diff --git a/packages/opencode/src/bus/index.ts b/packages/opencode/src/bus/index.ts
index edb093f197..5a1c106f4c 100644
--- a/packages/opencode/src/bus/index.ts
+++ b/packages/opencode/src/bus/index.ts
@@ -1,12 +1,13 @@
 import z from "zod"
+import { Effect, Layer, PubSub, ServiceMap, Stream } from "effect"
 import { Log } from "../util/log"
 import { Instance } from "../project/instance"
 import { BusEvent } from "./bus-event"
 import { GlobalBus } from "./global"
+import { runCallbackInstance, runPromiseInstance } from "../effect/runtime"
 
 export namespace Bus {
   const log = Log.create({ service: "bus" })
-  type Subscription = (event: any) => void
 
   export const InstanceDisposed = BusEvent.define(
     "server.instance.disposed",
@@ -15,91 +16,105 @@ export namespace Bus {
     }),
   )
 
-  const state = Instance.state(
-    () => {
-      const subscriptions = new Map<any, Subscription[]>()
+  // ---------------------------------------------------------------------------
+  // Service definition
+  // ---------------------------------------------------------------------------
 
-      return {
-        subscriptions,
+  type Payload<D extends BusEvent.Definition = BusEvent.Definition> = {
+    type: D["type"]
+    properties: z.infer<D["properties"]>
+  }
+
+  export interface Interface {
+    readonly publish: <D extends BusEvent.Definition>(
+      def: D,
+      properties: z.output<D["properties"]>,
+    ) => Effect.Effect<void>
+    readonly subscribe: <D extends BusEvent.Definition>(def: D) => Stream.Stream<Payload<D>>
+    readonly subscribeAll: () => Stream.Stream<Payload>
+  }
+
+  export class Service extends ServiceMap.Service<Service, Interface>()("@opencode/Bus") {}
+
+  export const layer = Layer.effect(
+    Service,
+    Effect.gen(function* () {
+      const pubsubs = new Map<string, PubSub.PubSub<Payload>>()
+      const wildcardPubSub = yield* PubSub.unbounded<Payload>()
+
+      const getOrCreate = Effect.fnUntraced(function* (type: string) {
+        let ps = pubsubs.get(type)
+        if (!ps) {
+          ps = yield* PubSub.unbounded<Payload>()
+          pubsubs.set(type, ps)
+        }
+        return ps
+      })
+
+      function publish<D extends BusEvent.Definition>(
+        def: D,
+        properties: z.output<D["properties"]>,
+      ) {
+        return Effect.gen(function* () {
+          const payload: Payload = { type: def.type, properties }
+          log.info("publishing", { type: def.type })
+
+          const ps = pubsubs.get(def.type)
+          if (ps) yield* PubSub.publish(ps, payload)
+          yield* PubSub.publish(wildcardPubSub, payload)
+
+          GlobalBus.emit("event", {
+            directory: Instance.directory,
+            payload,
+          })
+        })
       }
-    },
-    async (entry) => {
-      const wildcard = entry.subscriptions.get("*")
-      if (!wildcard) return
-      const event = {
-        type: InstanceDisposed.type,
-        properties: {
-          directory: Instance.directory,
-        },
+
+      function subscribe<D extends BusEvent.Definition>(def: D): Stream.Stream<Payload<D>> {
+        log.info("subscribing", { type: def.type })
+        return Stream.unwrap(
+          Effect.gen(function* () {
+            const ps = yield* getOrCreate(def.type)
+            return Stream.fromPubSub(ps) as Stream.Stream<Payload<D>>
+          }),
+        ).pipe(Stream.ensuring(Effect.sync(() => log.info("unsubscribing", { type: def.type }))))
       }
-      for (const sub of [...wildcard]) {
-        sub(event)
+
+      function subscribeAll(): Stream.Stream<Payload> {
+        log.info("subscribing", { type: "*" })
+        return Stream.fromPubSub(wildcardPubSub).pipe(
+          Stream.ensuring(Effect.sync(() => log.info("unsubscribing", { type: "*" }))),
+        )
       }
-    },
+
+      return Service.of({ publish, subscribe, subscribeAll })
+    }),
   )
 
