fix(bus): acquire PubSub subscription eagerly to close /event race (#27959)

packages/opencode/src/bus/index.ts

@@ -37,8 +37,16 @@ export interface Interface {
     properties: BusProperties<D>,
     options?: { id?: string },
   ) => Effect.Effect<void>
-  readonly subscribe: <D extends BusEvent.Definition>(def: D) => Stream.Stream<Payload<D>>
-  readonly subscribeAll: () => Stream.Stream<Payload>
+  // subscribe / subscribeAll are eager: the underlying PubSub subscription is
+  // acquired in the caller's Scope at `yield*` time. Any publish after the
+  // yield is delivered, even if stream consumption starts later. The previous
+  // Stream-returning shape acquired the subscription lazily on first pull,
+  // opening a race window during which publishes were lost — see
+  // test/bus/bus-effect.test.ts RACE tests.
+  readonly subscribe: <D extends BusEvent.Definition>(
+    def: D,
+  ) => Effect.Effect<Stream.Stream<Payload<D>>, never, Scope.Scope>
+  readonly subscribeAll: () => Effect.Effect<Stream.Stream<Payload>, never, Scope.Scope>
   readonly subscribeCallback: <D extends BusEvent.Definition>(
     def: D,
     callback: (event: Payload<D>) => unknown,
@@ -109,26 +117,26 @@ export const layer = Layer.effect(
       })
     }
 
-    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 s = yield* InstanceState.get(state)
-          const ps = yield* getOrCreate(s, def)
-          return Stream.fromPubSub(ps)
-        }),
-      ).pipe(Stream.ensuring(Effect.sync(() => log.info("unsubscribing", { type: def.type }))))
-    }
+    const subscribe = <D extends BusEvent.Definition>(
+      def: D,
+    ): Effect.Effect<Stream.Stream<Payload<D>>, never, Scope.Scope> =>
+      Effect.gen(function* () {
+        log.info("subscribing", { type: def.type })
+        const s = yield* InstanceState.get(state)
+        const ps = yield* getOrCreate(s, def)
+        const subscription = yield* PubSub.subscribe(ps)
+        yield* Effect.addFinalizer(() => Effect.sync(() => log.info("unsubscribing", { type: def.type })))
+        return Stream.fromSubscription(subscription)
+      })
 
-    function subscribeAll(): Stream.Stream<Payload> {
-      log.info("subscribing", { type: "*" })
-      return Stream.unwrap(
-        Effect.gen(function* () {
-          const s = yield* InstanceState.get(state)
-          return Stream.fromPubSub(s.wildcard)
-        }),
-      ).pipe(Stream.ensuring(Effect.sync(() => log.info("unsubscribing", { type: "*" }))))
-    }
+    const subscribeAll = (): Effect.Effect<Stream.Stream<Payload>, never, Scope.Scope> =>
+      Effect.gen(function* () {
+        log.info("subscribing", { type: "*" })
+        const s = yield* InstanceState.get(state)
+        const subscription = yield* PubSub.subscribe(s.wildcard)
+        yield* Effect.addFinalizer(() => Effect.sync(() => log.info("unsubscribing", { type: "*" })))
+        return Stream.fromSubscription(subscription)
+      })
 
     function on<T>(pubsub: PubSub.PubSub<T>, type: string, callback: (event: T) => unknown) {
       return Effect.gen(function* () {

packages/opencode/src/plugin/index.ts

@@ -243,7 +243,7 @@ export const layer = Layer.effect(
         }
 
         // Subscribe to bus events, fiber interrupted when scope closes
-        yield* bus.subscribeAll().pipe(
+        yield* (yield* bus.subscribeAll()).pipe(
           Stream.runForEach((input) =>
             Effect.sync(() => {
               for (const hook of hooks) {

packages/opencode/src/project/project.ts

@@ -425,7 +425,7 @@ export const layer: Layer.Layer<
 
     const initState = yield* InstanceState.make(
       Effect.fn("Project.initState")(function* (ctx) {
-        yield* bus.subscribe(Command.Event.Executed).pipe(
+        yield* (yield* bus.subscribe(Command.Event.Executed)).pipe(
           Stream.runForEach((payload) =>
             payload.properties.name === Command.Default.INIT ? setInitialized(ctx.project.id) : Effect.void,
           ),

packages/opencode/src/project/vcs.ts

@@ -298,7 +298,7 @@ export const layer: Layer.Layer<Service, never, Git.Service | Bus.Service> = Lay
         const value = { current, root }
         log.info("initialized", { branch: value.current, default_branch: value.root?.name })
 
