fix: preserve error name through the serialization pipeline for proper error rehydration

[Copilot]

WorkflowNotRegisteredError and StepNotRegisteredError were introduced in #1452 but the serialization pipeline only stored message/stack — dropping the class name. Rehydrated errors were always plain Error instances, making .is() checks silently fail.

Changes

• @workflow/world — Added name?: string to StructuredErrorSchema
• @workflow/core (runtime) — Include name in run_failed event error objects
• @workflow/core (step-handler) — Store StepNotRegisteredError as { message, name } object in step_failed events (was a plain string)
• @workflow/core (step) — Extract name from step_failed error object and set it on the rejected FatalError, so .is() checks work inside workflow catch blocks
• @workflow/errors — WorkflowRunFailedError now sets causeError.name from StructuredError.name, enabling WorkflowNotRegisteredError.is(err.cause)
• @workflow/world-local, @workflow/world-postgres, @workflow/world-vercel — Preserve name when mapping failure events → StructuredError / JSON serialization round-trips

After this change:

try {
  await myStep();
} catch (e) {
  if (StepNotRegisteredError.is(e)) {
    // now reachable — e.name === 'StepNotRegisteredError'
  }
}

// and for run-level errors:
if (WorkflowRunFailedError.is(err)) {
  WorkflowNotRegisteredError.is(err.cause); // true
}

How did you test your changes?

• Updated step-handler.test.ts assertions to match the new structured error object format for StepNotRegisteredError events
• Added a unit test in step.test.ts verifying that error.name is preserved from step_failed event data
• All 494 unit tests pass across @workflow/core, @workflow/world-local, and @workflow/world-vercel

PR Checklist - Required to merge

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• 📝 Ping @vercel/workflow in a comment once the PR is ready, and the above checklist is complete

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[changeset-bot]

🦋 Changeset detected

Latest commit: a784114

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 21 packages

Name	Type
@workflow/core	Patch
@workflow/errors	Patch
@workflow/world	Patch
@workflow/world-local	Patch
@workflow/world-vercel	Patch
@workflow/world-postgres	Patch
@workflow/builders	Patch
@workflow/cli	Patch
@workflow/next	Patch
@workflow/nitro	Patch
@workflow/vitest	Patch
@workflow/web-shared	Patch
workflow	Patch
@workflow/world-testing	Patch
@workflow/astro	Patch
@workflow/nest	Patch
@workflow/rollup	Patch
@workflow/sveltekit	Patch
@workflow/vite	Patch
@workflow/nuxt	Patch
@workflow/ai	Patch

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