Add first-class serialization for FatalError and RetryableError by TooTallNate · Pull Request #1513 · vercel/workflow

TooTallNate · 2026-03-24T21:56:59Z

Summary

Add WORKFLOW_SERIALIZE / WORKFLOW_DESERIALIZE static methods to FatalError and RetryableError in @workflow/errors
Add @workflow/serde as a dependency of @workflow/errors
This enables the SWC plugin to discover and register these classes through the standard class serialization pipeline — no manual registration or explicit serialization entries needed
Add unit tests verifying Instance-based round-trip serialization
Add e2e workflow tests verifying class identity preservation end-to-end (instanceof FatalError, instanceof RetryableError)

Context

This is PR 3 of 5 in a series to improve error handling in Workflow DevKit. Stacked on top of #1512.

Add first-class serialization for built-in Error subclasses #1511 — First-class serde for built-in Error subclasses
Add DOMException to VM context and first-class serialization support #1512 — DOMException serde support
This PR — FatalError and RetryableError serde
Serialize thrown step errors through the devalue pipeline (event log format change)
Serialize thrown workflow errors through the devalue pipeline

Design

Rather than adding explicit reducer/reviver entries to the serialization pipeline (the approach in PRs 1-2 for built-in JS types), FatalError and RetryableError use the custom class serialization flow — the same mechanism user-defined classes use:

The classes declare static [WORKFLOW_SERIALIZE]() and static [WORKFLOW_DESERIALIZE]() methods
The SWC plugin discovers these during build and generates classId + registration IIFEs in each bundle context (step, workflow, client)
The existing Instance reducer/reviver handles serialization and deserialization automatically
Cross-VM behavior is correct: each bundle context registers its own class reference, so instanceof works in all contexts

This is the right approach because:

FatalError and RetryableError are not global constructors (unlike TypeError, DOMException) — they're named exports from @workflow/errors
The SWC plugin already handles discovery of serde symbols on imported classes
No changes needed to @workflow/core's serialization pipeline — the Instance flow handles everything

Test plan

6 new unit tests in serialization.test.ts verifying round-trip serialization for both classes (type preservation, stack, retryAfter, Instance serialization key)
2 new e2e workflow tests in 99_e2e.ts + e2e.test.ts verifying class identity preservation (instanceof, FatalError.is(), custom properties) through the full step → workflow error boundary
All 525 core package unit tests pass
Both packages build cleanly with tsc

Note: The e2e tests require a running dev server with the SWC plugin active to validate the full discovery → registration → serialization → deserialization pipeline.

changeset-bot · 2026-03-24T21:57:05Z

🦋 Changeset detected

Latest commit: 728d056

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

This PR includes changesets to release 20 packages

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

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

vercel · 2026-03-24T21:57:06Z

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
example-nextjs-workflow-turbopack	Ready	Preview, Comment	Apr 6, 2026 6:03am
example-nextjs-workflow-webpack	Ready	Preview, Comment	Apr 6, 2026 6:03am
example-workflow	Ready	Preview, Comment	Apr 6, 2026 6:03am
workbench-astro-workflow	Ready	Preview, Comment	Apr 6, 2026 6:03am
workbench-express-workflow	Ready	Preview, Comment	Apr 6, 2026 6:03am
workbench-fastify-workflow	Ready	Preview, Comment	Apr 6, 2026 6:03am
workbench-hono-workflow	Ready	Preview, Comment	Apr 6, 2026 6:03am
workbench-nitro-workflow	Ready	Preview, Comment	Apr 6, 2026 6:03am
workbench-nuxt-workflow	Ready	Preview, Comment	Apr 6, 2026 6:03am
workbench-sveltekit-workflow	Ready	Preview, Comment	Apr 6, 2026 6:03am
workbench-vite-workflow	Ready	Preview, Comment	Apr 6, 2026 6:03am
workflow-docs	Ready	Preview, Comment, Open in v0	Apr 6, 2026 6:03am
workflow-swc-playground	Ready	Preview, Comment	Apr 6, 2026 6:03am

github-actions · 2026-03-24T21:57:12Z

🧪 E2E Test Results

❌ Some tests failed

Summary

	Passed	Failed	Skipped	Total
❌ ▲ Vercel Production	868	22	67	957
❌ 💻 Local Development	782	22	153	957
❌ 📦 Local Production	842	24	178	1044
❌ 🐘 Local Postgres	842	24	178	1044
❌ 🪟 Windows	77	2	8	87
❌ 🌍 Community Worlds	134	67	24	225
❌ 📋 Other	213	6	42	261
Total	3758	167	650	4575