-        yield* bus.subscribe(FileWatcher.Event.Updated).pipe(
+        yield* (yield* bus.subscribe(FileWatcher.Event.Updated)).pipe(
           Stream.filter((evt) => evt.properties.file.endsWith("HEAD")),
           Stream.runForEach((_evt) =>
             Effect.gen(function* () {

packages/opencode/src/server/routes/instance/httpapi/handlers/event.ts

@@ -20,10 +20,11 @@ function eventData(data: unknown): Sse.Event {
 
 function eventResponse(bus: Bus.Interface) {
   return Effect.gen(function* () {
-    const context = yield* Effect.context()
-
-    const events = bus.subscribeAll().pipe(
-      Stream.provideContext(context),
+    // Subscribe eagerly: the bus subscription is acquired in the request scope
+    // at this yield, so any publish from now on is queued for the body-pump
+    // fiber to drain — closing the race where Stream.concat(server.connected,
+    // lazy-subscribe) used to drop publishes in the prefix-consume window.
+    const events = (yield* bus.subscribeAll()).pipe(
       Stream.takeUntil((event) => event.type === Bus.InstanceDisposed.type),
     )
     const heartbeat = Stream.tick("10 seconds").pipe(

packages/opencode/src/share/share-next.ts

@@ -168,16 +168,20 @@ export const layer = Layer.effect(
           fn: (evt: { properties: any }) => Effect.Effect<void, unknown>,
         ) =>
           bus.subscribe(def as never).pipe(
-            Stream.runForEach((evt) =>
-              fn(evt).pipe(
-                Effect.catchCause((cause) =>
-                  Effect.sync(() => {
-                    log.error("share subscriber failed", { type: def.type, cause })
-                  }),
+            Effect.flatMap((stream) =>
+              stream.pipe(
+                Stream.runForEach((evt) =>
+                  fn(evt).pipe(
+                    Effect.catchCause((cause) =>
+                      Effect.sync(() => {
+                        log.error("share subscriber failed", { type: def.type, cause })
+                      }),
+                    ),
+                  ),
                 ),
+                Effect.forkScoped,
               ),
             ),
-            Effect.forkScoped,
           )
 
         yield* watch(Session.Event.Updated, (evt) =>

packages/opencode/test/bus/bus-effect.test.ts

@@ -44,7 +44,7 @@ describe("Bus (Effect-native)", () => {
       const done = yield* Deferred.make<void>()
       const ready = yield* Latch.make()
 
-      yield* Stream.runForEach(bus.subscribe(TestEvent.Ping), (evt) =>
+      yield* Stream.runForEach(yield* bus.subscribe(TestEvent.Ping), (evt) =>
         Effect.gen(function* () {
           if (evt.properties.value < 0) {
             yield* ready.open
@@ -71,7 +71,7 @@ describe("Bus (Effect-native)", () => {
       const done = yield* Deferred.make<void>()
       const ready = yield* Latch.make()
 
-      yield* Stream.runForEach(bus.subscribe(TestEvent.Ping), (evt) =>
+      yield* Stream.runForEach(yield* bus.subscribe(TestEvent.Ping), (evt) =>
         Effect.gen(function* () {
           if (evt.properties.value < 0) {
             yield* ready.open
@@ -98,7 +98,7 @@ describe("Bus (Effect-native)", () => {
       const done = yield* Deferred.make<void>()
       const ready = yield* Latch.make()
 
-      yield* Stream.runForEach(bus.subscribeAll(), (evt) =>
+      yield* Stream.runForEach(yield* bus.subscribeAll(), (evt) =>
         Effect.gen(function* () {
           if (evt.type === TestEvent.Warmup.type) {
             yield* ready.open
@@ -129,7 +129,7 @@ describe("Bus (Effect-native)", () => {
       const readyA = yield* Latch.make()
       const readyB = yield* Latch.make()
 
-      yield* Stream.runForEach(bus.subscribe(TestEvent.Ping), (evt) =>
+      yield* Stream.runForEach(yield* bus.subscribe(TestEvent.Ping), (evt) =>
         Effect.gen(function* () {
           if (evt.properties.value < 0) {
             yield* readyA.open
@@ -140,7 +140,7 @@ describe("Bus (Effect-native)", () => {
         }),
       ).pipe(Effect.forkScoped)
 
-      yield* Stream.runForEach(bus.subscribe(TestEvent.Ping), (evt) =>
+      yield* Stream.runForEach(yield* bus.subscribe(TestEvent.Ping), (evt) =>
         Effect.gen(function* () {
           if (evt.properties.value < 0) {
             yield* readyB.open
@@ -162,6 +162,92 @@ describe("Bus (Effect-native)", () => {
     }),
   )
 
