Issue with Zod 4.4.x -> Invalid input: expected nonoptional, received undefined

[ziyak97]

Sharing what i believe could be the cause of this issue -

const EventResultResolveWireSchema = z.object({
  event: EventSchema.optional(),
  run: WorkflowRunSchema.optional(),
  step: StepWireSchema.optional(),
  hook: HookSchema.optional(),
  events: z.array(EventSchema).optional(),
});
For some events, including run_started, Workflow validates the response from Vercel using WorkflowRunSchema. That schema is here:

export const WorkflowRunSchema = z.discriminatedUnion('status', [
  WorkflowRunBaseSchema.extend({
    status: z.enum(['pending', 'running']),
    output: z.undefined(),
    error: z.undefined(),
    completedAt: z.undefined(),
  }),
  ...
]);
That means: when a run is pending or running, Workflow expects output, error, and completedAt to be undefined.

But with your top-level zod@4.4.2, Zod is treating these missing fields as required/nonoptional, so when Vercel returns a running run like:

{
  status: "running",
  // no output
  // no error
  // no completedAt
}
Zod throws:

run.output: expected nonoptional, received undefined
run.error: expected nonoptional, received undefined
run.completedAt: expected nonoptional, received undefined

I have added this comment on a Zod issue as well -> colinhacks/zod#5917 (comment)

Using workflow 5.0.0-beta-4

[softmarshmallow]

+1, hit the exact same error on workflow@5.0.0-beta.4 end-to-end (also reproduces on 4.2.4 and 4.2.3). Workflows die at attempt 1 of the very first message because world-local's storage validates run records with WorkflowRunSchema, but JSON.stringify strips undefined keys from the on-disk run JSON, so on read-back the missing output/error/completedAt fields fail Zod 4.3+'s strict z.undefined() check.

Suggested upstream fix

In @workflow/world/src/runs.ts WorkflowRunSchema, change every z.undefined() to z.undefined().optional(). With .optional() the field accepts both missing key and key present with undefined value, which matches both legacy and current Zod semantics. Equivalent for downstream consumers.

A patch on dist/runs.js:

 export const WorkflowRunSchema = z.discriminatedUnion('status', [
     WorkflowRunBaseSchema.extend({
         status: z.enum(['pending', 'running']),
-        output: z.undefined(),
-        error: z.undefined(),
-        completedAt: z.undefined(),
+        output: z.undefined().optional(),
+        error: z.undefined().optional(),
+        completedAt: z.undefined().optional(),
     }),
     WorkflowRunBaseSchema.extend({
         status: z.literal('cancelled'),
-        output: z.undefined(),
-        error: z.undefined(),
+        output: z.undefined().optional(),
+        error: z.undefined().optional(),
         completedAt: z.coerce.date(),
     }),
     WorkflowRunBaseSchema.extend({
         status: z.literal('completed'),
         output: SerializedDataSchema,
-        error: z.undefined(),
+        error: z.undefined().optional(),
         completedAt: z.coerce.date(),
     }),
     WorkflowRunBaseSchema.extend({
         status: z.literal('failed'),
-        output: z.undefined(),
+        output: z.undefined().optional(),
         error: StructuredErrorSchema,
         completedAt: z.coerce.date(),
     }),
 ]);

Local workaround (for anyone blocked)

We use bun patch to apply the diff above against @workflow/world. It auto-applies on every install and persists across CI:

// package.json
{
  "patchedDependencies": {
    "@workflow/world@5.0.0-beta.1": "patches/@workflow%2fworld@5.0.0-beta.1.patch"
  }
}

Verified end-to-end: previously every workflow run failed at attempt 1 with the schema error; with the patch applied, our 5-stage pipeline (concept → world_spec → wave A fanout → wave B → post-process) completes cleanly through world-local.

Note: @workflow/world-local@5.0.0-beta.10 (newer than what workflow@5.0.0-beta.4 pulls in transitively) ships with zod@4.1.11 pinned, which is the pre-strict Zod that papers over the issue at the resolver level. But that newer world-local has API renames incompatible with core@5.0.0-beta.4 (createLocalWorld not exported), so a simple overrides bump doesn't work. The schema fix above is the right fundamental change.