diff --git a/packages/opencode/src/project/instance.ts b/packages/opencode/src/project/instance.ts
index df44a3a229c..425dc6611b1 100644
--- a/packages/opencode/src/project/instance.ts
+++ b/packages/opencode/src/project/instance.ts
@@ -1,3 +1,4 @@
+import { Effect } from "effect"
 import { Log } from "@/util/log"
 import { Context } from "../util/context"
 import { Project } from "./project"
@@ -5,6 +6,7 @@ import { State } from "./state"
 import { iife } from "@/util/iife"
 import { GlobalBus } from "@/bus/global"
 import { Filesystem } from "@/util/filesystem"
+import * as InstanceState from "@/util/instance-state"
 
 interface Context {
   directory: string
@@ -106,7 +108,7 @@ export const Instance = {
   async reload(input: { directory: string; init?: () => Promise<any>; project?: Project.Info; worktree?: string }) {
     const directory = Filesystem.resolve(input.directory)
     Log.Default.info("reloading instance", { directory })
-    await State.dispose(directory)
+    await Promise.all([State.dispose(directory), Effect.runPromise(InstanceState.dispose(directory))])
     cache.delete(directory)
     const next = track(directory, boot({ ...input, directory }))
     emit(directory)
@@ -114,7 +116,7 @@ export const Instance = {
   },
   async dispose() {
     Log.Default.info("disposing instance", { directory: Instance.directory })
-    await State.dispose(Instance.directory)
+    await Promise.all([State.dispose(Instance.directory), Effect.runPromise(InstanceState.dispose(Instance.directory))])
     cache.delete(Instance.directory)
     emit(Instance.directory)
   },
diff --git a/packages/opencode/src/provider/auth-service.ts b/packages/opencode/src/provider/auth-service.ts
index a97ce1840c6..951a1dba483 100644
--- a/packages/opencode/src/provider/auth-service.ts
+++ b/packages/opencode/src/provider/auth-service.ts
@@ -1,23 +1,14 @@
-import { Effect, Layer, ServiceMap } from "effect"
+import { Effect, Layer, Record, ServiceMap, Struct } from "effect"
 import { Instance } from "@/project/instance"
 import { Plugin } from "../plugin"
-import { filter, fromEntries, map, mapValues, pipe } from "remeda"
+import { filter, fromEntries, map, pipe } from "remeda"
 import type { AuthOuathResult } from "@opencode-ai/plugin"
 import { NamedError } from "@opencode-ai/util/error"
 import * as Auth from "@/auth/service"
+import * as InstanceState from "@/util/instance-state"
 import { ProviderID } from "./schema"
 import z from "zod"
 
-const state = Instance.state(async () => {
-  const methods = pipe(
-    await Plugin.list(),
-    filter((x) => x.auth?.provider !== undefined),
-    map((x) => [x.auth!.provider, x.auth!] as const),
-    fromEntries(),
-  )
-  return { methods, pending: {} as Record<string, AuthOuathResult> }
-})
-
 export type Method = {
   type: "oauth" | "api"
   label: string
@@ -53,13 +44,20 @@ export type ProviderAuthError =
 
 export namespace ProviderAuthService {
   export interface Service {
+    /** Get available auth methods for each provider (e.g. OAuth, API key). */
     readonly methods: () => Effect.Effect<Record<string, Method[]>>
+
+    /** Start an OAuth authorization flow for a provider. Returns the URL to redirect to. */
     readonly authorize: (input: { providerID: ProviderID; method: number }) => Effect.Effect<Authorization | undefined>
+
+    /** Complete an OAuth flow after the user has authorized. Exchanges the code/callback for credentials. */
     readonly callback: (input: {
       providerID: ProviderID
       method: number
       code?: string
     }) => Effect.Effect<void, ProviderAuthError>
+
+    /** Set an API key directly for a provider (no OAuth flow). */
     readonly api: (input: { providerID: ProviderID; key: string }) => Effect.Effect<void, Auth.AuthServiceError>
   }
 }
@@ -71,35 +69,35 @@ export class ProviderAuthService extends ServiceMap.Service<ProviderAuthService,
     ProviderAuthService,
     Effect.gen(function* () {
       const auth = yield* Auth.AuthService
+      const state = yield* InstanceState.make({
+        lookup: () =>
+          Effect.promise(async () => {
+            const methods = pipe(
+              await Plugin.list(),
+              filter((x) => x.auth?.provider !== undefined),
+              map((x) => [x.auth!.provider, x.auth!] as const),
+              fromEntries(),
+            )
+            return { methods, pending: {} as Record<string, AuthOuathResult> }
+          }),
+      })
 
