deepseek-ai/deepseek-harness · error · Error

session "${sessionId}" already exists

Error message

session "${sessionId}" already exists

What it means

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

Source

Thrown at packages/core/session/src/index.ts:871

   * @param options - seed events and/or creation metadata for the header. With
   *   `seedSource: 'persistence'`, metadata and events must be fresh detached
   *   graphs whose ownership transfers to this call: they are validated and
   *   frozen in place through {@link Session.fromRestore}, so the caller must
   *   retain no mutable aliases.
   * @returns the constructed session, NOT yet in the store.
   * @throws if a session with `id` already exists, metadata is not a plain
   *   lossless-JSON record with valid scalar fields, or `meta.cwd` is a
   *   non-absolute path.
   */
  prepare(id?: SessionId, options?: PrepareSessionOptions): Session {
    let sessionId: SessionId
    if (id === undefined) {
      do sessionId = SessionId(`session-${++this.counter}`)
      while (this.store.has(sessionId))
    } else {
      sessionId = SessionId(id)
    }
    if (this.store.has(sessionId)) throw new Error(`session "${sessionId}" already exists`)
    if (options?.seedSource === 'persistence') {
      return Session.fromRestore(sessionId, options.seed, options.meta)
    }
    const seed = options?.seed
    const meta = options?.meta
    const header: SessionHeader = {
      version: SESSION_FORMAT_VERSION,
      id: sessionId,
      createdAt: meta?.createdAt ?? Date.now(),
      ...meta?.cwd === undefined ? {} : { cwd: meta.cwd },
      ...meta?.parentSession === undefined ? {} : { parentSession: meta.parentSession },
      ...meta?.seedLength === undefined ? {} : { seedLength: meta.seedLength },
      ...meta?.origin === undefined ? {} : { origin: meta.origin },
      ...meta?.delegationDepth === undefined ? {} : { delegationDepth: meta.delegationDepth },
      ...meta?.agentPreset === undefined ? {} : { agentPreset: meta.agentPreset },
    }
    return Session.create(sessionId, seed, header)
  }

View on GitHub (pinned to b150a551b8)

When it happens

Trigger: Thrown at packages/core/session/src/index.ts:871 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/4e2460ac0e875917. Report an issue: GitHub.