Workflows: 5.0.0-beta.5 Zod schema rejects RemoteRef-wrapped step inputs from production service

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Environment
  • SDK: workflow@5.0.0-beta.5 (published 2026-05-11)
  • Worker (server-side, per error User-Agent): @workflow/world-vercel/5.0.0-beta.4
  • Runtime: Node 24, Vercel Functions, fluid compute
  • Framework: Next.js 16.2 (Turbopack, React Compiler)
  • Region: fra1
  • Date observed: 2026-05-13, ~04:00 UTC onward
    Summary
    Every call to start(myWorkflow, […]) returns 500 from our API route. The Workflow service accepts the run (a wrun_* ID is allocated and steps fire), but the SDK throws a
    WorkflowWorldError when validating the response to POST /v3/runs/{runId}/events. The service is now returning step inputs wrapped as { _type: ‘RemoteRef’, _ref: ‘dbrf:…’ }
    (blob-storage refs), but the SDK’s Zod schema requires run.input and step.input as non-optional concrete values.
    Regression history
  • workflow@4.2.4 (until 2026-05-12 evening UTC): worked.
  • Service-side change rolled out overnight 2026-05-12 → 13.
  • workflow@4.2.4 after the change: errored on run.output / run.error / run.completedAt being undefined for in-flight runs.
  • Upgraded to workflow@5.0.0-beta.5: now errors on run.input / step.input.
    Full error (post-upgrade, beta.5)
    Error [WorkflowWorldError]: Schema validation failed for POST /v3/runs/wrun_01KRFVDK2PHG87MGD5XQ9WTKJK/events:
    run.input: Invalid input: expected nonoptional, received undefined
    step.input: Invalid input: expected nonoptional, received undefined
    Response context:
    Content-Type: application/cbor, 2816 bytes (CBOR), preview: {
    event: {
    runId: ‘wrun_XXXX’,
    eventId: ‘evnt_XXXX’,
    correlationId: ‘step_XXXX’,
    eventType: ‘step_created’,
    eventData: {
    stepName: ‘step//./workflows/foo-bar.workflow//fooStep’,
    input: {
    _type: ‘RemoteRef’,
    _ref: ‘dbrf:team_XXXX:prj_XXXXX:production:wrun_XXX:…’
    [cause] ZodError:
    [
    { code: ‘invalid_type’, expected: ‘nonoptional’, path: [‘run’,‘input’], message: ‘Invalid input: expected nonoptional, received undefined’ },
    { code: ‘invalid_type’, expected: ‘nonoptional’, path: [‘step’,‘input’], message: ‘Invalid input: expected nonoptional, received undefined’ }
    ]
    Pre-upgrade (4.2.4) variant of the same class:
    run.output: Invalid input: expected nonoptional, received undefined
    run.error: Invalid input: expected nonoptional, received undefined
    run.completedAt: Invalid input: expected nonoptional, received undefined
    Where it fires
  • Surfaces as Queue callback error on POST /.well-known/workflow/v1/flow for every event the SDK tries to acknowledge.
    Repro
  1. Install workflow@^5.0.0-beta.5 in a Next.js 16 app on Vercel production.
  2. Define a workflow with at least one ‘use step’ function that takes a non-trivial input (anything that the service decides to externalize as a blob ref — we see it on a few-KB
    structured object).
  3. Call start(workflow, [input]) from an API route.
  4. Observe 500 + the error above; verify the run still exists via the Workflow Run viewer.
    What I think the fix is
    Either:
  • (SDK) Loosen the events-response Zod schema: run.input / step.input / run.output / run.error / run.completedAt should all be .optional() or accept the RemoteRef discriminated union - the service legitimately omits them for in-flight runs and externalizes large payloads.
  • (Service) Stop returning bare RemoteRef for input/output in events that hit pre-5.0 SDKs, or inline payloads under some threshold.