deepseek-ai/deepseek-harness · error · Error

seed event at index ${index} uses unsupported legacy request

Error message

seed event at index ${index} uses unsupported legacy request/header-delta format

What it means

Error "seed event at index ${index} uses unsupported legacy request/header-delta format" thrown in deepseek-ai/deepseek-harness.

Source

Thrown at packages/core/session/src/index.ts:216

  const pending: object[] = [value]
  while (pending.length > 0) {
    // The non-empty check proves an object remains to visit.
    // oxlint-disable-next-line typescript/no-non-null-assertion
    const current = pending.pop()!
    Object.freeze(current)
    for (const key in current) {
      const child = (current as Record<string, unknown>)[key]
      if (child !== null && typeof child === 'object') pending.push(child)
    }
  }
  return value
}

/** Validate the fixed event envelope after one-pass JSON materialization. */
function assertSessionEventEnvelope(value: Record<string, unknown>, index: number): asserts value is SessionEvent {
  const event = value
  if (event['type'] === 'request/header-delta') {
    throw new Error(`seed event at index ${index} uses unsupported legacy request/header-delta format`)
  }
  for (const key in event) {
    switch (key) {
      case 'type':
      case 'seq':
      case 'time':
      case 'data':
      case 'surfaceOp':
      case 'sourceEventSeqs':
      case 'ignorable':
        break
      default:
        throw new Error(`seed event at index ${index} has an invalid event envelope`)
    }
  }
  const type = event['type']
  const seq = event['seq']
  const time = event['time']

View on GitHub (pinned to b150a551b8)

Solutions

1. Migrate the legacy request/header-delta format before seeding the session.

When it happens

Trigger: Thrown at packages/core/session/src/index.ts:216 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of deepseek-ai/deepseek-harness@b150a551b8 (2026-08-24). Data as JSON: /api/errors/b2866e3f570a8870. Report an issue: GitHub.