feat(sagi): spawn a real claude session for Sagi's Ask handoff

Unmatched Ask questions now adopt a dedicated "Sagi" lane (POST
/api/lanes/ensure, cwd defaults to $HOME) and spawn a tmux-backed claude
run there instead of just prefilling the Run page composer.

client/src/components/Sagi/Sagi.tsx

@@ -78,6 +78,7 @@ import { useSagiBrain } from "./useSagiBrain";
 import { useSagiPosition, SAGI_SIZE } from "./useSagiPosition";
 import { matchIntent } from "./intents";
 import { sagiPrefs } from "./prefs";
+import { api } from "../../lib/api";
 import "./sagi.css";
 
 const FLYOUT_GAP = 10; // px between avatar and flyout
@@ -196,11 +197,31 @@ export function Sagi() {
     (query: string): string | null => {
       const result = matchIntent(query, brain.status);
       if (result.kind === "answer") return result.text;
-      // Handoff: spawn a real claude via the existing Run page. `autostart=1`
-      // tells Run to fire the prompt automatically once it's prefilled, so the
-      // question is actually sent instead of just dropped into the composer.
-      navigate(`/run?prompt=${encodeURIComponent(result.prompt)}&autostart=1`);
-      setOpen(false);
+      // Handoff: ensure the "Sagi" lane exists for this dashboard, spawn a
+      // fresh claude session in it carrying the user's prompt as its first
+      // message, then jump to the Run page so the live pane is observable.
+      // Fire-and-forget — the panel already clears its composer on null and
+      // closes; errors surface as an answer instead of silently swallowing.
+      const prompt = result.prompt;
+      brain.setThinking(true);
+      (async () => {
+        try {
+          const { lane } = await api.lanes.ensure({ title: "Sagi" });
+          await api.run.start({
+            laneId: lane.id,
+            cwd: lane.cwd,
+            initialPrompt: prompt,
+            permissionMode: "acceptEdits",
+          });
+          navigate(`/run?laneId=${lane.id}&autostart=1`);
+          setOpen(false);
+        } catch (err) {
+          const msg = err instanceof Error ? err.message : String(err);
+          brain.setBubble(`couldn't start that session: ${msg}`);
+        } finally {
+          brain.setThinking(false);
+        }
+      })();
       return null;
     },
     [brain, navigate]

client/src/components/Sagi/useSagiBrain.ts

@@ -87,6 +87,10 @@ export interface SagiBrain {
   status: SagiStatus;
   bubble: string | null;
   dismissBubble: () => void;
+  /** Imperative bubble setter for one-off messages from the shell (e.g. spawn
+   *  errors). Bypasses the throttle because the caller decided this message
+   *  must be seen right now. Auto-clears after the standard bubble TTL. */
+  setBubble: (text: string) => void;
   muted: boolean;
   toggleMute: () => void;
   clearAlerts: () => void;
@@ -103,7 +107,7 @@ export function useSagiBrain(): SagiBrain {
     connected: true,
   }));
   const [tick, setTick] = useState(now0);
-  const [bubble, setBubble] = useState<string | null>(null);
+  const [bubble, setBubbleState] = useState<string | null>(null);
   const [muted, setMuted] = useState<boolean>(() => sagiPrefs.getMuted());
 
   const bubbleTimer = useRef<ReturnType<typeof setTimeout>>();
@@ -121,8 +125,8 @@ export function useSagiBrain(): SagiBrain {
     if (!force && t - lastBubbleAt.current < BUBBLE_THROTTLE_MS) return;
     lastBubbleAt.current = t;
     clearTimeout(bubbleTimer.current);
-    setBubble(text);
-    bubbleTimer.current = setTimeout(() => setBubble(null), BUBBLE_MS);
+    setBubbleState(text);
+    bubbleTimer.current = setTimeout(() => setBubbleState(null), BUBBLE_MS);
   }, []);
 
   // Seed from the REST snapshot on mount so counts are accurate immediately -
@@ -176,7 +180,7 @@ export function useSagiBrain(): SagiBrain {
 
   const dismissBubble = useCallback(() => {
     clearTimeout(bubbleTimer.current);
-    setBubble(null);
+    setBubbleState(null);
   }, []);
 
   const toggleMute = useCallback(() => {
@@ -193,5 +197,25 @@ export function useSagiBrain(): SagiBrain {
     []
   );
 
-  return { mood, status, bubble, dismissBubble, muted, toggleMute, clearAlerts, setThinking };
+  // One-shot bubble: clears itself after BUBBLE_MS. Used by the shell for
+  // imperative messages (e.g. spawn errors) that must appear now and fade,
+  // bypassing the throttled mood-driven showBubble path.
+  const setBubble = useCallback((text: string) => {
+    if (!text) return;
+    clearTimeout(bubbleTimer.current);
+    setBubbleState(text);
+    bubbleTimer.current = setTimeout(() => setBubbleState(null), BUBBLE_MS);
+  }, []);
+
+  return {
+    mood,
+    status,
+    bubble,
+    dismissBubble,
+    setBubble,
+    muted,
+    toggleMute,
+    clearAlerts,
+    setThinking,
+  };
 }

client/src/lib/api.ts

@@ -1832,10 +1832,12 @@ export const api = {
     list: () => request<{ lanes: Lane[]; counts: LaneCounts }>("/lanes"),
     /**
      * POST /api/lanes/ensure — ensure a lane exists for the given cwd.
-     * @param body The cwd and optional title.
+     * @param body The cwd and optional title. When `cwd` is omitted the server
+     *   falls back to the user's home directory — useful for lanes whose
+     *   location isn't tied to a specific project (e.g. Sagi's mascot lane).
      * @returns `{ lane, created }` — the lane (newly created or existing) and whether it was created.
      */
-    ensure: (body: { cwd: string; title?: string; pipeline?: string }) =>
+    ensure: (body: { cwd?: string; title?: string; pipeline?: string }) =>
       request<{ lane: Lane; created: boolean }>("/lanes/ensure", {
         method: "POST",
         body: JSON.stringify(body),