fix(composer): preserve send-button sync under scheduled resize (#4042)

static/boot.js

@@ -1288,6 +1288,7 @@ $('modelSelect').onchange=async()=>{
   }
 };
 $('msg').addEventListener('input',()=>{
+  updateSendBtn();
   scheduleComposerAutoResize();
   // Persist composer draft to server (debounced in _saveComposerDraft).
   const sid = S && S.session && S.session.session_id;

static/messages.js

@@ -3869,9 +3869,17 @@ function transcript(){
 }
 
 let _composerAutoResizeRaf=0;
-function autoResize(){const el=$('msg');el.style.height='auto';el.style.height=Math.min(el.scrollHeight,200)+'px';updateSendBtn();}
-function scheduleComposerAutoResize(){
+function autoResize(){
+  if(_composerAutoResizeRaf && typeof cancelAnimationFrame==='function'){
+    cancelAnimationFrame(_composerAutoResizeRaf);
+    _composerAutoResizeRaf=0;
+  }
+  const el=$('msg');
+  el.style.height='auto';
+  el.style.height=Math.min(el.scrollHeight,200)+'px';
   updateSendBtn();
+}
+function scheduleComposerAutoResize(){
   if(typeof requestAnimationFrame!=='function'){autoResize();return;}
   if(_composerAutoResizeRaf) return;
   _composerAutoResizeRaf=requestAnimationFrame(()=>{