fix(ui): use content-level comparison for tail duplicate detection

SebTardif · SebTardif · commit 6a452a818a1b · 2026-06-03T21:51:52.000-07:00
The previous isTailDuplicate used messageDisplaySignature which only
compared text content, causing false positives when two messages had
the same text but different content structure (e.g., text-only vs
text+canvas). Switch to JSON.stringify comparison of content arrays
so messages with different block types or counts are not incorrectly
deduplicated.

This fixes the upstream test 'keeps repeated assistant final text
within the same turn' which expects both a text-only and a
text+canvas message to be preserved even when they share the same
display text.

Signed-off-by: Sebastien Tardif &lt;sebtardif@ncf.ca&gt;
diff --git a/ui/src/ui/controllers/chat.ts b/ui/src/ui/controllers/chat.ts
@@ -1228,12 +1228,17 @@ function isTailDuplicate(messages: unknown[], candidate: unknown): boolean {
   if (messages.length === 0) {
     return false;
   }
-  const candidateSig = messageDisplaySignature(candidate);
-  if (!candidateSig) {
+  const tail = messages[messages.length - 1];
+  if (!tail || !candidate || typeof tail !== "object" || typeof candidate !== "object") {
+    return false;
+  }
+  const tailContent = (tail as { content?: unknown }).content;
+  const candidateContent = (candidate as { content?: unknown }).content;
+  try {
+    return JSON.stringify(tailContent) === JSON.stringify(candidateContent);
+  } catch {
     return false;
   }
-  const tailSig = messageDisplaySignature(messages[messages.length - 1]);
-  return tailSig === candidateSig;
 }
 
 export function handleChatEvent(state: ChatState, payload?: ChatEventPayload) {