❌ Failed Tests

▲ Vercel Production (22 failed)

astro (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

example (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

express (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

fastify (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

hono (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

nextjs-turbopack (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

nextjs-webpack (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

nitro (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

nuxt (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

sveltekit (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

vite (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

💻 Local Development (22 failed)

astro-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

express-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

fastify-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

hono-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

nextjs-turbopack-canary (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

nextjs-turbopack-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

nextjs-webpack-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

nitro-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

nuxt-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

sveltekit-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

vite-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

📦 Local Production (24 failed)

astro-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

express-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

fastify-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

hono-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

nextjs-turbopack-canary (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

nextjs-turbopack-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

nextjs-webpack-canary (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

nextjs-webpack-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

nitro-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

nuxt-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

sveltekit-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

vite-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

🐘 Local Postgres (24 failed)

astro-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

express-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

fastify-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

hono-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

nextjs-turbopack-canary (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

nextjs-turbopack-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

nextjs-webpack-canary (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

nextjs-webpack-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

nitro-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

nuxt-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

sveltekit-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

vite-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

🪟 Windows (2 failed)

nextjs-turbopack (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

🌍 Community Worlds (67 failed)

mongodb (5 failed):

hookWorkflow is not resumable via public webhook endpoint | wrun_01KNGP643DPJ3CMCR2Q53BCQBG
webhookWorkflow | wrun_01KNGP6D6VQQGGZEVAY7MF0QKA
error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization
concurrent hook token conflict - two workflows cannot use the same hook token simultaneously | wrun_01KNGPFPZYJ1CKYB76CP39WTD0

redis (4 failed):

hookWorkflow is not resumable via public webhook endpoint | wrun_01KNGP643DPJ3CMCR2Q53BCQBG
error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization
concurrent hook token conflict - two workflows cannot use the same hook token simultaneously | wrun_01KNGPFPZYJ1CKYB76CP39WTD0

turso (58 failed):

