From cdaec3b7c8146764c13788ed5e073856030c5fdb Mon Sep 17 00:00:00 2001
From: ciregenz <ciregenz@berkeley.edu>
Date: Thu, 11 Jun 2026 03:52:42 -0700
Subject: [PATCH] [eric] chat: prefill caret parks at end (not pos 0) + skip
 the background reconcile-fetch while streaming so a mid-stream reopen stops
 wiping the user bubble

---
 .../src/app/pages/AgentChat/AgentChat.tsx     | 10 +++++++++-
 .../src/app/pages/AgentChat/ChatInput.tsx     | 19 +++++++++++++++++--
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/frontend/src/app/pages/AgentChat/AgentChat.tsx b/frontend/src/app/pages/AgentChat/AgentChat.tsx
index b6592d93..a0441991 100644
--- a/frontend/src/app/pages/AgentChat/AgentChat.tsx
+++ b/frontend/src/app/pages/AgentChat/AgentChat.tsx
@@ -344,7 +344,15 @@ const AgentChat: React.FC<AgentChatProps> = ({ sessionId: sessionIdProp, onClose
       // let the fetch reconcile in the background; awaiting serialized a slow
       // round trip in front of the live stream on every reopen.
       const warm = !!store.getState().agents.sessions[id]?.messages?.length;
-      if (warm) {
+      // Mid-stream reopen: the server snapshot predates the just-sent user turn
+      // (not persisted until the turn ends), and the WS echo already cleared the
+      // bubble's optimistic flag, so the background reconcile would DROP the user
+      // message until the stream finishes. The warm store + the kept-alive socket
+      // are authoritative here, so skip the fetch; stream-end persists everything.
+      const streamingNow = !!store.getState().streaming.bySession[id];
+      if (warm && streamingNow) {
+        // no fetch: don't let a stale snapshot wipe the in-flight turn
+      } else if (warm) {
         dispatch(fetchSession(id));
       } else {
         try {
diff --git a/frontend/src/app/pages/AgentChat/ChatInput.tsx b/frontend/src/app/pages/AgentChat/ChatInput.tsx
index 3b215deb..3f111815 100644
--- a/frontend/src/app/pages/AgentChat/ChatInput.tsx
+++ b/frontend/src/app/pages/AgentChat/ChatInput.tsx
@@ -70,8 +70,23 @@ const ChatInput = forwardRef<ChatInputHandle, Props>(({ onSend, disabled, mode,
     if (!prefillPrompt || prefilledRef.current === prefillPrompt) return;
     const editor = editorRef.current;
     if (!editor) return;
-    if (editor.tagName === 'TEXTAREA') (editor as unknown as HTMLTextAreaElement).value = prefillPrompt;
-    else editor.textContent = prefillPrompt;
+    if (editor.tagName === 'TEXTAREA') {
+      const ta = editor as unknown as HTMLTextAreaElement;
+      ta.value = prefillPrompt;
+      ta.setSelectionRange(prefillPrompt.length, prefillPrompt.length);
+    } else {
+      editor.textContent = prefillPrompt;
+      // Park the caret AFTER the seeded text, not at position 0 (the default for a
+      // freshly-set textContent), so the user types/sends from the end.
+      const sel = window.getSelection();
+      if (sel) {
+        const range = document.createRange();
+        range.selectNodeContents(editor);
+        range.collapse(false);
+        sel.removeAllRanges();
+        sel.addRange(range);
+      }
+    }
     setHasContent(true);
     prefilledRef.current = prefillPrompt;
     editor.style.opacity = '0.5';