-      const methods = Effect.fn("ProviderAuthService.methods")(() =>
-        Effect.promise(() =>
-          state().then((x) =>
-            mapValues(x.methods, (y) =>
-              y.methods.map(
-                (z): Method => ({
-                  type: z.type,
-                  label: z.label,
-                }),
-              ),
-            ),
-          ),
-        ),
-      )
+      const methods = Effect.fn("ProviderAuthService.methods")(function* () {
+        const x = yield* InstanceState.get(state)
+        return Record.map(x.methods, (y) => y.methods.map((z): Method => Struct.pick(z, ["type", "label"])))
+      })
 
       const authorize = Effect.fn("ProviderAuthService.authorize")(function* (input: {
         providerID: ProviderID
         method: number
       }) {
-        const item = yield* Effect.promise(() => state().then((x) => x.methods[input.providerID]))
-        const method = item.methods[input.method]
+        const authHook = (yield* InstanceState.get(state)).methods[input.providerID]
+        const method = authHook.methods[input.method]
         if (method.type !== "oauth") return
         const result = yield* Effect.promise(() => method.authorize())
-        yield* Effect.promise(() =>
-          state().then((x) => {
-            x.pending[input.providerID] = result
-          }),
-        )
+
+        const s = yield* InstanceState.get(state)
+        s.pending[input.providerID] = result
         return {
           url: result.url,
           method: result.method,
@@ -112,17 +110,15 @@ export class ProviderAuthService extends ServiceMap.Service<ProviderAuthService,
         method: number
         code?: string
       }) {
-        const match = yield* Effect.promise(() => state().then((x) => x.pending[input.providerID]))
+        const match = (yield* InstanceState.get(state)).pending[input.providerID]
         if (!match) return yield* Effect.fail(new OauthMissing({ providerID: input.providerID }))
 
-        const result =
-          match.method === "code"
-            ? yield* Effect.gen(function* () {
-                const code = input.code
-                if (!code) return yield* Effect.fail(new OauthCodeMissing({ providerID: input.providerID }))
-                return yield* Effect.promise(() => match.callback(code))
-              })
-            : yield* Effect.promise(() => match.callback())
+        if (match.method === "code" && !input.code)
+          return yield* Effect.fail(new OauthCodeMissing({ providerID: input.providerID }))
+
+        const result = yield* Effect.promise(() =>
+          match.method === "code" ? match.callback(input.code!) : match.callback(),
+        )
 
         if (!result || result.type !== "success") return yield* Effect.fail(new OauthCallbackFailed({}))
 
diff --git a/packages/opencode/src/provider/auth.ts b/packages/opencode/src/provider/auth.ts
index bc53d874c4c..d513085392e 100644
--- a/packages/opencode/src/provider/auth.ts
+++ b/packages/opencode/src/provider/auth.ts
@@ -5,6 +5,9 @@ import { fn } from "@/util/fn"
 import * as S from "./auth-service"
 import { ProviderID } from "./schema"
 
+// Separate runtime: ProviderAuthService can't join the shared runtime because
+// runtime.ts → auth-service.ts → provider/auth.ts creates a circular import.
+// AuthService is stateless file I/O so the duplicate instance is harmless.
 const rt = ManagedRuntime.make(S.ProviderAuthService.defaultLayer)
 
