From b396b71c6f58671661d458ab66599065130d8d5d Mon Sep 17 00:00:00 2001
From: Kit Langton <kit.langton@gmail.com>
Date: Mon, 18 May 2026 16:04:07 -0400
Subject: [PATCH] fix(ui): guard reasoning renderer against undefined text
 (#28222)

---
 packages/ui/src/components/message-part.tsx | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/ui/src/components/message-part.tsx b/packages/ui/src/components/message-part.tsx
index acf0c9dee3..eeaf895e29 100644
--- a/packages/ui/src/components/message-part.tsx
+++ b/packages/ui/src/components/message-part.tsx
@@ -1563,7 +1563,7 @@ PART_MAPPING["reasoning"] = function ReasoningPartDisplay(props) {
   const streaming = createMemo(
     () => props.message.role === "assistant" && typeof (props.message as AssistantMessage).time.completed !== "number",
   )
-  const text = () => (data.store.part_text_accum_delta?.[part().id] ?? part().text).trim()
+  const text = () => (data.store.part_text_accum_delta?.[part().id] ?? part().text ?? "").trim()
 
   return (
     <Show when={text()}>