deepseek-ai/deepseek-harness · error · SessionForkError

SESSION_ALREADY_EXISTS

SESSION_ALREADY_EXISTS

Error message

session "${childSessionId}" already exists

What it means

Error "session "${childSessionId}" already exists" thrown in deepseek-ai/deepseek-harness.

Source

Thrown at packages/core/session/src/index.ts:1083

  }

  /**
   * Create a live child session from a stable prefix of a live source.
   * `boundary` is an inclusive source event seq; omitted means the source's
   * current last event. The selected slice may end with a between-turn event
   * but must not end inside an open turn.
   *
   * @param source - Live source session object or id.
   * @param boundary - Inclusive source event seq to fork through; omitted means
   *   the source's current last event, and omitted on an empty source forks an
   *   empty child.
   * @param childSessionId - Optional child session id; omitted delegates to
   *   `SessionStore`'s id policy.
   * @returns The created live child session.
   */
  fork(source: SessionForkSource, boundary?: number, childSessionId?: SessionId): Session {
    if (childSessionId !== undefined && this.get(childSessionId) !== undefined) {
      throw new SessionForkError(`session "${childSessionId}" already exists`, 'SESSION_ALREADY_EXISTS')
    }
    const liveSource = this._resolveForkSource(source)
    const seed = this._forkSeed(liveSource, boundary)
    return this.create(childSessionId, {
      seed,
      meta: {
        ...liveSource.header.cwd !== undefined ? { cwd: liveSource.header.cwd } : {},
        parentSession: liveSource.id,
        seedLength: seed.length,
      },
    })
  }

  private _forkSeed(session: Session, requestedBoundary: number | undefined): SessionEvent[] {
    const events = session.events
    const lastEvent = events.at(-1)
    let boundary: number
    if (requestedBoundary !== undefined) {

View on GitHub (pinned to b150a551b8)

When it happens

Trigger: Thrown at packages/core/session/src/index.ts:1083 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/b441e127868b8ea7. Report an issue: GitHub.