addTenWorkflow | wrun_01KNGP51680JYGAFY0D055VGE1
addTenWorkflow | wrun_01KNGP51680JYGAFY0D055VGE1
wellKnownAgentWorkflow (.well-known/agent) | wrun_01KNGP76SAMT0Y4K2SGS6DCP0B
should work with react rendering in step
promiseAllWorkflow | wrun_01KNGP57BZH2D25K3VAF2JJYVA
promiseRaceWorkflow | wrun_01KNGP5BNGXR2EHJEB0X7ZHQFT
promiseAnyWorkflow | wrun_01KNGP5DTCNCRCQ24KX3TEHFSH
importedStepOnlyWorkflow | wrun_01KNGP7K72V9RT3MWJXXRZZZYV
hookWorkflow | wrun_01KNGP5SW2SKHB3QWRJBY31K7X
hookWorkflow is not resumable via public webhook endpoint | wrun_01KNGP643DPJ3CMCR2Q53BCQBG
webhookWorkflow | wrun_01KNGP6D6VQQGGZEVAY7MF0QKA
sleepingWorkflow | wrun_01KNGP6KKJE5QX15SE9MBSVQKA
parallelSleepWorkflow | wrun_01KNGP6ZY8RVK7VXF5PD6MDP2M
nullByteWorkflow | wrun_01KNGP733G9X30PGAJV2VR8MKN
workflowAndStepMetadataWorkflow | wrun_01KNGP7548A4CCE173P8CSYF6N
fetchWorkflow | wrun_01KNGP9Q2FPHBD6CNF6BD28PWX
promiseRaceStressTestWorkflow | wrun_01KNGP9T7GDA3JMHQFAYTADTD8
error handling error propagation workflow errors nested function calls preserve message and stack trace
error handling error propagation workflow errors cross-file imports preserve message and stack trace
error handling error propagation step errors basic step error preserves message and stack trace
error handling error propagation step errors cross-file step error preserves message and function names in stack
error handling retry behavior regular Error retries until success
error handling retry behavior FatalError fails immediately without retries
error handling retry behavior RetryableError respects custom retryAfter delay
error handling retry behavior maxRetries=0 disables retries
error handling catchability FatalError can be caught and detected with FatalError.is()
error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization
error handling not registered WorkflowNotRegisteredError fails the run when workflow does not exist
error handling not registered StepNotRegisteredError fails the step but workflow can catch it
error handling not registered StepNotRegisteredError fails the run when not caught in workflow
hookCleanupTestWorkflow - hook token reuse after workflow completion | wrun_01KNGPF3KHPNDHV9EPGYDJ9ZVT
concurrent hook token conflict - two workflows cannot use the same hook token simultaneously | wrun_01KNGPFPZYJ1CKYB76CP39WTD0
hookDisposeTestWorkflow - hook token reuse after explicit disposal while workflow still running | wrun_01KNGPGAXRCQ26RY23K637688D
stepFunctionPassingWorkflow - step function references can be passed as arguments (without closure vars) | wrun_01KNGPGXK21KVKJ9M10RWCBFT9
stepFunctionWithClosureWorkflow - step function with closure variables passed as argument | wrun_01KNGPH5Y4R55DR69DKMF61XVK
closureVariableWorkflow - nested step functions with closure variables | wrun_01KNGPHB1PKQYG1XGW5NNGD6ZZ
spawnWorkflowFromStepWorkflow - spawning a child workflow using start() inside a step | wrun_01KNGPHD6A0T5A4CTDYG7FGZ8S
health check (queue-based) - workflow and step endpoints respond to health check messages
pathsAliasWorkflow - TypeScript path aliases resolve correctly | wrun_01KNGPHV802XZH88XMZ1W1QR45
Calculator.calculate - static workflow method using static step methods from another class | wrun_01KNGPJ08J1BE3VQ2WWK1JW3TD
AllInOneService.processNumber - static workflow method using sibling static step methods | wrun_01KNGPJ5CKYNQ8ME49545P2BJJ
ChainableService.processWithThis - static step methods using this to reference the class | wrun_01KNGPJCJNFXP4N9RXFN5HPEB8
thisSerializationWorkflow - step function invoked with .call() and .apply() | wrun_01KNGPJHNZ027S5BGA91G51P9R
customSerializationWorkflow - custom class serialization with WORKFLOW_SERIALIZE/WORKFLOW_DESERIALIZE | wrun_01KNGPJS2AKVSJVJQRTRR5DD65
instanceMethodStepWorkflow - instance methods with "use step" directive | wrun_01KNGPJZ5ZJAGHEN233Z12HYZN
crossContextSerdeWorkflow - classes defined in step code are deserializable in workflow context | wrun_01KNGPK9KYZJ1F0VQH686B3QRF
stepFunctionAsStartArgWorkflow - step function reference passed as start() argument | wrun_01KNGPKH4AK532YHCXP9GYP1PV
cancelRun - cancelling a running workflow | wrun_01KNGPKQA6JDJTSDKPF5A2CFQV
cancelRun via CLI - cancelling a running workflow | wrun_01KNGPM0CFA2SYDCVQH461CQHJ
pages router addTenWorkflow via pages router
pages router promiseAllWorkflow via pages router
pages router sleepingWorkflow via pages router
hookWithSleepWorkflow - hook payloads delivered correctly with concurrent sleep | wrun_01KNGPMBV1PPN1GTT87BRNPQFT
sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_01KNGPMZ64S88DCWHR8TZAHJBZ
sleepWithSequentialStepsWorkflow - sequential steps work with concurrent sleep (control) | wrun_01KNGPN95C7JAN3TTB3E1B4ETB
importMetaUrlWorkflow - import.meta.url is available in step bundles | wrun_01KNGPNFG3HV8TKQKZYB4FNZTZ
metadataFromHelperWorkflow - getWorkflowMetadata/getStepMetadata work from module-level helper (#1577) | wrun_01KNGPNHHZKJCV399VXKAV9ZRC

📋 Other (6 failed)

e2e-local-dev-nest-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

e2e-local-postgres-nest-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

e2e-local-prod-nest-stable (2 failed):

error handling catchability FatalError preserves class identity through serialization
error handling catchability RetryableError preserves class identity through serialization

Details by Category

❌ ▲ Vercel Production

App	Passed	Failed	Skipped
❌ astro	78	2	7
❌ example	78	2	7
❌ express	78	2	7
❌ fastify	78	2	7
❌ hono	78	2	7
❌ nextjs-turbopack	83	2	2
❌ nextjs-webpack	83	2	2
❌ nitro	78	2	7
❌ nuxt	78	2	7
❌ sveltekit	78	2	7
❌ vite	78	2	7

❌ 💻 Local Development

App	Passed	Failed	Skipped
❌ astro-stable	71	2	14
❌ express-stable	71	2	14
❌ fastify-stable	71	2	14
❌ hono-stable	71	2	14
❌ nextjs-turbopack-canary	60	2	25
❌ nextjs-turbopack-stable	77	2	8
❌ nextjs-webpack-stable	77	2	8
❌ nitro-stable	71	2	14
❌ nuxt-stable	71	2	14
❌ sveltekit-stable	71	2	14
❌ vite-stable	71	2	14

