diff --git a/packages/opencode/test/bus/bus-effect.test.ts b/packages/opencode/test/bus/bus-effect.test.ts
index 377c541096..0dc58ecdae 100644
--- a/packages/opencode/test/bus/bus-effect.test.ts
+++ b/packages/opencode/test/bus/bus-effect.test.ts
@@ -1,5 +1,5 @@
 import { describe, expect } from "bun:test"
-import { Deferred, Effect, Layer, Schema, Stream } from "effect"
+import { Deferred, Effect, Fiber, Latch, Layer, Schema, Stream } from "effect"
 import { Bus } from "../../src/bus"
 import { BusEvent } from "../../src/bus/bus-event"
 import { CrossSpawnSpawner } from "@opencode-ai/core/cross-spawn-spawner"
@@ -9,6 +9,7 @@ import { testEffect } from "../lib/effect"
 const TestEvent = {
   Ping: BusEvent.define("test.effect.ping", Schema.Struct({ value: Schema.Number })),
   Pong: BusEvent.define("test.effect.pong", Schema.Struct({ message: Schema.String })),
+  Warmup: BusEvent.define("test.effect.warmup", Schema.Struct({})),
 }
 
 const node = CrossSpawnSpawner.defaultLayer
@@ -17,21 +18,44 @@ const live = Layer.mergeAll(Bus.layer, node)
 
 const it = testEffect(live)
 
+// Publishes warmup events until the latch opens, proving the forked subscriber
+// fiber has actually wired up its PubSub subscription.
+const awaitSubscriberReady = Effect.fn("test.awaitSubscriberReady")(function* (
+  ready: Latch.Latch,
+  warmup: Effect.Effect<void>,
+) {
+  const pump = yield* Effect.forkScoped(
+    Effect.gen(function* () {
+      while (true) {
+        yield* warmup
+        yield* Effect.sleep("5 millis")
+      }
+    }),
+  )
+  yield* ready.await.pipe(Effect.timeout("2 seconds"))
+  yield* Fiber.interrupt(pump)
+})
+
 describe("Bus (Effect-native)", () => {
   it.instance("publish + subscribe stream delivers events", () =>
     Effect.gen(function* () {
       const bus = yield* Bus.Service
       const received: number[] = []
       const done = yield* Deferred.make<void>()
+      const ready = yield* Latch.make()
 
       yield* Stream.runForEach(bus.subscribe(TestEvent.Ping), (evt) =>
-        Effect.sync(() => {
+        Effect.gen(function* () {
+          if (evt.properties.value < 0) {
+            yield* ready.open
+            return
+          }
           received.push(evt.properties.value)
           if (received.length === 2) Deferred.doneUnsafe(done, Effect.void)
         }),
       ).pipe(Effect.forkScoped)
 
-      yield* Effect.sleep("10 millis")
+      yield* awaitSubscriberReady(ready, bus.publish(TestEvent.Ping, { value: -1 }))
       yield* bus.publish(TestEvent.Ping, { value: 1 })
       yield* bus.publish(TestEvent.Ping, { value: 2 })
       yield* Deferred.await(done)
@@ -45,15 +69,20 @@ describe("Bus (Effect-native)", () => {
       const bus = yield* Bus.Service
       const pings: number[] = []
       const done = yield* Deferred.make<void>()
+      const ready = yield* Latch.make()
 
       yield* Stream.runForEach(bus.subscribe(TestEvent.Ping), (evt) =>
-        Effect.sync(() => {
+        Effect.gen(function* () {
+          if (evt.properties.value < 0) {
+            yield* ready.open
+            return
+          }
           pings.push(evt.properties.value)
           Deferred.doneUnsafe(done, Effect.void)
         }),
       ).pipe(Effect.forkScoped)
 
