diff --git a/packages/opencode/src/session/prompt.ts b/packages/opencode/src/session/prompt.ts
index e1fa81abf1..8286ecf8e6 100644
--- a/packages/opencode/src/session/prompt.ts
+++ b/packages/opencode/src/session/prompt.ts
@@ -1,6 +1,5 @@
 import path from "path"
 import os from "os"
-import z from "zod"
 import * as EffectZod from "@/util/effect-zod"
 import { SessionID, MessageID, PartID } from "./schema"
 import { MessageV2 } from "./message-v2"
@@ -121,9 +120,8 @@ export const layer = Layer.effect(
       return yield* EffectBridge.make()
     })
     const ops = Effect.fn("SessionPrompt.ops")(function* () {
-      const run = yield* runner()
       return {
-        cancel: (sessionID: SessionID) => run.fork(cancel(sessionID)),
+        cancel: (sessionID: SessionID) => cancel(sessionID),
         resolvePromptParts: (template: string) => resolvePromptParts(template),
         prompt: (input: PromptInput) => prompt(input),
       } satisfies TaskPromptOps
diff --git a/packages/opencode/src/tool/task.ts b/packages/opencode/src/tool/task.ts
index e58ea9b122..22e4e5671c 100644
--- a/packages/opencode/src/tool/task.ts
+++ b/packages/opencode/src/tool/task.ts
@@ -6,10 +6,11 @@ import { MessageV2 } from "../session/message-v2"
 import { Agent } from "../agent/agent"
 import type { SessionPrompt } from "../session/prompt"
 import { Config } from "@/config/config"
-import { Effect, Schema } from "effect"
+import { Effect, Exit, Schema } from "effect"
+import { EffectBridge } from "@/effect/bridge"
 
 export interface TaskPromptOps {
-  cancel(sessionID: SessionID): void
+  cancel(sessionID: SessionID): Effect.Effect<void>
   resolvePromptParts(template: string): Effect.Effect<SessionPrompt.PromptInput["parts"]>
   prompt(input: SessionPrompt.PromptInput): Effect.Effect<MessageV2.WithParts>
 }
@@ -118,16 +119,18 @@ export const TaskTool = Tool.define(
 
       const ops = ctx.extra?.promptOps as TaskPromptOps
       if (!ops) return yield* Effect.fail(new Error("TaskTool requires promptOps in ctx.extra"))
+      const runCancel = yield* EffectBridge.make()
 
       const messageID = MessageID.ascending()
+      const cancel = ops.cancel(nextSession.id)
 
-      function cancel() {
-        ops.cancel(nextSession.id)
+      function onAbort() {
+        runCancel.fork(cancel)
       }
 
       return yield* Effect.acquireUseRelease(
         Effect.sync(() => {
-          ctx.abort.addEventListener("abort", cancel)
+          ctx.abort.addEventListener("abort", onAbort)
         }),
         () =>
           Effect.gen(function* () {
@@ -163,10 +166,16 @@ export const TaskTool = Tool.define(
               ].join("\n"),
             }
           }),
-        () =>
-          Effect.sync(() => {
-            ctx.abort.removeEventListener("abort", cancel)
-          }),
+        (_, exit) =>
+          Effect.gen(function* () {
+            if (Exit.hasInterrupts(exit)) yield* cancel
+          }).pipe(
+            Effect.ensuring(
+              Effect.sync(() => {
+                ctx.abort.removeEventListener("abort", onAbort)
+              }),
+            ),
+          ),
       )
     })
 
diff --git a/packages/opencode/test/session/prompt.test.ts b/packages/opencode/test/session/prompt.test.ts
index a602c0c8d7..c5170f3464 100644
--- a/packages/opencode/test/session/prompt.test.ts
+++ b/packages/opencode/test/session/prompt.test.ts
@@ -858,6 +858,43 @@ it.live(
   30_000,
 )
 
