perf: make vcs init non-blocking by forking git branch resolution (#22771)

Author: thdxr

packages/opencode/AGENTS.md

@@ -39,6 +39,12 @@ See `specs/effect/migration.md` for the compact pattern reference and examples.
 - 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.
+- To make a service's `init()` non-blocking, fork `InstanceState.get(state)` at the `init()` call site (e.g. `Effect.forkIn(scope)`), not by forking work inside the `InstanceState.make` closure. Forking inside the closure leaves state incomplete for other methods that read it.
+- `src/project/bootstrap.ts` already wraps every service `init()` in `Effect.forkDetach`, so `init()` is fire-and-forget in production. Keep `init()` methods synchronous internally; the caller controls concurrency.
+
+## Effect v4 beta API
+
+- `Effect.fork` and `Effect.forkDaemon` do not exist. Use `Effect.forkIn(scope)` to fork a fiber into a specific scope.
 
 ## Preferred Effect services
 

packages/opencode/src/project/vcs.ts

@@ -1,4 +1,4 @@
-import { Effect, Layer, Context, Stream } from "effect"
+import { Effect, Layer, Context, Stream, Scope } from "effect"
 import { formatPatch, structuredPatch } from "diff"
 import path from "path"
 import { Bus } from "@/bus"
@@ -157,6 +157,7 @@ export const layer: Layer.Layer<Service, never, AppFileSystem.Service | Git.Serv
     const fs = yield* AppFileSystem.Service
     const git = yield* Git.Service
     const bus = yield* Bus.Service
+    const scope = yield* Scope.Scope
 
     const state = yield* InstanceState.make<State>(
       Effect.fn("Vcs.state")(function* (ctx) {
@@ -194,7 +195,7 @@ export const layer: Layer.Layer<Service, never, AppFileSystem.Service | Git.Serv
 
     return Service.of({
       init: Effect.fn("Vcs.init")(function* () {
-        yield* InstanceState.get(state)
+        yield* InstanceState.get(state).pipe(Effect.forkIn(scope))
       }),
       branch: Effect.fn("Vcs.branch")(function* () {
         return yield* InstanceState.use(state, (x) => x.current)