-      yield* Effect.sleep("10 millis")
+      yield* awaitSubscriberReady(ready, bus.publish(TestEvent.Ping, { value: -1 }))
       yield* bus.publish(TestEvent.Pong, { message: "ignored" })
       yield* bus.publish(TestEvent.Ping, { value: 42 })
       yield* Deferred.await(done)
@@ -67,15 +96,20 @@ describe("Bus (Effect-native)", () => {
       const bus = yield* Bus.Service
       const types: string[] = []
       const done = yield* Deferred.make<void>()
+      const ready = yield* Latch.make()
 
       yield* Stream.runForEach(bus.subscribeAll(), (evt) =>
-        Effect.sync(() => {
+        Effect.gen(function* () {
+          if (evt.type === TestEvent.Warmup.type) {
+            yield* ready.open
+            return
+          }
           types.push(evt.type)
           if (types.length === 2) Deferred.doneUnsafe(done, Effect.void)
         }),
       ).pipe(Effect.forkScoped)
 
-      yield* Effect.sleep("10 millis")
+      yield* awaitSubscriberReady(ready, bus.publish(TestEvent.Warmup, {}))
       yield* bus.publish(TestEvent.Ping, { value: 1 })
       yield* bus.publish(TestEvent.Pong, { message: "hi" })
       yield* Deferred.await(done)
@@ -92,22 +126,33 @@ describe("Bus (Effect-native)", () => {
       const b: number[] = []
       const doneA = yield* Deferred.make<void>()
       const doneB = yield* Deferred.make<void>()
+      const readyA = yield* Latch.make()
+      const readyB = yield* Latch.make()
 
       yield* Stream.runForEach(bus.subscribe(TestEvent.Ping), (evt) =>
-        Effect.sync(() => {
+        Effect.gen(function* () {
+          if (evt.properties.value < 0) {
+            yield* readyA.open
+            return
+          }
           a.push(evt.properties.value)
           Deferred.doneUnsafe(doneA, Effect.void)
         }),
       ).pipe(Effect.forkScoped)
 
       yield* Stream.runForEach(bus.subscribe(TestEvent.Ping), (evt) =>
-        Effect.sync(() => {
+        Effect.gen(function* () {
+          if (evt.properties.value < 0) {
+            yield* readyB.open
+            return
+          }
           b.push(evt.properties.value)
           Deferred.doneUnsafe(doneB, Effect.void)
         }),
       ).pipe(Effect.forkScoped)
 
-      yield* Effect.sleep("10 millis")
+      yield* awaitSubscriberReady(readyA, bus.publish(TestEvent.Ping, { value: -1 }))
+      yield* awaitSubscriberReady(readyB, bus.publish(TestEvent.Ping, { value: -1 }))
       yield* bus.publish(TestEvent.Ping, { value: 99 })
       yield* Deferred.await(doneA)
       yield* Deferred.await(doneB)
@@ -123,20 +168,25 @@ describe("Bus (Effect-native)", () => {
       const types: string[] = []
       const seen = yield* Deferred.make<void>()
       const disposed = yield* Deferred.make<void>()
+      const ready = yield* Latch.make()
 
       // Set up subscriber inside the instance
       yield* Effect.gen(function* () {
         const bus = yield* Bus.Service
 
         yield* Stream.runForEach(bus.subscribeAll(), (evt) =>
-          Effect.sync(() => {
+          Effect.gen(function* () {
+            if (evt.type === TestEvent.Warmup.type) {
+              yield* ready.open
+              return
+            }
             types.push(evt.type)
             if (evt.type === TestEvent.Ping.type) Deferred.doneUnsafe(seen, Effect.void)
             if (evt.type === Bus.InstanceDisposed.type) Deferred.doneUnsafe(disposed, Effect.void)
           }),
         ).pipe(Effect.forkScoped)
 
-        yield* Effect.sleep("10 millis")
+        yield* awaitSubscriberReady(ready, bus.publish(TestEvent.Warmup, {}))
         yield* bus.publish(TestEvent.Ping, { value: 1 })
         yield* Deferred.await(seen)
       }).pipe(provideInstance(dir))