 function runPromise<A>(f: (service: S.ProviderAuthService.Service) => Effect.Effect<A, S.ProviderAuthError>) {
diff --git a/packages/opencode/src/util/instance-state.ts b/packages/opencode/src/util/instance-state.ts
new file mode 100644
index 00000000000..7d6a6d9768d
--- /dev/null
+++ b/packages/opencode/src/util/instance-state.ts
@@ -0,0 +1,48 @@
+import { Effect, ScopedCache, Scope } from "effect"
+
+import { Instance } from "@/project/instance"
+
+const TypeId = Symbol.for("@opencode/InstanceState")
+
+type Task = (key: string) => Effect.Effect<void>
+
+const tasks = new Set<Task>()
+
+export interface InstanceState<A, E = never, R = never> {
+  readonly [TypeId]: typeof TypeId
+  readonly cache: ScopedCache.ScopedCache<string, A, E, R>
+}
+
+export const make = <A, E = never, R = never>(input: {
+  lookup: (key: string) => Effect.Effect<A, E, R>
+  release?: (value: A, key: string) => Effect.Effect<void>
+}): Effect.Effect<InstanceState<A, E, R>, never, R | Scope.Scope> =>
+  Effect.gen(function* () {
+    const cache = yield* ScopedCache.make<string, A, E, R>({
+      capacity: Number.POSITIVE_INFINITY,
+      lookup: (key) =>
+        Effect.acquireRelease(input.lookup(key), (value) => (input.release ? input.release(value, key) : Effect.void)),
+    })
+
+    const task: Task = (key) => ScopedCache.invalidate(cache, key)
+    tasks.add(task)
+    yield* Effect.addFinalizer(() => Effect.sync(() => void tasks.delete(task)))
+
+    return {
+      [TypeId]: TypeId,
+      cache,
+    }
+  })
+
+export const get = <A, E, R>(self: InstanceState<A, E, R>) => ScopedCache.get(self.cache, Instance.directory)
+
+export const has = <A, E, R>(self: InstanceState<A, E, R>) => ScopedCache.has(self.cache, Instance.directory)
+
+export const invalidate = <A, E, R>(self: InstanceState<A, E, R>) =>
+  ScopedCache.invalidate(self.cache, Instance.directory)
+
+export const dispose = (key: string) =>
+  Effect.all(
+    [...tasks].map((task) => task(key)),
+    { concurrency: "unbounded" },
+  )
diff --git a/packages/opencode/test/project/state.test.ts b/packages/opencode/test/project/state.test.ts
new file mode 100644
index 00000000000..314343d671c
--- /dev/null
+++ b/packages/opencode/test/project/state.test.ts
@@ -0,0 +1,87 @@
+import { expect, test } from "bun:test"
+
+import { State } from "../../src/project/state"
+
+test("State.create caches values for the same key", async () => {
+  let key = "a"
+  let n = 0
+  const state = State.create(
+    () => key,
+    () => ({ n: ++n }),
+  )
+
+  const a = state()
+  const b = state()
+
+  expect(a).toBe(b)
+  expect(n).toBe(1)
+
+  await State.dispose("a")
+})
+
+test("State.create isolates values by key", async () => {
+  let key = "a"
+  let n = 0
+  const state = State.create(
+    () => key,
+    () => ({ n: ++n }),
+  )
+
+  const a = state()
+  key = "b"
+  const b = state()
+  key = "a"
+  const c = state()
+
+  expect(a).toBe(c)
+  expect(a).not.toBe(b)
+  expect(n).toBe(2)
+
+  await State.dispose("a")
+  await State.dispose("b")
+})
+
+test("State.dispose clears a key and runs cleanup", async () => {
+  const seen: string[] = []
+  let key = "a"
+  let n = 0
+  const state = State.create(
+    () => key,
+    () => ({ n: ++n }),
+    async (value) => {
+      seen.push(String(value.n))
+    },
+  )
+
+  const a = state()
+  await State.dispose("a")
+  const b = state()
+
+  expect(a).not.toBe(b)
+  expect(seen).toEqual(["1"])
+
+  await State.dispose("a")
+})
+
+test("State.create dedupes concurrent promise initialization", async () => {
+  const gate = Promise.withResolvers<void>()
+  let n = 0
+  const state = State.create(
+    () => "a",
+    async () => {
+      n += 1
+      await gate.promise
+      return { n }
+    },
+  )
+
+  const task = Promise.all([state(), state()])
+  await Promise.resolve()
+  expect(n).toBe(1)
+
+  gate.resolve()
+  const [a, b] = await task
+  expect(a).toBe(b)
+
+  await State.dispose("a")
+})
diff --git a/packages/opencode/test/util/instance-state.test.ts b/packages/opencode/test/util/instance-state.test.ts
new file mode 100644
