- Use `makeRuntime` (from `src/effect/run-service.ts`) for all services. It returns `{ runPromise, runFork, runCallback }` backed by a shared `memoMap` that deduplicates layers.
- Use `InstanceState` (from `src/effect/instance-state.ts`) for per-directory or per-project state that needs per-instance cleanup. It uses `ScopedCache` keyed by directory — each open project gets its own state, automatically cleaned up on disposal.
- If two open directories should not share one copy of the service, it needs `InstanceState`.
- Do the work directly in the `InstanceState.make` closure — `ScopedCache` handles run-once semantics. Don't add fibers, `ensure()` callbacks, or `started` flags on top.
- Use `Effect.addFinalizer` or `Effect.acquireRelease` inside the `InstanceState.make` closure for cleanup (subscriptions, process teardown, etc.).
- Use `Effect.forkScoped` inside the closure for background stream consumers — the fiber is interrupted when the instance is disposed.
Use `Effect.cached` when multiple concurrent callers should share a single in-flight computation rather than storing `Fiber | undefined` or `Promise | undefined` manually. See `specs/effect-migration.md` for the full pattern.
Use it for native addon callbacks (`@parcel/watcher`, `node-pty`, native `fs.watch`, etc.) that need to call `Bus.publish` or anything that reads `Instance.directory`.