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In server component on the vercel world, get stuck awaiting workflow's run.returnValue despite the workflow returning #618
Description
In server component on the vercel world, get stuck awaiting workflow's run.returnValue despite the workflow returning
This happens in the vercel world but not in development:
Reproduction
A minimal repro can be found here:
https://github.com/remiconnesson/repro-workflow-vercel-rsc-await-return-value
// app/workflows/test-workflow.ts
import { sleep } from "workflow";
export async function testWorkflow(input: string) {
"use workflow";
console.log("[testWorkflow] 1. Started with:", input);
await sleep("2 seconds");
console.log("[testWorkflow] 2. After sleep");
return { message: `Hello ${input}`, timestamp: Date.now() };
}// app/page.tsx
import { start } from "workflow/api";
import { testWorkflow } from "@/app/workflows/test-workflow";
export const dynamic = "force-dynamic"; // otherwise can't deploy because the build hangs on await and times out
export default async function TestWorkflowPage() {
console.log("[TestPage] 1. Starting");
const run = await start(testWorkflow, ["world"]);
console.log("[TestPage] 2. Started, runId:", run.runId);
const status = await run.status;
console.log("[TestPage] 3. Status:", status);
console.log("[TestPage] 4. Awaiting returnValue...");
const result = await run.returnValue; // <-- ❌ code will not move past this point, will ultimately timeout
console.log("[TestPage] 5. Got result:", result);
return (
<div className="p-8">
<h1>Test Workflow Result</h1>
<pre>{JSON.stringify(result, null, 2)}</pre>
</div>
);
}Logs
✅ work in development
[TestPage] 1. Starting
[TestPage] 2. Started, runId: wrun_01KCJA3HBQNQ5NP7E092NQXSP1
[TestPage] 3. Status: pending
[TestPage] 4. Awaiting returnValue...
[testWorkflow] 1. Started with: world
POST /.well-known/workflow/v1/flow 503 in 66ms (compile: 3ms, render: 63ms)
[testWorkflow] 1. Started with: world
[testWorkflow] 2. After sleep
POST /.well-known/workflow/v1/flow 200 in 30ms (compile: 2ms, render: 28ms)
[TestPage] 5. Got result: { message: 'Hello world', timestamp: 1765846142391 }
GET / 200 in 3.1s (compile: 5ms, render: 3.1s)
❌ Fails in prod on vercel world
2025-12-16 00:50:41.201 [info] [TestPage] 1. Starting
2025-12-16 00:50:41.570 [info] [TestPage] 2. Started, runId: wrun_01KCJA6M2F8F2RSAXWYXZ3W754
2025-12-16 00:50:41.632 [info] [TestPage] 3. Status: pending
2025-12-16 00:50:41.632 [info] [TestPage] 4. Awaiting returnValue...
2025-12-16 00:50:41.903 [info] [testWorkflow] 1. Started with: world
2025-12-16 00:50:46.892 [info] [testWorkflow] 1. Started with: world
2025-12-16 00:50:46.894 [info] [testWorkflow] 2. After sleep
2025-12-16 00:55:40.884 [error] Vercel Runtime Timeout Error: Task timed out after 300 seconds
The workflow is marked as completed in the observability panel:
Activity
Fix RSC hang by replacing workflow with direct function call
remiconnesson commentedon Dec 16, 2025
I patched
@workflow/world-vercel/dist/utils.jsto log the results of the fetch util, suspecting that the result of the fetch call was being cached during the render of the RSC.We can see in the logs below that the reply always contain
status: 'pending'despite the workflow being finished.Patch of
@workflow/world-vercel/dist/utils.jsLogs from the workflow
Logs from the RSC
adriandlam commentedon Dec 17, 2025
hey @remiconnesson! thanks for the minimum repro, i believe it should be fixed in #639 but feel free to re-open if it isn't!
[world-vercel] Bust Next.js fetch cache on v4 event reads