Fix pre-stream gap UX: thinking dots + stop button on send

static/boot.js

@@ -1,6 +1,6 @@
 async function cancelStream(){
   const streamId = S.activeStreamId;
-  if(!streamId){if(typeof _abortPendingChatStart==='function')_abortPendingChatStart();if(S.busy)setBusy(false);return;}
+  if(!streamId){window._abortPendingChatStart?.();if(S.busy){setBusy(false);if(typeof removeThinking==='function')removeThinking();}return;}
   try{
     await fetch(new URL(`api/chat/cancel?stream_id=${encodeURIComponent(streamId)}`,document.baseURI||location.href).href,{credentials:'include'});
   }catch(e){/* cancel request failed - cleanup below still runs */}

static/ui.js

@@ -6334,11 +6334,8 @@ function finalizeThinkingCard(){
   }
 }
 function appendThinking(text=''){
-  // Guard: ignore if session was switched during an async SSE stream.
-  // The old stream's reasoning events can still fire after switch;
-  // without this check they would pollute the new session's DOM.
+  // Guard: ignore if no active session (e.g. switched away before stream start).
   if(!S.session) return;
-  if(!S.activeStreamId) return;
   $('emptyState').style.display='none';
   let turn=$('liveAssistantTurn');
   if(!turn){