deepseek-ai/deepseek-harness · error · Error

session append cannot reenter while another append is being

Error message

session append cannot reenter while another append is being published

What it means

Error "session append cannot reenter while another append is being published" thrown in deepseek-ai/deepseek-harness.

Source

Thrown at packages/core/session/src/index.ts:625

    ...opts: T extends SurfaceEventType ? [opts: SurfaceIntent] : []
  ): SessionEvent<T> {
    const surfaceOpts: SurfaceIntent | undefined = opts[0]
    const surfaceMetadata = {
      ...surfaceOpts?.sourceEventSeqs === undefined ? {} : { sourceEventSeqs: surfaceOpts.sourceEventSeqs },
      ...surfaceOpts?.surfaceOp === undefined ? {} : { surfaceOp: surfaceOpts.surfaceOp },
    }
    const dataSnapshot = snapshotJsonValue(data)
    if (dataSnapshot === undefined) {
      throw new Error(`session event "${type}" carries non-JSON-serializable data`)
    }
    assertSupportedRequestHeader(type, dataSnapshot, `session event "${type}"`)
    const surfaceMetadataSnapshot = snapshotJsonValue(surfaceMetadata)
    if (surfaceMetadataSnapshot === undefined) {
      throw new Error(`session event "${type}" carries non-JSON-serializable surface metadata`)
    }
    const entry = attachments.get(this)
    if (entry?.appending) {
      throw new Error('session append cannot reenter while another append is being published')
    }
    const event = deepFreeze({
      type,
      seq: this.log.length,
      time: Date.now(),
      data: dataSnapshot,
      ...(surfaceMetadataSnapshot as { surfaceOp?: unknown; sourceEventSeqs?: unknown }),
    } as unknown as SessionEvent<T>)
    this.surfaceManager.validateNext(event as SessionEvent)

    if (entry !== undefined) entry.appending = true
    try {
      let callbacks: SessionCallback[] | undefined
      const callbackArgs: unknown[] = [this, event]
      if (entry !== undefined) {
        callbacks = collectSessionCallbacks(entry.emitCtx, [entry.carrier, 'session/event', ...callbackArgs])
      }
      this.log.push(event as SessionEvent)

View on GitHub (pinned to b150a551b8)

When it happens

Trigger: Thrown at packages/core/session/src/index.ts:625 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/a1bd0b5049b50d58. Report an issue: GitHub.