❌ 📦 Local Production

App	Passed	Failed	Skipped
❌ astro-stable	71	2	14
❌ express-stable	71	2	14
❌ fastify-stable	71	2	14
❌ hono-stable	71	2	14
❌ nextjs-turbopack-canary	60	2	25
❌ nextjs-turbopack-stable	77	2	8
❌ nextjs-webpack-canary	60	2	25
❌ nextjs-webpack-stable	77	2	8
❌ nitro-stable	71	2	14
❌ nuxt-stable	71	2	14
❌ sveltekit-stable	71	2	14
❌ vite-stable	71	2	14

❌ 🐘 Local Postgres

App	Passed	Failed	Skipped
❌ astro-stable	71	2	14
❌ express-stable	71	2	14
❌ fastify-stable	71	2	14
❌ hono-stable	71	2	14
❌ nextjs-turbopack-canary	60	2	25
❌ nextjs-turbopack-stable	77	2	8
❌ nextjs-webpack-canary	60	2	25
❌ nextjs-webpack-stable	77	2	8
❌ nitro-stable	71	2	14
❌ nuxt-stable	71	2	14
❌ sveltekit-stable	71	2	14
❌ vite-stable	71	2	14

❌ 🪟 Windows

App	Passed	Failed	Skipped
❌ nextjs-turbopack	77	2	8

❌ 🌍 Community Worlds

App	Passed	Failed	Skipped
✅ mongodb-dev	5	0	0
❌ mongodb	57	5	8
✅ redis-dev	5	0	0
❌ redis	58	4	8
✅ turso-dev	5	0	0
❌ turso	4	58	8

❌ 📋 Other

App	Passed	Failed	Skipped
❌ e2e-local-dev-nest-stable	71	2	14
❌ e2e-local-postgres-nest-stable	71	2	14
❌ e2e-local-prod-nest-stable	71	2	14

📋 View full workflow run

❌ Some E2E test jobs failed:

Vercel Prod: failure
Local Dev: failure
Local Prod: failure
Local Postgres: failure
Windows: failure

Check the workflow run for details.

Copilot

Pull request overview

Adds first-class devalue serialization support for Workflow DevKit error types FatalError and RetryableError, improving type preservation across serialization boundaries.

Changes:

Add FatalError / RetryableError reducers and revivers to the common devalue pipeline.
Extend serialization tests with new round-trip coverage for both error types and adjust cross-VM FatalError expectations.
Add a changeset to release the update as a patch to @workflow/core.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
packages/core/src/serialization.ts	Introduces new special reducers/revivers for `FatalError` and `RetryableError` in the common serialization pipeline.
packages/core/src/serialization.test.ts	Updates cross-VM FatalError assertions and adds new round-trip tests for Fatal/Retryable errors.
.changeset/fatal-retryable-error-serialization.md	Declares a patch release note for the new serialization behavior.

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

Copilot · 2026-03-24T22:02:21Z

+      if (!FatalError.is(value)) return false;
+      return {
+        message: value.message,
+        stack: value.stack,


FatalError currently serializes only {message, stack}. Since this reducer runs before the generic Error reducer, any FatalError with an assigned cause will now lose its cause chain during serialization/deserialization. Consider including cause in the serialized payload and restoring it on the revived error (e.g., assign error.cause when present).

Suggested change

stack: value.stack,

stack: value.stack,

// Preserve the error cause chain when present

cause: (value as any).cause,

Copilot · 2026-03-24T22:02:22Z

+      return {
+        message: value.message,
+        stack: value.stack,
+        retryAfter: (value as RetryableError).retryAfter,


RetryableError reducer assumes retryAfter exists and is a Date from the same realm. Since RetryableError.is() only checks value.name, any Error named 'RetryableError' without a valid date-like retryAfter can be captured and cause hydration to throw. Additionally, when serializing across VM realms, retryAfter may be a host-realm Date that fails the Date reducer’s instanceof global.Date check, so it won’t be revived as a Date. Add validation that retryAfter is date-like and normalize it to a global.Date (or serialize it as an ISO string) before returning it; otherwise return false to fall back to the generic Error reducer. Also consider serializing/restoring cause here to avoid regressing from the generic Error reducer’s cause preservation.