+  // RACE 1: eager subscription means publishing immediately after yield*
+  // bus.subscribe is delivered. Regression for the old lazy `Stream.unwrap`
+  // shape where PubSub.subscribe ran on first pull and missed any publish
+  // in the hand-off window.
+  it.instance("eager subscribe: publish after yield* is delivered without consumer-activation race", () =>
+    Effect.gen(function* () {
+      const bus = yield* Bus.Service
+      const stream = yield* bus.subscribe(TestEvent.Ping)
+
+      // Hand-off window: subscription is alive (we yielded). Publish goes
+      // straight into the subscription queue, even with no consumer running.
+      yield* bus.publish(TestEvent.Ping, { value: 99 })
+
+      const collected = yield* stream.pipe(
+        Stream.take(1),
+        Stream.runCollect,
+        Effect.timeout("400 millis"),
+        Effect.option,
+      )
+
+      expect(collected._tag).toBe("Some")
+      if (collected._tag === "Some") {
+        const arr = Array.from(collected.value)
+        expect(arr[0].properties.value).toBe(99)
+      }
+    }),
+  )
+
+  // RACE 2: same property for subscribeAll.
+  it.instance("eager subscribeAll: publish after yield* is delivered", () =>
+    Effect.gen(function* () {
+      const bus = yield* Bus.Service
+      const stream = yield* bus.subscribeAll()
+
+      yield* bus.publish(TestEvent.Ping, { value: 42 })
+
+      const collected = yield* stream.pipe(
+        Stream.take(1),
+        Stream.runCollect,
+        Effect.timeout("400 millis"),
+        Effect.option,
+      )
+
+      expect(collected._tag).toBe("Some")
+      if (collected._tag === "Some") {
+        const arr = Array.from(collected.value)
+        expect(arr[0].type).toBe(TestEvent.Ping.type)
+      }
+    }),
+  )
+
+  // RACE 3: the /event-handler shape exactly. With eager subscription, the
+  // bus subscription is alive before Stream.concat ever starts. Publishes
+  // during the prefix consumption window are queued and delivered.
+  it.instance("eager subscribe: Stream.concat(initial, subscribe) delivers publish during prefix", () =>
+    Effect.gen(function* () {
+      const bus = yield* Bus.Service
+      const sawInitial = yield* Deferred.make<void>()
+      const sawPublish = yield* Deferred.make<number>()
+
+      type Frame = { marker?: "initial"; value?: number }
+      const subscriptionStream = yield* bus.subscribe(TestEvent.Ping)
+      const handlerStream: Stream.Stream<Frame> = Stream.make({ marker: "initial" } as Frame).pipe(
+        Stream.concat(subscriptionStream.pipe(Stream.map((evt): Frame => ({ value: evt.properties.value })))),
+      )
+
+      yield* Stream.runForEach(handlerStream, (frame) =>
+        Effect.gen(function* () {
+          if (frame.marker === "initial") {
+            Deferred.doneUnsafe(sawInitial, Effect.void)
+            return
+          }
+          if (frame.value !== undefined) Deferred.doneUnsafe(sawPublish, Effect.succeed(frame.value))
+        }),
+      ).pipe(Effect.forkScoped)
+
+      yield* Deferred.await(sawInitial).pipe(Effect.timeout("1 second"))
+
+      yield* bus.publish(TestEvent.Ping, { value: 7 })
+
+      const got = yield* Deferred.await(sawPublish).pipe(Effect.timeout("1 second"), Effect.option)
+      expect(got._tag).toBe("Some")
+      if (got._tag === "Some") expect(got.value).toBe(7)
+    }),
+  )
+
   it.live("subscribeAll stream sees InstanceDisposed on disposal", () =>
     Effect.gen(function* () {
       const dir = yield* tmpdirScoped()
@@ -174,7 +260,7 @@ describe("Bus (Effect-native)", () => {
       yield* Effect.gen(function* () {
         const bus = yield* Bus.Service
 
-        yield* Stream.runForEach(bus.subscribeAll(), (evt) =>
+        yield* Stream.runForEach(yield* bus.subscribeAll(), (evt) =>
           Effect.gen(function* () {
             if (evt.type === TestEvent.Warmup.type) {
               yield* ready.open

