deepseek-ai/deepseek-harness · error

agent-preset-locked

agent-preset-locked

Error message

session "${sessionId}" has already started; its agent preset is fixed

What it means

Error "session "${sessionId}" has already started; its agent preset is fixed" thrown in deepseek-ai/deepseek-harness.

Source

Thrown at packages/host/apiproxy/src/api-proxy.ts:3004

      // agent and the session survive, only the composition is swapped.
      async select(request) {
        const { sessionId, agentPreset } = request.payload
        const presets = ctx.get('agentPresets')
        if (presets === undefined) {
          return err(request, {
            code: 'agent-preset-not-found',
            message: 'this deployment composes no agent presets',
            details: { agentPreset, available: [] },
          })
        }
        const found = await agentFor(sessionId)
        if ('error' in found) return err(request, found.error)
        const { agent } = found
        const swap = async (): Promise<RpcResponse<{ agentPreset: string }>> => {
          // Re-read inside the queue: an earlier switch may have run, and a
          // conversation may have started, since this request arrived.
          if (!sessionBlank(agent.session)) {
            return err(request, {
              code: 'agent-preset-locked',
              message: `session "${sessionId}" has already started; its agent preset is fixed`,
              details: { sessionId, agentPreset },
            })
          }
          try {
            const preset = await presets.recompose(agent.ctx, agentPreset)
            // Recorded only after the swap committed: the log states what the
            // agent runs, and a rejected mount leaves the previous composition.
            agent.session.append('agent-preset/selected', { agentPreset: preset.id })
            return ok(request, { agentPreset: preset.id })
          } catch (error: unknown) {
            const refused = presetFailure(request, error)
            if (refused !== undefined) return refused
            return err(request, {
              code: 'internal',
              message: `failed to select agent preset "${agentPreset}": ${String(error)}`,
              details: {},

View on GitHub (pinned to b150a551b8)

Solutions

1. The agent preset is fixed once a session has started; create a new session with the desired preset.

When it happens

Trigger: Thrown at packages/host/apiproxy/src/api-proxy.ts:3004 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/edf5007968798a5b. Report an issue: GitHub.