Effect fixes AsyncLocalStorage context leak in 3.20.0

Summary

Under production load, your auth checks could return the wrong user session or read cookies from in-flight requests. The bug is intermittent and hard to catch in testing, making it a silent security risk in any Effect app using AsyncLocalStorage-backed libraries like Clerk or Next.js App Router.

Why it matters

Under production load, your auth checks could return the wrong user session or read cookies from in-flight requests. The bug is intermittent and hard to catch in testing, making it a silent security risk in any Effect app using AsyncLocalStorage-backed libraries like Clerk or Next.js App Router.

Sources

1. 1.Under concurrent load, older Effect versions could resume fiber work under the wrong AsyncLocalStorage context.
2. 2.request-local state could be lost or, in the worst case, read from another in-flight request
3. 3.the scheduler now resumes them on a per-fiber basis. That preserves the correct async context boundary
4. 4.If your production system uses Effect with Clerk or similar libraries, treat this as a priority update.