AcpAgent does not support resuming suspended generate calls

Error message

AcpAgent does not support resuming suspended generate calls

What it means

The Mastra server handler for agent version operations requires a configured storage adapter. mastra.getStorage() returns undefined when no storage was configured on the Mastra instance, so the handler aborts with a 500 HTTPException. Agent versioning (list/get/restore) persists to storage and cannot run without it.

Source

Thrown at agent-sdks/acp/src/agent.ts:119

    const text = await this.connection.prompt(
      prompt,
      (options as { abortSignal?: AbortSignal } | undefined)?.abortSignal,
    );
    const messageList = this.createMessageList(messages, text);

    return {
      text,
      response: {
        dbMessages: messageList.get.response.db(),
      },
      toolResults: [],
      finishReason: 'stop',
      runId: options?.runId ?? randomUUID(),
    };
  }

  async resumeGenerate(): Promise<SubAgentGenerateResult> {
    throw new Error('AcpAgent does not support resuming suspended generate calls');
  }

  async resumeStream(): Promise<SubAgentStreamResult> {
    throw new Error('AcpAgent does not support resuming suspended stream calls');
  }

  async stream(messages: MessageListInput, options?: AgentStreamOptions): Promise<SubAgentStreamResult> {
    const runId = options?.runId ?? randomUUID();
    const prompt = this.getPrompt(messages, options?.instructions);
    const signal = (options as { abortSignal?: AbortSignal } | undefined)?.abortSignal;
    const messageList = new MessageList();
    messageList.add(messages, 'input');

    let resolveText!: (text: string) => void;
    let rejectText!: (error: unknown) => void;
    const textPromise = new Promise<string>((resolve, reject) => {
      resolveText = resolve;
      rejectText = reject;

View on GitHub (pinned to 75dd419e61)

Solutions

Configure storage on the Mastra instance, e.g. new Mastra({ storage: new PostgresStore({connectionString: process.env.DATABASE_URL}) })
Verify the configured storage is actually passed to the server/builder that serves the handlers
Confirm getStorage() is not shadowed by an environment-conditional that skips storage in production
Rebuild/redeploy the server so the running instance includes storage

Example fix

// before
export const mastra = new Mastra({ agents: { myAgent } });
// after
export const mastra = new Mastra({
  agents: { myAgent },
  storage: new PostgresStore({ connectionString: process.env.DATABASE_URL }),
});

Defensive patterns

Strategy: try-catch

Validate before calling

const mastra = getMastra();
if (!mastra?.getStorage?.()) {
  throw new Error('Refusing to call agent-version endpoints: no storage configured on Mastra instance');
}

Type guard

function hasStorage(m: unknown): m is { getStorage: () => object } {
  return !!m && typeof (m as any).getStorage === 'function' && !!(m as any).getStorage();
}

Try / catch

try {
  await fetch(`/api/agents/${agentId}/versions/${versionId}`);
} catch (e) {
  if (isHttpError(e) && e.status === 500 && /Storage is not configured/.test(e.message)) {
    // configure storage on the Mastra instance, then retry
  } else throw e;
}

Prevention

Always configure storage in the Mastra constructor, even in dev (use in-memory adapter if needed)
Add a startup assertion that mastra.getStorage() returns a value before serving traffic
Keep storage config out of environment conditionals
Include storage presence in health/readiness checks

When it happens

Trigger: Calling any agent-version HTTP endpoint (e.g. GET/POST /api/agents/:agentId/versions/:versionId) against a Mastra instance constructed without `storage: new MastraStorage(...)` in its options.

Common situations: Local/dev setups where storage was deliberately omitted; configuration stripped when refactoring; using a Mastra builder/server config that forgot the storage key; deploying a server bundle built from an instance that had storage only in dev conditionals.

Related errors

AI-assisted analysis of mastra-ai/mastra@75dd419e61 (2026-08-30). Data as JSON: /api/errors/da3646153b285a28. Report an issue: GitHub.