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

[adamiBs]

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.

[adamiBs]

Seems related:
#1939

[mglaser12]

Hitting this from a clean Vercel project today (May 14, 2026). Reproduction is fully blocked on both stable and beta. Adding details in case it helps narrow the regression window.

Environment

• Vercel project on a fresh deployment (May 14)
• Build: Nitro 3.0.260429-beta + Vite 5.4.19 (SPA + Express server)
• Runtime: Node 24.x on Vercel Functions, region iad1
• workflow tested at both 4.2.4 (stable) and 5.0.0-beta.5
• zod tested at 4.4.3 (latest in ^4.3.6 range); workflow's own pin is 4.3.6

Trigger
Standard start(myWorkflow, [syncLogId]) from an Express route that's mounted via Nitro. The workflow function has 9 step types and uses Promise.all to fan out monthly per-service syncs. Input is a single integer (the sync_logs primary key) — not a large payload, so it shouldn't be hitting the RemoteRef externalization path, yet the schema validation still fails on run.input and step.input.

v5 beta 5 error

Queue callback error: Error: Schema validation failed for POST /v3/runs/wrun_.../events:
  run.input: Invalid input: expected nonoptional, received undefined
  step.input: Invalid input: expected nonoptional, received undefined

  at createWorkflowRunEvent (file:///var/task/index.mjs:184372:12)
  at trace (file:///var/task/index.mjs:176497:12)

Caused by: ZodError: [
  { "code": "invalid_type", "expected": "nonoptional", "path": ["run","input"], ... },
  { "code": "invalid_type", "expected": "nonoptional", "path": ["step","input"], ... }
]

url: 'https://vercel-workflow.com/api/v3/runs/wrun_.../events'
name: 'WorkflowWorldError'

v4.2.4 stable error (different fields, same shape)

Schema validation failed for POST /v3/runs/wrun_.../events:
  run.output: Invalid input: expected nonoptional, received undefined
  run.error: Invalid input: expected nonoptional, received undefined
  run.completedAt: Invalid input: expected nonoptional, received undefined

Symptoms

• start() returns a runId successfully (run gets created on Vercel's side, visible via npx workflow inspect run <runId>)
• Run sits in status: 'pending' indefinitely
• /.well-known/workflow/v1/flow returns 500 on every queue callback attempt
• Run never executes any steps

Notes

• Even with my input being trivial (single integer), the run.input field is being treated as undefined on the event-creation path. So this isn't only about RemoteRef-wrapped large payloads — the schema mismatch shows up for small concrete inputs too.
• Workflow runtime confirms specVersion: 3 in the run record (npx workflow inspect run <runId>).

Happy to share more reproduction details if useful.