packages/opencode/test/server/httpapi-event-diagnostics.test.ts

@@ -0,0 +1,453 @@
+// Diagnostic suite for /event SSE delivery.
+//
+// Each test isolates ONE variable in the publisher chain while keeping the
+// subscriber path constant (raw `app().request` reading the SSE body — no SDK
+// consumer involvement). The pass/fail pattern across tests tells us where the
+// bug lives:
+//
+//   D1 (baseline): publish via Bus.Service.use via AppRuntime — mirror of the
+//        existing httpapi-event.test.ts test 3. Confirms /event SSE delivery
+//        works for a SOME publish path.
+//
+//   D2: publish N times in quick succession via Bus.Service.use. If the bus
+//        subscription is acquired correctly there should be no message loss.
+//
+//   D3: publish via SyncEvent.use.run via AppRuntime — exercises the same path
+//        the HTTP handlers use (Session.updatePart → sync.run → bus.publish)
+//        without the HTTP roundtrip. Tells us whether the sync path itself can
+//        deliver in-process.
+//
+//   D4: publish via SyncEvent.use.run from a fresh `Effect.provide` scope
+//        (mimicking what happens if a handler's layer was scoped per-request).
+//
+//   D5: in-process Bus.Service callback subscriber AND raw /event SSE subscriber
+//        receive the same publish. If both receive: no bug. If only the
+//        callback receives: the /event handler has an acquisition race.
+import { afterEach, describe, expect, test } from "bun:test"
+import { Bus } from "../../src/bus"
+import { AppRuntime } from "../../src/effect/app-runtime"
+import { InstanceRef } from "../../src/effect/instance-ref"
+import { Server } from "../../src/server/server"
+import { EventPaths } from "../../src/server/routes/instance/httpapi/groups/event"
+import { Event as ServerEvent } from "../../src/server/event"
+import { SyncEvent } from "../../src/sync"
+import { MessageV2 } from "../../src/session/message-v2"
+import { MessageID, PartID, SessionID } from "../../src/session/schema"
+import * as Log from "@opencode-ai/core/util/log"
+import { Effect, Schema } from "effect"
+import { resetDatabase } from "../fixture/db"
+import { disposeAllInstances, reloadTestInstance, tmpdir } from "../fixture/fixture"
+
+void Log.init({ print: false })
+
+function app() {
+  return Server.Default().app
+}
+
+const EventData = Schema.Struct({
+  id: Schema.optional(Schema.String),
+  type: Schema.String,
+  properties: Schema.Record(Schema.String, Schema.Any),
+})
+
+type SseEvent = Schema.Schema.Type<typeof EventData>
+
+async function readChunk(reader: ReadableStreamDefaultReader<Uint8Array>, timeoutMs = 3_000) {
+  let timeout: ReturnType<typeof setTimeout> | undefined
+  try {
+    return await Promise.race([
+      reader.read(),
+      new Promise<never>((_, reject) => {
+        timeout = setTimeout(() => reject(new Error(`timed out after ${timeoutMs}ms`)), timeoutMs)
+      }),
+    ])
+  } finally {
+    if (timeout) clearTimeout(timeout)
+  }
+}
+
+const textDecoder = new TextDecoder()
+
+function decodeFrame(value: Uint8Array): SseEvent[] {
+  // SSE frames are separated by blank lines and each starts with "data: ".
+  // For our happy-path tests one chunk == one frame, but be defensive.
+  const text = textDecoder.decode(value)
+  return text
+    .split(/\n\n+/)
+    .map((part) => part.trim())
+    .filter((part) => part.length > 0)
+    .map((part) => {
+      const payload = part.replace(/^data: /, "")
+      return Schema.decodeUnknownSync(EventData)(JSON.parse(payload))
+    })
+}
+
+async function readNextEvent(reader: ReadableStreamDefaultReader<Uint8Array>, timeoutMs = 3_000): Promise<SseEvent> {
+  const result = await readChunk(reader, timeoutMs)
+  if (result.done || !result.value) throw new Error("event stream closed")
+  const frames = decodeFrame(result.value)
+  if (frames.length === 0) throw new Error("empty SSE frame")
+  return frames[0]
+}
+
+async function collectUntil(
+  reader: ReadableStreamDefaultReader<Uint8Array>,
+  predicate: (event: SseEvent) => boolean,
+  timeoutMs = 3_000,
+): Promise<SseEvent[]> {
+  const events: SseEvent[] = []
+  const deadline = Date.now() + timeoutMs
+  while (Date.now() < deadline) {
+    const remaining = deadline - Date.now()
+    const result = await readChunk(reader, remaining).catch((cause) => {
+      throw new Error(`collectUntil timed out after ${events.length} events: ${cause}`)
+    })
+    if (result.done || !result.value) throw new Error("event stream closed mid-collect")
+    for (const event of decodeFrame(result.value)) {
+      events.push(event)
+      if (predicate(event)) return events
+    }
+  }
+  throw new Error(`collectUntil deadline exceeded; collected ${events.length}: ${JSON.stringify(events)}`)
+}
+
+afterEach(async () => {
+  await disposeAllInstances()
