    if (lane.status !== "provisioning") return lane;
+    if (Date.now() >= deadline) return null;
+    await new Promise((r) => window.setTimeout(r, intervalMs));
+  }
+}
+
 export function AddLaneModal({
   open,
   onClose,
@@ -102,6 +119,19 @@ export function AddLaneModal({
         title: name,
         base: base || undefined,
       });
+      onAdded(result.lane);
+
+      // POST /worktree returns as soon as the DB row exists (202) — the
+      // actual `git worktree add` runs afterward, in the background, on the
+      // server. Firing setup against the lane's cwd before that finishes
+      // means agents/mcp write into a directory that doesn't exist yet, so
+      // wait for provisioning to leave the "provisioning" status first.
+      const provisionedLane = await waitForProvisioned(result.lane.id);
+      if (!provisionedLane || provisionedLane.status === "failed") {
+        setBusy(false);
+        setError(t("addLaneProvisionFailed"));
+        return;
+      }
 
       const [profileOutcome, agentsOutcome, mcpOutcome] = await Promise.allSettled([
         api.lanes.profileInit(result.lane.id),
@@ -132,7 +162,6 @@ export function AddLaneModal({
       // user dismisses it themselves (Cancel/X) once they've seen it, rather
       // than racing a timer that can close before they've looked at it.
       setBusy(false);
-      onAdded(result.lane);
     } catch (err) {
       setError(err instanceof Error ? err.message : String(err));
       setBusy(false);