fix(ui): restrict edit to latest user message (#747)

fix(ui): restrict edit to latest user message (#747)

Only the latest user turn shows the pencil/edit affordance. Older user
messages remain read-only (copy + timestamp still work). Avoids the
misleading implication that historical messages can be lightly edited
when the actual action truncates the session and restarts the
conversation from that point.

Closes #744

Co-authored-by: franksong2702 <franksong2702@users.noreply.github.com>

tests/test_issue744.py

@@ -0,0 +1,9 @@
+import pathlib
+
+
+def test_only_latest_user_message_gets_edit_button():
+    src = pathlib.Path("static/ui.js").read_text(encoding="utf-8")
+    assert "let lastUserRawIdx=-1;" in src
+    assert "const isEditableUser=isUser&&rawIdx===lastUserRawIdx;" in src
+    assert "const editBtn  = isEditableUser ?" in src
+