fix: guard against non-string content delta and thinking blocks

tianhaocui · tianhaocui · commit d76a97e2956b · 2026-04-19T15:14:50.000+08:00
Mistral (and potentially other providers) may send thinking content as an object in choice.delta.content rather than a string. Without a type guard, the object is coerced to "[object Object]" when appended to the text buffer. Two fixes: 1. openai-transport-stream.ts: add typeof === "string" check on choice.delta.content before appending to the text buffer 2. message-extract.ts: handle object-form thinking blocks where the text lives in a .text property instead of being a plain string Fixes #68309
diff --git a/src/agents/openai-transport-stream.ts b/src/agents/openai-transport-stream.ts
@@ -1182,7 +1182,7 @@ async function processOpenAICompletionsStream(
     if (!choice.delta) {
       continue;
     }
-    if (choice.delta.content) {
+    if (typeof choice.delta.content === "string" && choice.delta.content) {
       if (currentBlock?.type === "toolCall") {
         queuePostToolCallDelta({ kind: "text", text: choice.delta.content });
       } else {
diff --git a/ui/src/ui/chat/message-extract.ts b/ui/src/ui/chat/message-extract.ts
@@ -48,10 +48,20 @@ export function extractThinking(message: unknown): string | null {
   if (Array.isArray(content)) {
     for (const p of content) {
       const item = p as Record<string, unknown>;
-      if (item.type === "thinking" && typeof item.thinking === "string") {
-        const cleaned = item.thinking.trim();
-        if (cleaned) {
-          parts.push(cleaned);
+      if (item.type === "thinking") {
+        const thinkingValue =
+          typeof item.thinking === "string"
+            ? item.thinking
+            : typeof item.thinking === "object" &&
+                item.thinking !== null &&
+                typeof (item.thinking as Record<string, unknown>).text === "string"
+              ? ((item.thinking as Record<string, unknown>).text as string)
+              : null;
+        if (thinkingValue) {
+          const cleaned = thinkingValue.trim();
+          if (cleaned) {
+            parts.push(cleaned);
+          }
         }
       }
     }

Original file line number	Diff line number	Diff line change
`@@ -1182,7 +1182,7 @@ async function processOpenAICompletionsStream(`
`1182`	`1182`	`if (!choice.delta) {`
`1183`	`1183`	`continue;`
`1184`	`1184`	`}`
`1185`		`- if (choice.delta.content) {`
	`1185`	`+ if (typeof choice.delta.content === "string" && choice.delta.content) {`
`1186`	`1186`	`if (currentBlock?.type === "toolCall") {`
`1187`	`1187`	`queuePostToolCallDelta({ kind: "text", text: choice.delta.content });`
`1188`	`1188`	`} else {`