-  export async function publish<Definition extends BusEvent.Definition>(
-    def: Definition,
-    properties: z.output<Definition["properties"]>,
-  ) {
-    const payload = {
-      type: def.type,
-      properties,
-    }
-    log.info("publishing", {
-      type: def.type,
-    })
-    const pending = []
-    for (const key of [def.type, "*"]) {
-      const match = state().subscriptions.get(key)
-      for (const sub of match ?? []) {
-        pending.push(sub(payload))
-      }
-    }
-    GlobalBus.emit("event", {
-      directory: Instance.directory,
-      payload,
-    })
-    return Promise.all(pending)
+  // ---------------------------------------------------------------------------
+  // Legacy adapters — plain function API wrapping the Effect service
+  // ---------------------------------------------------------------------------
+
+  function runStream(stream: (svc: Interface) => Stream.Stream<Payload>, callback: (event: any) => void) {
+    return runCallbackInstance(
+      Service.use((svc) =>
+        stream(svc).pipe(Stream.runForEach((msg) => Effect.sync(() => callback(msg)))),
+      ),
+    )
   }
 
-  export function subscribe<Definition extends BusEvent.Definition>(
-    def: Definition,
-    callback: (event: { type: Definition["type"]; properties: z.infer<Definition["properties"]> }) => void,
-  ) {
-    return raw(def.type, callback)
+  export function publish<D extends BusEvent.Definition>(def: D, properties: z.output<D["properties"]>) {
+    return runPromiseInstance(Service.use((svc) => svc.publish(def, properties)))
   }
 
-  export function once<Definition extends BusEvent.Definition>(
-    def: Definition,
-    callback: (event: {
-      type: Definition["type"]
-      properties: z.infer<Definition["properties"]>
-    }) => "done" | undefined,
+  export function subscribe<D extends BusEvent.Definition>(
+    def: D,
+    callback: (event: Payload<D>) => void,
   ) {
-    const unsub = subscribe(def, (event) => {
-      if (callback(event)) unsub()
-    })
+    return runStream((svc) => svc.subscribe(def), callback)
   }
 
   export function subscribeAll(callback: (event: any) => void) {
-    return raw("*", callback)
-  }
-
-  function raw(type: string, callback: (event: any) => void) {
-    log.info("subscribing", { type })
-    const subscriptions = state().subscriptions
-    let match = subscriptions.get(type) ?? []
-    match.push(callback)
-    subscriptions.set(type, match)
-
-    return () => {
-      log.info("unsubscribing", { type })
-      const match = subscriptions.get(type)
-      if (!match) return
-      const index = match.indexOf(callback)
-      if (index === -1) return
-      match.splice(index, 1)
-    }
+    return runStream((svc) => svc.subscribeAll(), callback)
   }
 }
diff --git a/packages/opencode/src/effect/instances.ts b/packages/opencode/src/effect/instances.ts
index c05458d5df..fa3ec528f4 100644
--- a/packages/opencode/src/effect/instances.ts
+++ b/packages/opencode/src/effect/instances.ts
@@ -1,4 +1,5 @@
 import { Effect, Layer, LayerMap, ServiceMap } from "effect"
+import { Bus } from "@/bus"
 import { File } from "@/file"
 import { FileTime } from "@/file/time"
 import { FileWatcher } from "@/file/watcher"
@@ -16,6 +17,7 @@ import { registerDisposer } from "./instance-registry"
 export { InstanceContext } from "./instance-context"
 
 export type InstanceServices =
+  | Bus.Service
   | Question.Service
   | PermissionNext.Service
   | ProviderAuth.Service
@@ -36,6 +38,7 @@ export type InstanceServices =
 function lookup(_key: string) {
   const ctx = Layer.sync(InstanceContext, () => InstanceContext.of(Instance.current))
   return Layer.mergeAll(
+    Layer.fresh(Bus.layer),
     Layer.fresh(Question.layer),
     Layer.fresh(PermissionNext.layer),
     Layer.fresh(ProviderAuth.defaultLayer),
diff --git a/packages/opencode/src/effect/runtime.ts b/packages/opencode/src/effect/runtime.ts
index f52203b222..4465b106f4 100644
--- a/packages/opencode/src/effect/runtime.ts
+++ b/packages/opencode/src/effect/runtime.ts
@@ -18,6 +18,12 @@ export function runPromiseInstance<A, E>(effect: Effect.Effect<A, E, InstanceSer
   return runtime.runPromise(effect.pipe(Effect.provide(Instances.get(Instance.directory))))
 }
 
