fix: subagent tool result parsing

packages/core/src/subagents/subagent-events.ts

@@ -74,6 +74,7 @@ export interface SubAgentToolResultEvent {
   success: boolean;
   error?: string;
   responseParts?: Part[];
+  resultDisplay?: string;
   durationMs?: number;
   timestamp: number;
 }

packages/core/src/subagents/subagent.ts

@@ -620,6 +620,17 @@ export class SubAgentScope {
             success,
             error: errorMessage,
             responseParts: call.response.responseParts,
+            /**
+             * Tools like todoWrite will add some extra contents to the result,
+             * making it unable to deserialize the `responseParts` to a JSON object.
+             * While `resultDisplay` is normally a string, if not we stringify it,
+             * so that we can deserialize it to a JSON object when needed.
+             */
+            resultDisplay: call.response.resultDisplay
+              ? typeof call.response.resultDisplay === 'string'
+                ? call.response.resultDisplay
+                : JSON.stringify(call.response.resultDisplay)
+              : undefined,
             durationMs: duration,
             timestamp: Date.now(),
           } as SubAgentToolResultEvent);