+  await resetDatabase()
+})
+
+describe("/event SSE delivery diagnostics", () => {
+  // Sanity: baseline same as httpapi-event.test.ts test 3 (already known to pass)
+  // but explicit about timing — publish happens with NO wait after reading
+  // server.connected. If this fails we have a deeper problem than just sync.
+  test("D1: delivers a single bus event published right after server.connected", async () => {
+    await using tmp = await tmpdir({ git: true, config: { formatter: false, lsp: false } })
+    const response = await app().request(EventPaths.event, { headers: { "x-opencode-directory": tmp.path } })
+    if (!response.body) throw new Error("missing response body")
+    const reader = response.body.getReader()
+    try {
+      const first = await readNextEvent(reader)
+      expect(first.type).toBe("server.connected")
+
+      const ctx = await reloadTestInstance({ directory: tmp.path })
+      // NO wait — publish immediately
+      await AppRuntime.runPromise(
+        Bus.Service.use((svc) => svc.publish(ServerEvent.Connected, {})).pipe(Effect.provideService(InstanceRef, ctx)),
+      )
+
+      const next = await readNextEvent(reader)
+      expect(next.type).toBe("server.connected") // ServerEvent.Connected.type === "server.connected"
+    } finally {
+      await reader.cancel()
+    }
+  })
+
+  // If D1 passes but D2 fails, we have a queue-drain or partial-loss issue.
+  test("D2: delivers all N bus events published in rapid succession", async () => {
+    await using tmp = await tmpdir({ git: true, config: { formatter: false, lsp: false } })
+    const response = await app().request(EventPaths.event, { headers: { "x-opencode-directory": tmp.path } })
+    if (!response.body) throw new Error("missing response body")
+    const reader = response.body.getReader()
+    try {
+      const first = await readNextEvent(reader)
+      expect(first.type).toBe("server.connected")
+
+      const ctx = await reloadTestInstance({ directory: tmp.path })
+      const N = 5
+      for (let i = 0; i < N; i++) {
+        await AppRuntime.runPromise(
+          Bus.Service.use((svc) => svc.publish(ServerEvent.Connected, {})).pipe(
+            Effect.provideService(InstanceRef, ctx),
+          ),
+        )
+      }
+
+      const received: SseEvent[] = []
+      for (let i = 0; i < N; i++) {
+        received.push(await readNextEvent(reader))
+      }
+      expect(received).toHaveLength(N)
+      for (const event of received) expect(event.type).toBe("server.connected")
+    } finally {
+      await reader.cancel()
+    }
+  })
+
+  // The critical test. If D1 passes but this fails, the bus-identity fix is
+  // incomplete OR the sync.run publish path doesn't reach the same bus
+  // /event subscribes to, even within the same AppRuntime.
+  test("D3: delivers a SyncEvent published via SyncEvent.use.run after server.connected", async () => {
+    await using tmp = await tmpdir({ git: true, config: { formatter: false, lsp: false } })
+    const response = await app().request(EventPaths.event, { headers: { "x-opencode-directory": tmp.path } })
+    if (!response.body) throw new Error("missing response body")
+    const reader = response.body.getReader()
+    try {
+      const first = await readNextEvent(reader)
+      expect(first.type).toBe("server.connected")
+
+      const ctx = await reloadTestInstance({ directory: tmp.path })
+      const sessionID = SessionID.make(`ses_${Date.now().toString(36)}${Math.random().toString(36).slice(2, 8)}`)
+      const messageID = MessageID.ascending()
+      const partID = PartID.ascending()
+      const part: MessageV2.Part = {
+        id: partID,
+        sessionID,
+        messageID,
+        type: "text",
+        text: "diag",
+      }
+
+      await AppRuntime.runPromise(
+        SyncEvent.use
+          .run(MessageV2.Event.PartUpdated, {
+            sessionID,
+            part: structuredClone(part) as MessageV2.Part,
+            time: Date.now(),
+          })
+          .pipe(Effect.provideService(InstanceRef, ctx)),
+      )
+
+      const collected = await collectUntil(
+        reader,
+        (event) => event.type === MessageV2.Event.PartUpdated.type,
+        4_000,
+      )
+      const updated = collected.find((event) => event.type === MessageV2.Event.PartUpdated.type)
+      expect(updated).toBeDefined()
+      expect((updated as any).properties.part.id).toBe(partID)
+    } finally {
+      await reader.cancel()
+    }
+  })
+
+  // If D3 passes but D5 (the SDK E2E in httpapi-sdk.test.ts) fails, then the
+  // bug is specifically in the cross-request / cross-fiber HTTP path, not in
+  // the publish itself. If D3 also fails, the publish chain is broken.
+  //
+  // D4: ensure the publish reaches an in-process Bus subscriber too. Confirms
+  // pub/sub identity end-to-end without involving /event SSE.