+it.live(
+  "cancel propagates from slash command subtask to child session",
+  () =>
+    provideTmpdirServer(
+      Effect.fnUntraced(function* ({ llm }) {
+        const prompt = yield* SessionPrompt.Service
+        const sessions = yield* Session.Service
+        const status = yield* SessionStatus.Service
+        const chat = yield* sessions.create({ title: "Pinned" })
+        yield* llm.hang
+        const msg = yield* user(chat.id, "hello")
+        yield* addSubtask(chat.id, msg.id)
+
+        const fiber = yield* prompt.loop({ sessionID: chat.id }).pipe(Effect.forkChild)
+        yield* llm.wait(1)
+
+        const msgs = yield* MessageV2.filterCompactedEffect(chat.id)
+        const taskMsg = msgs.find((item) => item.info.role === "assistant" && item.info.agent === "general")
+        const tool = taskMsg ? toolPart(taskMsg.parts) : undefined
+        const sessionID = tool?.state.status === "running" ? tool.state.metadata?.sessionId : undefined
+        expect(typeof sessionID).toBe("string")
+        if (typeof sessionID !== "string") throw new Error("missing child session id")
+        const childID = SessionID.make(sessionID)
+        expect((yield* status.get(childID)).type).toBe("busy")
+
+        yield* prompt.cancel(chat.id)
+        const exit = yield* Fiber.await(fiber)
+        expect(Exit.isSuccess(exit)).toBe(true)
+
+        expect((yield* status.get(chat.id)).type).toBe("idle")
+        expect((yield* status.get(childID)).type).toBe("idle")
+      }),
+      { git: true, config: providerCfg },
+    ),
+  10_000,
+)
+
 it.live(
   "cancel with queued callers resolves all cleanly",
   () =>
diff --git a/packages/opencode/test/tool/task.test.ts b/packages/opencode/test/tool/task.test.ts
index a8d62bb68c..f75fcf84b8 100644
--- a/packages/opencode/test/tool/task.test.ts
+++ b/packages/opencode/test/tool/task.test.ts
@@ -1,18 +1,17 @@
 import { afterEach, describe, expect } from "bun:test"
-import { Effect, Layer } from "effect"
+import { Effect, Exit, Fiber, Layer } from "effect"
 import { Agent } from "../../src/agent/agent"
 import { Config } from "@/config/config"
 import { CrossSpawnSpawner } from "@opencode-ai/core/cross-spawn-spawner"
-import { Instance } from "../../src/project/instance"
 import { Session } from "@/session/session"
 import { MessageV2 } from "../../src/session/message-v2"
 import type { SessionPrompt } from "../../src/session/prompt"
-import { MessageID, PartID } from "../../src/session/schema"
+import { MessageID, PartID, SessionID } from "../../src/session/schema"
 import { ModelID, ProviderID } from "../../src/provider/schema"
 import { TaskTool, type TaskPromptOps } from "../../src/tool/task"
 import { Truncate } from "@/tool/truncate"
 import { ToolRegistry } from "@/tool/registry"
-import { disposeAllInstances, provideTmpdirInstance } from "../fixture/fixture"
+import { disposeAllInstances } from "../fixture/fixture"
 import { testEffect } from "../lib/effect"
 
 afterEach(async () => {
@@ -35,6 +34,14 @@ const it = testEffect(
   ),
 )
 
+function defer<T>() {
+  let resolve!: (value: T | PromiseLike<T>) => void
+  const promise = new Promise<T>((done) => {
+    resolve = done
+  })
+  return { promise, resolve }
+}
+
 const seed = Effect.fn("TaskToolTest.seed")(function* (title = "Pinned") {
   const session = yield* Session.Service
   const chat = yield* session.create({ title })
@@ -66,7 +73,7 @@ const seed = Effect.fn("TaskToolTest.seed")(function* (title = "Pinned") {
 