Suggested change

return {

message: value.message,

stack: value.stack,

retryAfter: (value as RetryableError).retryAfter,

const retryAfterRaw = (value as RetryableError).retryAfter as unknown;

let timestamp: number | null = null;

if (

retryAfterRaw &&

typeof retryAfterRaw === 'object' &&

typeof (retryAfterRaw as { getTime?: unknown }).getTime === 'function'

) {

const t = (retryAfterRaw as Date).getTime();

if (!Number.isNaN(t)) timestamp = t;

} else if (

typeof retryAfterRaw === 'string' ||

typeof retryAfterRaw === 'number'

) {

const t = new Date(retryAfterRaw).getTime();

if (!Number.isNaN(t)) timestamp = t;

}

if (timestamp === null) {

// Not a valid date-like retryAfter; fall back to generic Error reducer.

return false;

}

const retryAfter = new Date(timestamp);

const cause =

'cause' in (value as Error) ? (value as Error & { cause?: unknown }).cause : undefined;

return {

message: value.message,

stack: value.stack,

retryAfter,

...(cause !== undefined ? { cause } : {}),

Copilot · 2026-03-24T22:02:22Z

+      // Use the context-specific FatalError if available (e.g. workflow VM),
+      // otherwise fall back to a plain Error with the FatalError name.
+      // This ensures the deserialized error is instanceof the correct context's Error.


The FatalError reviver comment says it falls back to a plain Error and that this guarantees instanceof the context's Error. The implementation actually falls back to the imported host FatalError class, which may be from a different realm than global.Error. Please update the comment to match the behavior (context ctor if provided; otherwise host ctor, and rely on FatalError.is() for cross-realm checks).

Suggested change

// Use the context-specific FatalError if available (e.g. workflow VM),

// otherwise fall back to a plain Error with the FatalError name.

// This ensures the deserialized error is instanceof the correct context's Error.

// Prefer the context-specific FatalError constructor if available (e.g. workflow VM),

// otherwise fall back to the imported host FatalError constructor.

// Cross-realm identification should rely on FatalError.is() rather than instanceof.

vercel · 2026-04-02T00:27:12Z

+/** Test: RetryableError preserves class identity through step error serialization */
+async function throwRetryableErrorStep() {
+  'use step';
+  throw new RetryableError('retryable serde test', {


The errorRetryableSerdeRoundTrip e2e test will always time out because it throws a RetryableError with retryAfter set to year 2099 (causing ~74-year retry delay), and even if retries were exhausted, the step_failed path always reconstructs the error as FatalError (not RetryableError), causing all test assertions to fail.

- Pass DOMException through to the workflow VM context alongside other Web APIs (Headers, URL, TextEncoder, etc.) - Add DOMException reducer/reviver to the serialization pipeline, preserving message, name, derived code, and cause when present - Add DOMException to the Serializable type union - 8 new tests: round-trip for AbortError, NotFoundError, default name, cause preservation, cause absence, serialization key, cross-VM boundaries, and VM context availability

…leError Add custom serialization methods to FatalError and RetryableError in @workflow/errors, enabling the SWC plugin to discover and register them through the standard class serialization pipeline. This preserves class identity (instanceof), the fatal flag, and the retryAfter date when these errors cross serialization boundaries. - Add @workflow/serde dependency to @workflow/errors - Add WORKFLOW_SERIALIZE/WORKFLOW_DESERIALIZE static methods to both classes - Add unit tests verifying Instance-based round-trip serialization - Add e2e workflow tests verifying class identity preservation end-to-end

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Add first-class serialization for FatalError and RetryableError#1513

Add first-class serialization for FatalError and RetryableError#1513
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nrajlich/error-class-serde

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-      return {
-        message: value.message,
-        stack: value.stack,
-        retryAfter: (value as RetryableError).retryAfter,
+      const retryAfterRaw = (value as RetryableError).retryAfter as unknown;
+      let timestamp: number | null = null;
+      if (
+        retryAfterRaw &&
+        typeof retryAfterRaw === 'object' &&
+        typeof (retryAfterRaw as { getTime?: unknown }).getTime === 'function'
+      ) {
+        const t = (retryAfterRaw as Date).getTime();
+        if (!Number.isNaN(t)) timestamp = t;
+      } else if (
+        typeof retryAfterRaw === 'string' ||
+        typeof retryAfterRaw === 'number'
+      ) {
+        const t = new Date(retryAfterRaw).getTime();
+        if (!Number.isNaN(t)) timestamp = t;
+      }
+      if (timestamp === null) {
+        // Not a valid date-like retryAfter; fall back to generic Error reducer.
+        return false;
+      }
+      const retryAfter = new Date(timestamp);
+      const cause =
+        'cause' in (value as Error) ? (value as Error & { cause?: unknown }).cause : undefined;
+      return {
+        message: value.message,
+        stack: value.stack,
+        retryAfter,
+        ...(cause !== undefined ? { cause } : {}),

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