Fix: restore event round trip in VertexAiSessionService

core/src/sessions/vertex_ai_session_service.ts

@@ -7,6 +7,7 @@
 import {Client} from '@google-cloud/vertexai/build/src/genai/client.js';
 import {Sessions} from '@google-cloud/vertexai/build/src/genai/sessions.js';
 import {
+  EventActions as ApiEventActions,
   AppendAgentEngineSessionEventConfig,
   AppendAgentEngineSessionEventRequestParameters,
   EventMetadata,
@@ -40,6 +41,7 @@ import {createSession, Session} from './session.js';
 const DEFAULT_MAX_ATTEMPTS = 30;
 const GRPC_NOT_FOUND = 5;
 const HTTP_NOT_FOUND = 404;
+const HTTP_BAD_REQUEST = 400;
 
 /**
  * Checks if the given URI is a Vertex AI session service URI.
@@ -431,12 +433,16 @@ export class VertexAiSessionService extends BaseSessionService {
     }
 
     const config = partialCopy<AppendAgentEngineSessionEventConfig>(event, [
-      'content',
-      'actions',
       'errorCode',
       'errorMessage',
     ]);
 
+    const content = event.content && dropUnsupportedPartFields(event.content);
+    config.content = content;
+    config.actions = event.actions
+      ? toApiEventActions(event.actions)
+      : undefined;
+
     config.eventMetadata = {
       ...partialCopy<EventMetadata>(event, [
         'partial',
@@ -450,7 +456,7 @@ export class VertexAiSessionService extends BaseSessionService {
         Object.keys(customMetadata).length > 0 ? customMetadata : undefined,
     };
 
-    config.rawEvent = JSON.parse(JSON.stringify(event)) as Record<
+    config.rawEvent = JSON.parse(JSON.stringify({...event, content})) as Record<
       string,
       unknown
     >;
@@ -466,24 +472,66 @@ export class VertexAiSessionService extends BaseSessionService {
     try {
       await this.sessions.events.append(params);
     } catch (error) {
+      if (!isInvalidArgumentError(error)) {
+        throw error;
+      }
       logger.warn(
-        'Failed to append event with rawEvent, falling back...',
+        'appendEvent was rejected with rawEvent; retrying without it.',
         error,
       );
       delete config.rawEvent;
-      await this.sessions.events.append({
-        name: `reasoningEngines/${reasoningEngineId}/sessions/${session.id}`,
-        author: event.author || 'user',
-        invocationId: event.invocationId || `inv-${Date.now()}`,
-        timestamp: new Date(event.timestamp).toISOString(),
-        config,
-      });
+      await this.sessions.events.append(params);
     }
 
     return event;
   }
 }
 
+/**
+ * Returns a copy of `content` without Part fields the Agent Engine Sessions
+ * API rejects.
+ *
+ * `partMetadata` is a Gemini Developer API-only field; the Sessions API fails
+ * appendEvent with 400 INVALID_ARGUMENT ("Unknown name \"part_metadata\"").
+ */
+function dropUnsupportedPartFields(content: Content): Content {
+  if (!content.parts) {
+    return content;
+  }
+  return {
+    ...content,
+    parts: content.parts.map((part) => {
+      const copy = {...part};
+      delete copy.partMetadata;
+      return copy;
+    }),
+  };
+}
+
+/**
+ * Maps ADK `EventActions` onto the Sessions API wire shape. ADK's
+ * `transferToAgent` is the API's `transferAgent` (adk-python writes the same
+ * field as `transfer_agent`); every other field keeps its name, including
+ * `requestedToolConfirmations`, which the SDK type omits but `_fromApiEvent`
+ * reads back.
+ */
+function toApiEventActions(actions: EventActions): ApiEventActions {
+  const {transferToAgent, ...rest} = actions;
+  return {...rest, transferAgent: transferToAgent};
+}
+
+/**
+ * True when the service rejected the request payload itself, which is what an
+ * API that does not know `rawEvent` returns. Any other failure must propagate:
+ * the event may already be persisted, so retrying would append it twice.
+ *
+ * Matched structurally on the `ApiError`'s `status`, for the reason given in
+ * getSession's catch.
+ */
+function isInvalidArgumentError(error: unknown): boolean {
+  return (error as {status?: number} | null)?.status === HTTP_BAD_REQUEST;
+}
+
 interface ExtendedEventActions extends EventActions {
   compaction?: {
     startTime: number;
@@ -554,7 +602,12 @@ function _fromApiEvent(apiEventObj: VertexAiSessionEvent): Event {
         'requestedToolConfirmations'
       ] as Record<string, ToolConfirmation>) || {},
     skipSummarization: actions['skipSummarization'] as boolean | undefined,
-    transferToAgent: actions['transferAgent'] as string | undefined,
+    // Earlier adk-js versions copied `event.actions` onto the request
+    // verbatim, so sessions they wrote store ADK's own `transferToAgent` key.
+    transferToAgent: (actions['transferAgent'] ??
+      (actions as Record<string, unknown>)['transferToAgent']) as
+      | string
+      | undefined,
     escalate: actions['escalate'] as boolean | undefined,
     compaction: compactionData || undefined,
   };
@@ -574,6 +627,7 @@ function _fromApiEvent(apiEventObj: VertexAiSessionEvent): Event {
     turnComplete: eventMetadata['turnComplete'] as boolean | undefined,
     interrupted: eventMetadata['interrupted'] as boolean | undefined,
     branch: eventMetadata['branch'] as string | undefined,
+    groundingMetadata: eventMetadata.groundingMetadata,
     customMetadata,
     longRunningToolIds: eventMetadata['longRunningToolIds'] as
       | string[]