index 00000000000..bd2df4bbf64
--- /dev/null
+++ b/packages/opencode/test/util/instance-state.test.ts
@@ -0,0 +1,139 @@
+import { afterEach, expect, test } from "bun:test"
+import { Effect } from "effect"
+
+import { Instance } from "../../src/project/instance"
+import * as InstanceState from "../../src/util/instance-state"
+import { tmpdir } from "../fixture/fixture"
+
+async function access<A, E>(state: InstanceState.InstanceState<A, E>, dir: string) {
+  return Instance.provide({
+    directory: dir,
+    fn: () => Effect.runPromise(InstanceState.get(state)),
+  })
+}
+
+afterEach(async () => {
+  await Instance.disposeAll()
+})
+
+test("InstanceState caches values for the same instance", async () => {
+  await using tmp = await tmpdir()
+  let n = 0
+
+  await Effect.runPromise(
+    Effect.scoped(
+      Effect.gen(function* () {
+        const state = yield* InstanceState.make({
+          lookup: () => Effect.sync(() => ({ n: ++n })),
+        })
+
+        const a = yield* Effect.promise(() => access(state, tmp.path))
+        const b = yield* Effect.promise(() => access(state, tmp.path))
+
+        expect(a).toBe(b)
+        expect(n).toBe(1)
+      }),
+    ),
+  )
+})
+
+test("InstanceState isolates values by directory", async () => {
+  await using a = await tmpdir()
+  await using b = await tmpdir()
+  let n = 0
+
+  await Effect.runPromise(
+    Effect.scoped(
+      Effect.gen(function* () {
+        const state = yield* InstanceState.make({
+          lookup: (dir) => Effect.sync(() => ({ dir, n: ++n })),
+        })
+
+        const x = yield* Effect.promise(() => access(state, a.path))
+        const y = yield* Effect.promise(() => access(state, b.path))
+        const z = yield* Effect.promise(() => access(state, a.path))
+
+        expect(x).toBe(z)
+        expect(x).not.toBe(y)
+        expect(n).toBe(2)
+      }),
+    ),
+  )
+})
+
+test("InstanceState is disposed on instance reload", async () => {
+  await using tmp = await tmpdir()
+  const seen: string[] = []
+  let n = 0
+
+  await Effect.runPromise(
+    Effect.scoped(
+      Effect.gen(function* () {
+        const state = yield* InstanceState.make({
+          lookup: () => Effect.sync(() => ({ n: ++n })),
+          release: (value) =>
+            Effect.sync(() => {
+              seen.push(String(value.n))
+            }),
+        })
+
+        const a = yield* Effect.promise(() => access(state, tmp.path))
+        yield* Effect.promise(() => Instance.reload({ directory: tmp.path }))
+        const b = yield* Effect.promise(() => access(state, tmp.path))
+
+        expect(a).not.toBe(b)
+        expect(seen).toEqual(["1"])
+      }),
+    ),
+  )
+})
+
+test("InstanceState is disposed on disposeAll", async () => {
+  await using a = await tmpdir()
+  await using b = await tmpdir()
+  const seen: string[] = []
+
+  await Effect.runPromise(
+    Effect.scoped(
+      Effect.gen(function* () {
+        const state = yield* InstanceState.make({
+          lookup: (dir) => Effect.sync(() => ({ dir })),
+          release: (value) =>
+            Effect.sync(() => {
+              seen.push(value.dir)
+            }),
+        })
+
+        yield* Effect.promise(() => access(state, a.path))
+        yield* Effect.promise(() => access(state, b.path))
+        yield* Effect.promise(() => Instance.disposeAll())
+
+        expect(seen.sort()).toEqual([a.path, b.path].sort())
+      }),
+    ),
+  )
+})
+
+test("InstanceState dedupes concurrent lookups for the same directory", async () => {
+  await using tmp = await tmpdir()
+  let n = 0
+
+  await Effect.runPromise(
+    Effect.scoped(
+      Effect.gen(function* () {
+        const state = yield* InstanceState.make({
+          lookup: () =>
+            Effect.promise(async () => {
+              n += 1
+              await Bun.sleep(10)
+              return { n }
+            }),
+        })
+
+        const [a, b] = yield* Effect.promise(() => Promise.all([access(state, tmp.path), access(state, tmp.path)]))
+        expect(a).toBe(b)
+        expect(n).toBe(1)
+      }),
+    ),
+  )
+})