deepseek-ai/deepseek-harness · error · SessionForkError

OPEN_TURN

OPEN_TURN

Error message

fork boundary ${boundary} in session "${session.id}" ends inside open turn ${lastTurnBoundary.data.turn}

What it means

Error "fork boundary ${boundary} in session "${session.id}" ends inside open turn ${lastTurnBoundary.data.turn}" thrown in deepseek-ai/deepseek-harness.

Source

Thrown at packages/core/session/src/index.ts:1131

    if (boundary >= events.length) {
      const lastSeq = events.at(-1)?.seq
      throw new SessionForkError(
        `fork boundary ${boundary} does not exist in session "${session.id}" (last seq: ${lastSeq ?? 'none'})`,
        'INVALID_BOUNDARY',
      )
    }

    const boundaryEvent = events[boundary]
    if (boundaryEvent === undefined || boundaryEvent.seq !== boundary) {
      throw new SessionForkError(
        `fork boundary ${boundary} does not match a contiguous event seq in session "${session.id}"`,
        'INVALID_BOUNDARY',
      )
    }
    const lastTurnBoundary = events.slice(0, boundary + 1)
      .findLast(event => event.type === 'turn/start' || event.type === 'turn/end')
    if (lastTurnBoundary?.type === 'turn/start') {
      throw new SessionForkError(
        `fork boundary ${boundary} in session "${session.id}" ends inside open turn ${lastTurnBoundary.data.turn}`,
        'OPEN_TURN',
      )
    }

    return events.slice(0, boundary + 1)
  }

  private _resolveForkSource(source: SessionForkSource): Session {
    if (typeof source === 'string') {
      const session = this.get(source)
      if (session === undefined) throw new SessionForkError(`session "${source}" not found`, 'SESSION_NOT_FOUND')
      return session
    }

    const live = this.get(source.id)
    if (live === undefined) {
      throw new SessionForkError(`session "${source.id}" not found`, 'SESSION_NOT_FOUND')

View on GitHub (pinned to b150a551b8)

When it happens

Trigger: Thrown at packages/core/session/src/index.ts:1131 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/3d1aacb7ff6aacba. Report an issue: GitHub.