deepseek-ai/deepseek-harness · error · TypeError

child result is not losslessly JSON-serializable

Error message

child result is not losslessly JSON-serializable

What it means

Error "child result is not losslessly JSON-serializable" thrown in deepseek-ai/deepseek-harness.

Source

Thrown at packages/workflow/workflow-worker-thread/src/host.ts:398

        this.ctx.logger.warn(`workflow-worker-thread: refused child dispose failed: ${renderThrown(error)}`)
      }
      return
    }

    const record: ChildRecord = { run }
    this.children.set(callId, record)
    // Attach result forwarding before publishing the child handle. Because the
    // callback itself runs in a later microtask, ChildStarted is still posted
    // first even for an already-settled scripted provider.
    const forwardResult = run.result.then<() => void, () => void>(
      (result) => {
        try {
          const snapshot = snapshotJsonValue<ChildResult>({
            output: result.output,
            ...result.structured !== undefined ? { structured: result.structured } : {},
            stopReason: result.stopReason,
          })
          if (snapshot === undefined) throw new TypeError('child result is not losslessly JSON-serializable')
          return () => { this.post(HostToWorkerType.ChildSettled, { callId, result: snapshot }) }
        } catch (error: unknown) {
          const rendered = `workflow child result could not cross the worker boundary: ${renderThrown(error)}`
          return () => { this.post(HostToWorkerType.ChildFailed, { callId, rendered }) }
        }
      },
      (error: unknown) => {
        const rendered = renderThrown(error)
        return () => { this.post(HostToWorkerType.ChildFailed, { callId, rendered }) }
      },
    )
    this.post(HostToWorkerType.ChildStarted, { callId, childId: run.id })
    void forwardResult.then((forward) => { forward() })
  }

  private onChildDispose(callId: number): void {
    const record = this.children.get(callId)
    if (record === undefined) {

View on GitHub (pinned to b150a551b8)

Solutions

1. Have the child workflow return only losslessly JSON-serializable data (plain objects, arrays, strings, finite numbers, booleans, null).

When it happens

Trigger: Thrown at packages/workflow/workflow-worker-thread/src/host.ts:398 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/d329408cf319beac. Report an issue: GitHub.