fix(core,a2a): group cancelled tool responses and coalesce consecutive roles to prevent 400 Bad Request (#28407)

packages/a2a-server/src/agent/task.ts

@@ -1092,19 +1092,21 @@ export class Task {
     logger.info(
       `[Task] Adding ${completedTools.length} tool responses to history without generating a new response.`,
     );
-    const responsesToAdd = completedTools.flatMap(
-      (toolCall) => toolCall.response.responseParts,
-    );
-
-    for (const response of responsesToAdd) {
-      let parts: genAiPart[];
-      if (Array.isArray(response)) {
-        parts = response;
-      } else if (typeof response === 'string') {
-        parts = [{ text: response }];
-      } else {
-        parts = [response];
+    const parts: genAiPart[] = [];
+    for (const toolCall of completedTools) {
+      const response = toolCall.response?.responseParts;
+      if (!response) {
+        continue;
       }
+      if (Array.isArray(response)) {
+        parts.push(...response);
+      } else if (typeof response === 'string') {
+        parts.push({ text: response });
+      } else {
+        parts.push(response);
+      }
+    }
+    if (parts.length > 0) {
       // eslint-disable-next-line @typescript-eslint/no-floating-promises
       this.geminiClient.addHistory({
         role: 'user',