diff --git a/packages/opencode/src/session/run-state.ts b/packages/opencode/src/session/run-state.ts
index 9d4986f174..2983521a9e 100644
--- a/packages/opencode/src/session/run-state.ts
+++ b/packages/opencode/src/session/run-state.ts
@@ -1,5 +1,6 @@
 import { InstanceState } from "@/effect/instance-state"
 import { Runner } from "@/effect/runner"
+import { BackgroundJob } from "@/background/job"
 import { Effect, Latch, Layer, Scope, Context } from "effect"
 import * as Session from "./session"
 import { MessageV2 } from "./message-v2"
@@ -27,6 +28,7 @@ export class Service extends Context.Service<Service, Interface>()("@opencode/Se
 export const layer = Layer.effect(
   Service,
   Effect.gen(function* () {
+    const background = yield* BackgroundJob.Service
     const status = yield* SessionStatus.Service
 
     const state = yield* InstanceState.make(
@@ -75,6 +77,7 @@ export const layer = Layer.effect(
     })
 
     const cancel = Effect.fn("SessionRunState.cancel")(function* (sessionID: SessionID) {
+      yield* cancelBackgroundJobs(background, sessionID)
       const data = yield* InstanceState.get(state)
       const existing = data.runners.get(sessionID)
       if (!existing || !existing.busy) {
@@ -105,6 +108,40 @@ export const layer = Layer.effect(
   }),
 )
 
-export const defaultLayer = layer.pipe(Layer.provide(SessionStatus.defaultLayer))
+export const defaultLayer = layer.pipe(Layer.provide(BackgroundJob.defaultLayer), Layer.provide(SessionStatus.defaultLayer))
+
+const cancelBackgroundJobs = Effect.fn("SessionRunState.cancelBackgroundJobs")(function* (
+  background: BackgroundJob.Interface,
+  sessionID: SessionID,
+) {
+  const jobs = yield* background.list()
+  const pending = new Set<string>([sessionID])
+  const cancelled = new Set<string>()
+  const matches = (job: BackgroundJob.Info) => {
+    if (job.status !== "running") return false
+    if (cancelled.has(job.id)) return false
+    if (pending.has(job.id)) return true
+    if (typeof job.metadata?.sessionId === "string" && pending.has(job.metadata.sessionId)) return true
+    return typeof job.metadata?.parentSessionId === "string" && pending.has(job.metadata.parentSessionId)
+  }
+  let batch = jobs.filter(matches)
+  while (batch.length > 0) {
+    yield* Effect.forEach(
+      batch,
+      (job) =>
+        background.cancel(job.id).pipe(
+          Effect.tap(() =>
+            Effect.sync(() => {
+              cancelled.add(job.id)
+              pending.add(job.id)
+              if (typeof job.metadata?.sessionId === "string") pending.add(job.metadata.sessionId)
+            }),
+          ),
+        ),
+      { concurrency: "unbounded", discard: true },
+    )
+    batch = jobs.filter(matches)
+  }
+})
 
 export * as SessionRunState from "./run-state"
diff --git a/packages/opencode/src/session/session.ts b/packages/opencode/src/session/session.ts
index eff027579a..2a6a9dc65c 100644
--- a/packages/opencode/src/session/session.ts
+++ b/packages/opencode/src/session/session.ts
@@ -1,5 +1,6 @@
 import { Slug } from "@opencode-ai/core/util/slug"
 import path from "path"
+import { BackgroundJob } from "@/background/job"
 import { BusEvent } from "@/bus/bus-event"
 import { Bus } from "@/bus"
 import { Decimal } from "decimal.js"
@@ -503,9 +504,10 @@ export type Patch = Types.DeepMutable<SyncEvent.Event<typeof Event.Updated>["dat
 const db = <T>(fn: (d: Parameters<typeof Database.use>[0] extends (trx: infer D) => any ? D : never) => T) =>
   Effect.sync(() => Database.use(fn))
 