+  test("D4: SyncEvent.use.run publish reaches an in-process Bus.Service.use callback", async () => {
+    await using tmp = await tmpdir({ git: true, config: { formatter: false, lsp: false } })
+    const ctx = await reloadTestInstance({ directory: tmp.path })
+
+    let resolveReceived: (event: { id: string; type: string; properties: unknown }) => void
+    const received = new Promise<{ id: string; type: string; properties: unknown }>(
+      (resolve) => (resolveReceived = resolve as typeof resolveReceived),
+    )
+
+    const dispose = await AppRuntime.runPromise(
+      Bus.Service.use((svc) =>
+        svc.subscribeAllCallback((event) => {
+          if (event.type === MessageV2.Event.PartUpdated.type) resolveReceived(event)
+        }),
+      ).pipe(Effect.provideService(InstanceRef, ctx)),
+    )
+
+    try {
+      const sessionID = SessionID.make(`ses_${Date.now().toString(36)}${Math.random().toString(36).slice(2, 8)}`)
+      const messageID = MessageID.ascending()
+      const partID = PartID.ascending()
+      const part: MessageV2.Part = { id: partID, sessionID, messageID, type: "text", text: "diag-d4" }
+
+      await AppRuntime.runPromise(
+        SyncEvent.use
+          .run(MessageV2.Event.PartUpdated, {
+            sessionID,
+            part: structuredClone(part) as MessageV2.Part,
+            time: Date.now(),
+          })
+          .pipe(Effect.provideService(InstanceRef, ctx)),
+      )
+
+      const event = await Promise.race([
+        received,
+        new Promise<never>((_, reject) => setTimeout(() => reject(new Error("D4 timed out")), 3_000)),
+      ])
+      expect(event.type).toBe(MessageV2.Event.PartUpdated.type)
+      expect((event.properties as any).part.id).toBe(partID)
+    } finally {
+      dispose()
+    }
+  })
+
+  // D5: BOTH subscribers attached simultaneously. Trigger ONE publish via
+  // SyncEvent.use.run. Both subscribers should receive it. If only one does
+  // we know exactly which side of the chain is failing.
+  test("D5: same SyncEvent.use.run publish reaches BOTH /event SSE and in-process callback", async () => {
+    await using tmp = await tmpdir({ git: true, config: { formatter: false, lsp: false } })
+    const ctx = await reloadTestInstance({ directory: tmp.path })
+
+    // In-process callback subscriber
+    let resolveCallback: (event: { type: string; properties: unknown }) => void
+    const callbackReceived = new Promise<{ type: string; properties: unknown }>(
+      (resolve) => (resolveCallback = resolve as typeof resolveCallback),
+    )
+    const dispose = await AppRuntime.runPromise(
+      Bus.Service.use((svc) =>
+        svc.subscribeAllCallback((event) => {
+          if (event.type === MessageV2.Event.PartUpdated.type) resolveCallback(event)
+        }),
+      ).pipe(Effect.provideService(InstanceRef, ctx)),
+    )
+
+    // SSE subscriber via raw HTTP
+    const response = await app().request(EventPaths.event, { headers: { "x-opencode-directory": tmp.path } })
+    if (!response.body) throw new Error("missing response body")
+    const reader = response.body.getReader()
+
+    try {
+      const first = await readNextEvent(reader)
+      expect(first.type).toBe("server.connected")
+
+      const sessionID = SessionID.make(`ses_${Date.now().toString(36)}${Math.random().toString(36).slice(2, 8)}`)
+      const messageID = MessageID.ascending()
+      const partID = PartID.ascending()
+      const part: MessageV2.Part = { id: partID, sessionID, messageID, type: "text", text: "diag-d5" }
+
+      await AppRuntime.runPromise(
+        SyncEvent.use
+          .run(MessageV2.Event.PartUpdated, {
+            sessionID,
+            part: structuredClone(part) as MessageV2.Part,
+            time: Date.now(),
+          })
+          .pipe(Effect.provideService(InstanceRef, ctx)),
+      )
+
+      const sseCollected = await collectUntil(
+        reader,
+        (event) => event.type === MessageV2.Event.PartUpdated.type,
+        4_000,
+      ).catch((err) => err as Error)
+      const callbackResult = await Promise.race([
+        callbackReceived,
+        new Promise<"timeout">((resolve) => setTimeout(() => resolve("timeout"), 1_000)),
+      ])
+
+      const sseSaw =
+        Array.isArray(sseCollected) &&
+        sseCollected.some((event) => event.type === MessageV2.Event.PartUpdated.type)
+      const callbackSaw = callbackResult !== "timeout"
+
+      // Both should see it. The reason we use a single assert with the boolean
+      // pair is so the test failure message tells us exactly which side broke.
+      expect({ sseSaw, callbackSaw }).toEqual({ sseSaw: true, callbackSaw: true })
+    } finally {
+      await reader.cancel()
+      dispose()
+    }
+  })
+
+  // D7: like D5 but the "second subscriber" is a NO-OP AppRuntime.runPromise
