core: make account login upgrades safe while adding multi-account workspace auth (#15487)

Co-authored-by: Kit Langton <kit.langton@gmail.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

packages/opencode/test/fixture/effect.ts

@@ -0,0 +1,7 @@
+import { test } from "bun:test"
+import { Effect, Layer } from "effect"
+
+export const testEffect = <R, E>(layer: Layer.Layer<R, E, never>) => ({
+  effect: <A, E2>(name: string, value: Effect.Effect<A, E2, R>) =>
+    test(name, () => Effect.runPromise(value.pipe(Effect.provide(layer)))),
+})