diff --git a/chat/templates/chat.html b/chat/templates/chat.html
index 8833062..c2f622c 100644
--- a/chat/templates/chat.html
+++ b/chat/templates/chat.html
@@ -78,7 +78,11 @@ document.querySelector('.drawer-toggle')?.addEventListener('click', (e) => {
   function unlock() {
     isStreaming = false;
     if (sendBtn) sendBtn.disabled = false;
-    if (textarea) textarea.disabled = false;
+    if (textarea) {
+      textarea.readOnly = false;
+      textarea.value = '';
+      textarea.focus();
+    }
     const stop = shell.querySelector('.stop-streaming');
     if (stop) stop.remove();
   }
@@ -128,7 +132,10 @@ document.querySelector('.drawer-toggle')?.addEventListener('click', (e) => {
   form.addEventListener('submit', () => {
     isStreaming = true;
     if (sendBtn) sendBtn.disabled = true;
-    if (textarea) textarea.disabled = true;
+    // readOnly (not disabled) — disabled fields are excluded from the
+    // form submission, which would send prose="" and trigger the
+    // server's empty-prose 400.
+    if (textarea) textarea.readOnly = true;
     if (!shell.querySelector('.stop-streaming')) {
       const stopBtn = document.createElement('button');
       stopBtn.type = 'button';