fix(web): harden typed SPA chat lifecycle

Co-Authored-By: Claude Haiku 4.5 <[email protected]>

apps/web/src/spa/chat/composer.tsx

@@ -4,6 +4,10 @@ interface ComposerProps {
   onSend: (input: { content: string; provider?: string; modelId?: string }) => void;
   onStop: () => void;
   streaming: boolean;
+  /** True from local send time through server turn startup/ack and
+   * throughout streaming — a superset of `streaming` that also covers the
+   * pre-ack window where a second send could otherwise slip through. */
+  sending: boolean;
   hasConversation: boolean;
 }
 
@@ -11,14 +15,16 @@ export function Composer({
   onSend,
   onStop,
   streaming,
+  sending,
   hasConversation,
 }: ComposerProps): ReactElement {
   const [content, setContent] = useState('');
   const [provider, setProvider] = useState('');
   const [modelId, setModelId] = useState('');
+  const busy = streaming || sending;
 
   function submit(): void {
-    if (streaming) return;
+    if (busy) return;
     const trimmed = content.trim();
     if (!trimmed) return;
     onSend({
@@ -72,7 +78,7 @@ export function Composer({
         />
         <button
           type="submit"
-          disabled={!content.trim() || streaming}
+          disabled={!content.trim() || busy}
           className="rounded px-3 py-2 text-sm font-medium"
         >
           Send