workflow/docs/api-reference/workflow-errors/in-band-superseded-error.mdx

Workflow SDK - Build durable, resilient, and observable workflows

---
title: InBandSupersededError
description: A World throws this error when it refuses an in-band write from an orchestrator invocation that another invocation of the same run has superseded.
type: reference
summary: InBandSupersededError is the in-band fence's refusal. The runtime handles it by stopping the superseded orchestrator invocation, which sends the queue messages its own writes owe and then asks for a redelivery of its message.
related:
  - /docs/api-reference/workflow-errors/workflow-world-error
  - /docs/changelog/spec-9
---

A World throws `InBandSupersededError` (HTTP 412, code `in-band-superseded`) when it refuses a write made by a run's orchestrator because another invocation of the same run's orchestrator has written in-band since this one loaded the event log. It applies only to runs of the experimental spec 9 runtime (`WORKFLOW_SPEC_VERSION=9`).

<Callout>
The Workflow runtime handles this error. The refused invocation stops writing, sends the queue messages its own committed writes still owe, and asks for a redelivery of its queue message instead of acknowledging it. You will only encounter it when interacting with World storage APIs directly.
</Callout>

See [The in-band fence](/docs/changelog/spec-9#the-in-band-fence) on the spec 9 page.

```typescript lineNumbers
import { InBandSupersededError } from "workflow/errors"
declare const world: { events: { create(...args: any[]): Promise<any> } }; // @setup
declare const runId: string; // @setup
declare const event: any; // @setup

try {
  await world.events.create(runId, event, { inBand: true, expectedSeqInBand: 3 });
} catch (error) {
  if (InBandSupersededError.is(error)) { // [!code highlight]
    console.log("Another orchestrator invocation holds this run");
  }
}
```

## API signature

### Properties

<TSDoc
definition={`
interface InBandSupersededError {
  /** The run's highest allocated position at the refusal, when the World reports it. Diagnostic only. */
  seq?: number;
  /** The run's in-band position count at the refusal, when the World reports it. Diagnostic only: never adopt it. */
  seqInBand?: number;
  /** HTTP status: 412. */
  status?: number;
  /** Error code: 'in-band-superseded'. */
  code?: string;
  /** The error message. */
  message: string;
}
export default InBandSupersededError;`}
/>

### Static methods

#### `InBandSupersededError.is(value)`

Type-safe check for `InBandSupersededError` instances. Preferred over `instanceof` because it works across module boundaries and VM contexts.

```typescript
import { InBandSupersededError } from "workflow/errors"
declare const error: unknown; // @setup

if (InBandSupersededError.is(error)) {
  // error is typed as InBandSupersededError
}
```