+  // call (no PubSub.subscribe). If D7 passes, the specific subscribeAllCallback
+  // is what breaks SSE — not arbitrary AppRuntime usage. If D7 fails, anything
+  // running through AppRuntime concurrently with /event SSE breaks delivery.
+  test("D7: SSE receives sync.run publish even with concurrent no-op AppRuntime activity", async () => {
+    await using tmp = await tmpdir({ git: true, config: { formatter: false, lsp: false } })
+    const ctx = await reloadTestInstance({ directory: tmp.path })
+
+    // No-op: just touches the runtime, no bus interaction
+    await AppRuntime.runPromise(Effect.void)
+
+    const response = await app().request(EventPaths.event, { headers: { "x-opencode-directory": tmp.path } })
+    if (!response.body) throw new Error("missing response body")
+    const reader = response.body.getReader()
+    try {
+      const first = await readNextEvent(reader)
+      expect(first.type).toBe("server.connected")
+
+      const sessionID = SessionID.make(`ses_${Date.now().toString(36)}${Math.random().toString(36).slice(2, 8)}`)
+      const messageID = MessageID.ascending()
+      const partID = PartID.ascending()
+      const part: MessageV2.Part = { id: partID, sessionID, messageID, type: "text", text: "diag-d7" }
+
+      await AppRuntime.runPromise(
+        SyncEvent.use
+          .run(MessageV2.Event.PartUpdated, {
+            sessionID,
+            part: structuredClone(part) as MessageV2.Part,
+            time: Date.now(),
+          })
+          .pipe(Effect.provideService(InstanceRef, ctx)),
+      )
+
+      const collected = await collectUntil(
+        reader,
+        (event) => event.type === MessageV2.Event.PartUpdated.type,
+        4_000,
+      )
+      const updated = collected.find((event) => event.type === MessageV2.Event.PartUpdated.type)
+      expect(updated).toBeDefined()
+    } finally {
+      await reader.cancel()
+    }
+  })
+
+  // D6: same as D5 but the callback subscriber is attached AFTER /event SSE
+  // subscription is established. If D5 fails and D6 passes, the order of
+  // subscriber setup is the determining factor.
+  test("D6: /event SSE receives sync.run publish when callback is attached AFTER /event opens", async () => {
+    await using tmp = await tmpdir({ git: true, config: { formatter: false, lsp: false } })
+    const ctx = await reloadTestInstance({ directory: tmp.path })
+
+    // Open SSE FIRST
+    const response = await app().request(EventPaths.event, { headers: { "x-opencode-directory": tmp.path } })
+    if (!response.body) throw new Error("missing response body")
+    const reader = response.body.getReader()
+
+    try {
+      const first = await readNextEvent(reader)
+      expect(first.type).toBe("server.connected")
+
+      // THEN attach callback subscriber
+      let resolveCallback: (event: { type: string; properties: unknown }) => void
+      const callbackReceived = new Promise<{ type: string; properties: unknown }>(
+        (resolve) => (resolveCallback = resolve as typeof resolveCallback),
+      )
+      const dispose = await AppRuntime.runPromise(
+        Bus.Service.use((svc) =>
+          svc.subscribeAllCallback((event) => {
+            if (event.type === MessageV2.Event.PartUpdated.type) resolveCallback(event)
+          }),
+        ).pipe(Effect.provideService(InstanceRef, ctx)),
+      )
+
+      try {
+        const sessionID = SessionID.make(`ses_${Date.now().toString(36)}${Math.random().toString(36).slice(2, 8)}`)
+        const messageID = MessageID.ascending()
+        const partID = PartID.ascending()
+        const part: MessageV2.Part = { id: partID, sessionID, messageID, type: "text", text: "diag-d6" }
+
+        await AppRuntime.runPromise(
+          SyncEvent.use
+            .run(MessageV2.Event.PartUpdated, {
+              sessionID,
+              part: structuredClone(part) as MessageV2.Part,
+              time: Date.now(),
+            })
+            .pipe(Effect.provideService(InstanceRef, ctx)),
+        )
+
+        const sseCollected = await collectUntil(
+          reader,
+          (event) => event.type === MessageV2.Event.PartUpdated.type,
+          4_000,
+        ).catch((err) => err as Error)
+        const callbackResult = await Promise.race([
+          callbackReceived,
+          new Promise<"timeout">((resolve) => setTimeout(() => resolve("timeout"), 1_000)),
+        ])
+
+        const sseSaw =
+          Array.isArray(sseCollected) &&
+          sseCollected.some((event) => event.type === MessageV2.Event.PartUpdated.type)
+        const callbackSaw = callbackResult !== "timeout"
+        expect({ sseSaw, callbackSaw }).toEqual({ sseSaw: true, callbackSaw: true })
+      } finally {
+        dispose()
+      }
+    } finally {
+      await reader.cancel()
+    }
+  })
+})

