# 104000: Streamed message could not be finalized

Identifier: `streamed_message_finalize_failed`



Completing or cancelling a streamed message failed. One of its appends was not published, and the follow-up attempt to repair it by re-sending the accumulated content in a single update also failed.

## What you should do

The [step](https://ably.com/docs/ai-transport/concepts/steps.md) producing the message failed, and the partial it had streamed is left on the channel. How you recover depends on how you run the agent:

- **Under a [durable-execution framework](https://ably.com/docs/ai-transport/features/durable-execution.md)** such as Temporal or the Vercel Workflow DevKit, the engine retries the failed step. Keep its `stepId` stable across attempts: the SDK then supersedes the failed attempt rather than appending to it, so the retry replaces the partial on the channel and there is nothing error-specific for you to add.
- **Without a durable-execution framework**, the step will not re-run on its own. Produce the reply again by starting a fresh run, which your application requests rather than the SDK; in a chat client that request is a regenerate.

If re-runs keep failing, inspect the error's `cause` for the underlying publish failure rather than assuming a retry will fix it.

## Why it happens

A streamed message is delivered as an initial publish followed by a series of appends, then finalized with a terminal status of complete or cancelled. Appends are sent fire-and-forget, so a failed append publish is not raised as it happens; it is noticed only when the message is finalized. At that point the SDK tries to repair the message by re-sending its full accumulated content in a single update. This error is raised when that repair publish also fails, so the message is left without a clean terminal state. The originating append failure is preserved as the error's cause.

## What you'll see

The error is reported with code 104000 and status 500. The message names the affected streams, in the form `unable to flush pending appends; recovery failed for stream(s): ...`. In the run pipe it surfaces as the `cause` of a run response stream error (code 104008) rather than at the top level, reaching you through the run's error handling (`RunInfo.error`).