feat: harden runtime readiness and session workflow

frontend/src/shell/SteerInput.tsx

@@ -15,13 +15,24 @@ interface Props {
   sessionId: string | null;
   /** Called with the new session id when the box starts a fresh session. */
   onSessionCreated?: (id: string) => void;
+  /** Paint the provisional session view before the create request completes. */
+  onSessionCreating?: (question: string) => void;
+  /** Revert the provisional view when session creation fails. */
+  onSessionCreateFailed?: () => void;
   /** Interrupt the running session, persisting its state. */
   onStop?: () => void;
   /** Lets the parent focus the composer (e.g. on "New session"). */
   inputRef?: React.Ref<HTMLTextAreaElement>;
 }
 
-export function SteerInput({ sessionId, onSessionCreated, onStop, inputRef }: Props) {
+export function SteerInput({
+  sessionId,
+  onSessionCreated,
+  onSessionCreating,
+  onSessionCreateFailed,
+  onStop,
+  inputRef,
+}: Props) {
   const [text, setText] = useState("");
   const [busy, setBusy] = useState(false);
   const setLastUserEntry = useSessionStore((s) => s.setLastUserEntry);
@@ -48,16 +59,29 @@ export function SteerInput({ sessionId, onSessionCreated, onStop, inputRef }: Pr
     const trimmed = text.trim();
     if (!trimmed || busy) return;
     setBusy(true);
-    try {
-      if (sessionId) {
+    if (sessionId) {
+      try {
         await postSteer(sessionId, trimmed);
-      } else {
-        const { id } = await createSession({ question: trimmed });
-        setPhase("F1"); // optimistic: paint F1 yellow during the cold start, before the first gate
-        onSessionCreated?.(id);
+        setLastUserEntry({ kind: "input", text: trimmed });
+        setText("");
+      } finally {
+        setBusy(false);
       }
-      setLastUserEntry({ kind: "input", text: trimmed });
+      return;
+    }
+
+    // Session creation can include cold-start work. Hand the UI state to the
+    // provisional session view before awaiting it so feedback is immediate.
+    setPhase("F1");
+    setLastUserEntry({ kind: "input", text: trimmed });
+    onSessionCreating?.(trimmed);
+    try {
+      const { id } = await createSession({ question: trimmed });
+      onSessionCreated?.(id);
       setText("");
+    } catch {
+      // Keep the question in the composer so retrying does not require retyping.
+      onSessionCreateFailed?.();
     } finally {
       setBusy(false);
     }
@@ -92,7 +116,8 @@ export function SteerInput({ sessionId, onSessionCreated, onStop, inputRef }: Pr
         onKeyDown={handleKeyDown}
         placeholder={sessionId ? "Free steering (!)…" : "Ask a question to start a new session…"}
         aria-label={sessionId ? "Steering" : "New question"}
-        className="max-h-40 flex-1 resize-none bg-transparent px-1 py-1 text-sm leading-relaxed outline-none placeholder:text-muted-foreground"
+        data-awaiting-input={sessionId ? undefined : "true"}
+        className={["max-h-40 flex-1 resize-none rounded-lg px-1 py-1 text-sm leading-relaxed outline-none placeholder:text-muted-foreground", sessionId ? "bg-transparent" : "thot-awaiting-input"].join(" ")}
       />
       <button
         type="button"