fix(sendbox): cancel pending warmup when user submits (#2719)

When a user focuses the input, a 1s timer schedules a
`/api/conversations/{id}/warmup` request as a "pre-warm worker bootstrap"
hint. If the user submits inside that 1s window the timer still fires
later, racing the real `/messages` request on the same conversation.
The backend already single-flights `get_or_build_task`, so the race is
no longer corrupting state, but the extra request is pure waste.

In `sendMessageHandler`, clear any pending warmup timer and mark the
active conversation as already warmed. Covers all submit paths —
normal, side-question, and early-return cases — since the guard runs
before the branch switch.

Author: TCP404

src/renderer/components/chat/sendbox.tsx

@@ -1141,6 +1141,18 @@ const SendBox: React.FC<{
 
   const sendMessageHandler = () => {
     if (isUploading) return;
+    // Cancel any pending warmup: once the user actually submits, the
+    // forthcoming /messages request will build the agent on its own.
+    // Without this, a focus-triggered warmup timer still fires ~1s later
+    // and races the real send over the same conversation.
+    if (warmupTimerRef.current) {
+      clearTimeout(warmupTimerRef.current);
+      warmupTimerRef.current = null;
+    }
+    const activeCid = conversationContext?.conversation_id;
+    if (activeCid) {
+      warmedConversationRef.current = activeCid;
+    }
     if (enableBtw && btwQuestion !== null) {
       const normalizedQuestion = btwQuestion.trim();
       if (!normalizedQuestion) {