 function stubOps(opts?: { onPrompt?: (input: SessionPrompt.PromptInput) => void; text?: string }): TaskPromptOps {
   return {
-    cancel() {},
+    cancel: () => Effect.void,
     resolvePromptParts: (template) => Effect.succeed([{ type: "text" as const, text: template }]),
     prompt: (input) =>
       Effect.sync(() => {
@@ -107,102 +114,270 @@ function reply(input: SessionPrompt.PromptInput, text: string): MessageV2.WithPa
 }
 
 describe("tool.task", () => {
-  it.live("description sorts subagents by name and is stable across calls", () =>
-    provideTmpdirInstance(
-      () =>
-        Effect.gen(function* () {
-          const agent = yield* Agent.Service
-          const build = yield* agent.get("build")
-          const registry = yield* ToolRegistry.Service
-          const get = Effect.fnUntraced(function* () {
-            const tools = yield* registry.tools({ ...ref, agent: build })
-            return tools.find((tool) => tool.id === TaskTool.id)?.description ?? ""
-          })
-          const first = yield* get()
-          const second = yield* get()
+  it.instance(
+    "description sorts subagents by name and is stable across calls",
+    () =>
+      Effect.gen(function* () {
+        const agent = yield* Agent.Service
+        const build = yield* agent.get("build")
+        const registry = yield* ToolRegistry.Service
+        const get = Effect.fnUntraced(function* () {
+          const tools = yield* registry.tools({ ...ref, agent: build })
+          return tools.find((tool) => tool.id === TaskTool.id)?.description ?? ""
+        })
+        const first = yield* get()
+        const second = yield* get()
 
-          expect(first).toBe(second)
+        expect(first).toBe(second)
 
-          const alpha = first.indexOf("- alpha: Alpha agent")
-          const explore = first.indexOf("- explore:")
-          const general = first.indexOf("- general:")
-          const zebra = first.indexOf("- zebra: Zebra agent")
+        const alpha = first.indexOf("- alpha: Alpha agent")
+        const explore = first.indexOf("- explore:")
+        const general = first.indexOf("- general:")
+        const zebra = first.indexOf("- zebra: Zebra agent")
 
-          expect(alpha).toBeGreaterThan(-1)
-          expect(explore).toBeGreaterThan(alpha)
-          expect(general).toBeGreaterThan(explore)
-          expect(zebra).toBeGreaterThan(general)
-        }),
-      {
-        config: {
-          agent: {
-            zebra: {
-              description: "Zebra agent",
-              mode: "subagent",
-            },
-            alpha: {
-              description: "Alpha agent",
-              mode: "subagent",
-            },
+        expect(alpha).toBeGreaterThan(-1)
+        expect(explore).toBeGreaterThan(alpha)
+        expect(general).toBeGreaterThan(explore)
+        expect(zebra).toBeGreaterThan(general)
+      }),
+    {
+      config: {
+        agent: {
+          zebra: {
+            description: "Zebra agent",
+            mode: "subagent",
+          },
+          alpha: {
+            description: "Alpha agent",
+            mode: "subagent",
           },
         },
       },
-    ),
+    },
   )
 
-  it.live("description hides denied subagents for the caller", () =>
-    provideTmpdirInstance(
-      () =>
-        Effect.gen(function* () {
-          const agent = yield* Agent.Service
-          const build = yield* agent.get("build")
-          const registry = yield* ToolRegistry.Service
-          const description =
-            (yield* registry.tools({ ...ref, agent: build })).find((tool) => tool.id === TaskTool.id)?.description ?? ""
+  it.instance(
+    "description hides denied subagents for the caller",
+    () =>
+      Effect.gen(function* () {
+        const agent = yield* Agent.Service
+        const build = yield* agent.get("build")
+        const registry = yield* ToolRegistry.Service
+        const description =
+          (yield* registry.tools({ ...ref, agent: build })).find((tool) => tool.id === TaskTool.id)?.description ?? ""
 