packages/opencode/test/server/httpapi-sdk.test.ts

@@ -1,5 +1,5 @@
 import { afterEach, describe, expect } from "bun:test"
-import { ConfigProvider, Effect, Layer } from "effect"
+import { ConfigProvider, Deferred, Effect, Layer } from "effect"
 import type * as Scope from "effect/Scope"
 import { HttpRouter } from "effect/unstable/http"
 import { ChildProcessSpawner } from "effect/unstable/process"
@@ -22,7 +22,7 @@ import { TestLLMServer } from "../lib/llm-server"
 import path from "path"
 import { resetDatabase } from "../fixture/db"
 import { disposeAllInstances, TestInstance, tmpdirScoped } from "../fixture/fixture"
-import { testEffect } from "../lib/effect"
+import { awaitWithTimeout, testEffect } from "../lib/effect"
 
 const noopBootstrap = Layer.succeed(InstanceBootstrap.Service, InstanceBootstrap.Service.of({ run: Effect.void }))
 const it = testEffect(
@@ -671,6 +671,70 @@ describe("HttpApi SDK", () => {
     ),
   )
 
+  // Regression: SyncEvent must publish on the same ProjectBus the /event handler
+// subscribes to, AND the /event stream must forward handler ALS/context into the
+// body-pump fiber. Drives the full SDK → /event → Session.updatePart → sync.run →
+// bus.publish → SDK subscriber path. Goes red if either the publisher uses a
+// different bus instance (Bug 2 / pre-#27825) or the stream loses context (Bug 1 /
+// pre-#27425).
+  serverPathParity("streams sync-backed part updates to /event subscribers", (serverPath) =>
+    withStandardProject(serverPath, ({ sdk, directory }) =>
+      Effect.gen(function* () {
+        const session = yield* capture(() => sdk.session.create({ title: "sync-backed part event" }))
+        const sessionID = String(record(session.data).id)
+        const seeded = yield* seedMessage(directory, sessionID)
+
+        const controller = new AbortController()
+        yield* Effect.addFinalizer(() => Effect.sync(() => controller.abort()))
+        const events = yield* call(() => sdk.event.subscribe(undefined, { signal: controller.signal }))
+        yield* Effect.addFinalizer(() =>
+          call(async () => void (await events.stream.return?.(undefined))).pipe(Effect.ignore),
+        )
+
+        const ready = yield* Deferred.make<void>()
+        const received = yield* Deferred.make<unknown>()
+
+        yield* call(async () => {
+          for await (const event of events.stream) {
+            const payload = record(event).payload ?? event
+            const type = record(payload).type
+            if (type === "server.connected") {
+              Deferred.doneUnsafe(ready, Effect.void)
+              continue
+            }
+            if (type === MessageV2.Event.PartUpdated.type) {
+              Deferred.doneUnsafe(received, Effect.succeed(payload))
+              return
+            }
+          }
+        }).pipe(Effect.forkScoped)
+
+        yield* awaitWithTimeout(Deferred.await(ready), "timed out waiting for /event server.connected", "2 seconds")
+
+        const updated = yield* capture(() =>
+          sdk.part.update({
+            sessionID,
+            messageID: seeded.message.id,
+            partID: seeded.part.id,
+            part: { ...seeded.part, text: "updated via sync" } as NonNullable<
+              Parameters<Sdk["part"]["update"]>[0]["part"]
+            >,
+          }),
+        )
+        expect(updated.status).toBe(200)
+
+        const event = yield* awaitWithTimeout(
+          Deferred.await(received),
+          "timed out waiting for message.part.updated bus payload over /event",
+          "5 seconds",
+        )
+        const properties = record(record(event).properties)
+        expect(record(properties.part)).toMatchObject({ id: seeded.part.id, type: "text" })
+        return { type: record(event).type, partType: record(properties.part).type }
+      }),
+    ),
+  )
+
   serverPathParity("matches generated SDK prompt no-reply routes", (serverPath) =>
     withStandardProject(serverPath, ({ sdk }) =>
       Effect.gen(function* () {