-export const layer: Layer.Layer<Service, never, Bus.Service | Storage.Service | SyncEvent.Service> = Layer.effect(
+export const layer: Layer.Layer<Service, never, BackgroundJob.Service | Bus.Service | Storage.Service | SyncEvent.Service> = Layer.effect(
   Service,
   Effect.gen(function* () {
+    const background = yield* BackgroundJob.Service
     const bus = yield* Bus.Service
     const storage = yield* Storage.Service
     const sync = yield* SyncEvent.Service
@@ -583,6 +585,7 @@ export const layer: Layer.Layer<Service, never, Bus.Service | Storage.Service |
     const remove: Interface["remove"] = Effect.fnUntraced(function* (sessionID: SessionID) {
       const session = yield* get(sessionID)
       try {
+        yield* cancelBackgroundJobs(background, sessionID)
         const kids = yield* children(sessionID)
         for (const child of kids) {
           yield* remove(child.id)
@@ -833,11 +836,29 @@ export const layer: Layer.Layer<Service, never, Bus.Service | Storage.Service |
 )
 
 export const defaultLayer = layer.pipe(
+  Layer.provide(BackgroundJob.defaultLayer),
   Layer.provide(Bus.layer),
   Layer.provide(Storage.defaultLayer),
   Layer.provide(SyncEvent.defaultLayer),
 )
 
+const cancelBackgroundJobs = Effect.fn("Session.cancelBackgroundJobs")(function* (
+  background: BackgroundJob.Interface,
+  sessionID: SessionID,
+) {
+  const jobs = yield* background.list()
+  yield* Effect.forEach(
+    jobs.filter((job) => {
+      if (job.status !== "running") return false
+      if (job.id === sessionID) return true
+      if (job.metadata?.sessionId === sessionID) return true
+      return job.metadata?.parentSessionId === sessionID
+    }),
+    (job) => background.cancel(job.id),
+    { concurrency: "unbounded", discard: true },
+  )
+})
+
 function* listByProject(
   input: ListInput & {
     projectID: ProjectID
diff --git a/packages/opencode/test/session/prompt.test.ts b/packages/opencode/test/session/prompt.test.ts
index 3821954945..07615ca5d6 100644
--- a/packages/opencode/test/session/prompt.test.ts
+++ b/packages/opencode/test/session/prompt.test.ts
@@ -7,6 +7,7 @@ import path from "path"
 import { fileURLToPath, pathToFileURL } from "url"
 import { NamedError } from "@opencode-ai/core/util/error"
 import { Agent as AgentSvc } from "../../src/agent/agent"
+import { BackgroundJob } from "@/background/job"
 import { Bus } from "../../src/bus"
 import { Command } from "../../src/command"
 import { Config } from "@/config/config"
@@ -175,6 +176,7 @@ function makeHttp() {
     lsp,
     mcp,
     AppFileSystem.defaultLayer,
+    BackgroundJob.defaultLayer,
     status,
     SyncEvent.defaultLayer,
   ).pipe(Layer.provideMerge(infra))
diff --git a/packages/opencode/test/session/snapshot-tool-race.test.ts b/packages/opencode/test/session/snapshot-tool-race.test.ts
index 8640612e98..292f821c42 100644
--- a/packages/opencode/test/session/snapshot-tool-race.test.ts
+++ b/packages/opencode/test/session/snapshot-tool-race.test.ts
@@ -30,6 +30,7 @@ import { TestLLMServer } from "../lib/llm-server"
 // Same layer setup as prompt-effect.test.ts
 import { NodeFileSystem } from "@effect/platform-node"
 import { Agent as AgentSvc } from "../../src/agent/agent"
+import { BackgroundJob } from "@/background/job"
 import { Git } from "../../src/git"
 import { Bus } from "../../src/bus"
 import { Command } from "../../src/command"
@@ -124,6 +125,7 @@ function makeHttp() {
     lsp,
     mcp,
     AppFileSystem.defaultLayer,
+    BackgroundJob.defaultLayer,
     status,
     SyncEvent.defaultLayer,
   ).pipe(Layer.provideMerge(infra))