effect-fiber

Use Effect.forkChild to attach a fiber to the parent, Effect.forkScoped or Effect.forkIn to tie it to a Scope, or Effect.forkDetach for fully detached work. The v3 names Effect.fork and Effect.forkDaemon no longer exist in v4.

FiberHandle supervises at most one fiber with latest-wins replacement, FiberMap manages keyed fibers where a new run under an existing key interrupts the previous one, and FiberSet is a grow-only collection with no replacement semantics. All three interrupt their fibers when the owning scope closes.

Fibers forked with Effect.forkChild are interrupted when the parent fiber completes, so fire-and-forget children die early. Use forkScoped for scope-tied work, forkDetach for detached work, or Effect.awaitAllChildren to wait for children.

No, Fiber.await always succeeds and returns the fiber's Exit for inspection. Use Fiber.join to propagate the fiber's failure into the current fiber, or inspect the Exit with Exit.isSuccess and Cause helpers.

Run each task through a FiberHandle, which interrupts the previous fiber whenever a new effect is run into it. FiberHandle.runtime returns a synchronous runner function suitable for event handlers like input listeners.

A bare runFork fiber suspended on a pure Effect primitive does not keep the Node.js process alive, since per-fiber keep-alive was removed from the core runtime. Use NodeRuntime.runMain, which installs a keep-alive timer plus SIGINT/SIGTERM handling and exit-code mapping.