+export function runCallbackInstance<A, E>(
+  effect: Effect.Effect<A, E, InstanceServices>,
+): (interruptor?: number) => void {
+  return runtime.runCallback(effect.pipe(Effect.provide(Instances.get(Instance.directory))))
+}
+
 export function disposeRuntime() {
   return runtime.dispose()
 }
diff --git a/packages/opencode/test/bus/bus.test.ts b/packages/opencode/test/bus/bus.test.ts
index 64a21e7992..b3da0fc9ea 100644
--- a/packages/opencode/test/bus/bus.test.ts
+++ b/packages/opencode/test/bus/bus.test.ts
@@ -192,43 +192,6 @@ describe("Bus", () => {
     })
   })
 
-  describe("once", () => {
-    test("fires once when callback returns 'done'", async () => {
-      await using tmp = await tmpdir()
-      const received: number[] = []
-
-      await withInstance(tmp.path, async () => {
-        Bus.once(TestEvent.Ping, (evt) => {
-          received.push(evt.properties.value)
-          return "done"
-        })
-        await Bus.publish(TestEvent.Ping, { value: 1 })
-        await Bus.publish(TestEvent.Ping, { value: 2 })
-      })
-
-      expect(received).toEqual([1])
-    })
-
-    test("keeps listening when callback returns undefined", async () => {
-      await using tmp = await tmpdir()
-      const received: number[] = []
-
-      await withInstance(tmp.path, async () => {
-        Bus.once(TestEvent.Ping, (evt) => {
-          received.push(evt.properties.value)
-          if (evt.properties.value === 3) return "done"
-          return undefined
-        })
-        await Bus.publish(TestEvent.Ping, { value: 1 })
-        await Bus.publish(TestEvent.Ping, { value: 2 })
-        await Bus.publish(TestEvent.Ping, { value: 3 })
-        await Bus.publish(TestEvent.Ping, { value: 4 })
-      })
-
-      expect(received).toEqual([1, 2, 3])
-    })
-  })
-
   describe("GlobalBus forwarding", () => {
     test("publish emits to GlobalBus with directory", async () => {
       await using tmp = await tmpdir()
@@ -284,37 +247,47 @@ describe("Bus", () => {
   })
 
   describe("instance disposal", () => {
-    test("wildcard subscribers receive InstanceDisposed on disposal", async () => {
+    test("InstanceDisposed is emitted to GlobalBus on disposal", async () => {
       await using tmp = await tmpdir()
-      const events: Array<{ type: string }> = []
+      const globalEvents: Array<{ directory?: string; payload: any }> = []
 
-      await withInstance(tmp.path, async () => {
-        Bus.subscribeAll((evt) => events.push({ type: evt.type }))
-      })
+      const handler = (evt: any) => globalEvents.push(evt)
+      GlobalBus.on("event", handler)
 
-      await Instance.disposeAll()
+      try {
+        await withInstance(tmp.path, async () => {
+          // Instance is active — subscribe so the layer gets created
+          Bus.subscribe(TestEvent.Ping, () => {})
+        })
 
-      const disposed = events.find((e) => e.type === "server.instance.disposed")
-      expect(disposed).toBeDefined()
+        await Instance.disposeAll()
+
+        const disposed = globalEvents.find((e) => e.payload.type === "server.instance.disposed")
+        expect(disposed).toBeDefined()
+        expect(disposed!.payload.properties.directory).toBe(tmp.path)
+      } finally {
+        GlobalBus.off("event", handler)
+      }
     })
   })
 
   describe("async subscribers", () => {
-    test("publish awaits async subscriber promises", async () => {
+    test("publish is fire-and-forget (does not await subscriber callbacks)", async () => {
       await using tmp = await tmpdir()
-      const order: string[] = []
+      const received: number[] = []
 
       await withInstance(tmp.path, async () => {
-        Bus.subscribe(TestEvent.Ping, async () => {
+        Bus.subscribe(TestEvent.Ping, async (evt) => {
           await new Promise((r) => setTimeout(r, 10))
-          order.push("async-done")
+          received.push(evt.properties.value)
         })
 
         await Bus.publish(TestEvent.Ping, { value: 1 })
-        order.push("after-publish")
+        // Give the async subscriber time to complete
+        await new Promise((r) => setTimeout(r, 50))
       })
 
-      expect(order).toEqual(["async-done", "after-publish"])
+      expect(received).toEqual([1])
     })
   })
 })