-          expect(description).toContain("- alpha: Alpha agent")
-          expect(description).not.toContain("- zebra: Zebra agent")
-        }),
-      {
-        config: {
-          permission: {
-            task: {
-              "*": "allow",
-              zebra: "deny",
-            },
+        expect(description).toContain("- alpha: Alpha agent")
+        expect(description).not.toContain("- zebra: Zebra agent")
+      }),
+    {
+      config: {
+        permission: {
+          task: {
+            "*": "allow",
+            zebra: "deny",
           },
-          agent: {
-            zebra: {
-              description: "Zebra agent",
-              mode: "subagent",
-            },
-            alpha: {
-              description: "Alpha agent",
-              mode: "subagent",
-            },
+        },
+        agent: {
+          zebra: {
+            description: "Zebra agent",
+            mode: "subagent",
+          },
+          alpha: {
+            description: "Alpha agent",
+            mode: "subagent",
           },
         },
       },
-    ),
+    },
   )
 
-  it.live("execute resumes an existing task session from task_id", () =>
-    provideTmpdirInstance(() =>
+  it.instance("execute resumes an existing task session from task_id", () =>
+    Effect.gen(function* () {
+      const sessions = yield* Session.Service
+      const { chat, assistant } = yield* seed()
+      const child = yield* sessions.create({ parentID: chat.id, title: "Existing child" })
+      const tool = yield* TaskTool
+      const def = yield* tool.init()
+      let seen: SessionPrompt.PromptInput | undefined
+      const promptOps = stubOps({ text: "resumed", onPrompt: (input) => (seen = input) })
+
+      const result = yield* def.execute(
+        {
+          description: "inspect bug",
+          prompt: "look into the cache key path",
+          subagent_type: "general",
+          task_id: child.id,
+        },
+        {
+          sessionID: chat.id,
+          messageID: assistant.id,
+          agent: "build",
+          abort: new AbortController().signal,
+          extra: { promptOps },
+          messages: [],
+          metadata: () => Effect.void,
+          ask: () => Effect.void,
+        },
+      )
+
+      const kids = yield* sessions.children(chat.id)
+      expect(kids).toHaveLength(1)
+      expect(kids[0]?.id).toBe(child.id)
+      expect(result.metadata.sessionId).toBe(child.id)
+      expect(result.output).toContain(`task_id: ${child.id}`)
+      expect(seen?.sessionID).toBe(child.id)
+    }),
+  )
+
+  it.instance("execute asks by default and skips checks when bypassed", () =>
+    Effect.gen(function* () {
+      const { chat, assistant } = yield* seed()
+      const tool = yield* TaskTool
+      const def = yield* tool.init()
+      const calls: unknown[] = []
+      const promptOps = stubOps()
+
+      const exec = (extra?: Record<string, any>) =>
+        def.execute(
+          {
+            description: "inspect bug",
+            prompt: "look into the cache key path",
+            subagent_type: "general",
+          },
+          {
+            sessionID: chat.id,
+            messageID: assistant.id,
+            agent: "build",
+            abort: new AbortController().signal,
+            extra: { promptOps, ...extra },
+            messages: [],
+            metadata: () => Effect.void,
+            ask: (input) =>
+              Effect.sync(() => {
+                calls.push(input)
+              }),
+          },
+        )
+
+      yield* exec()
+      yield* exec({ bypassAgentCheck: true })
+
+      expect(calls).toHaveLength(1)
+      expect(calls[0]).toEqual({
+        permission: "task",
+        patterns: ["general"],
+        always: ["*"],
+        metadata: {
+          description: "inspect bug",
+          subagent_type: "general",
+        },
+      })
+    }),
+  )
+
+  it.instance("execute cancels child session when abort signal fires", () =>
+    Effect.gen(function* () {
+      const { chat, assistant } = yield* seed()
+      const tool = yield* TaskTool
+      const def = yield* tool.init()
+      const ready = defer<SessionPrompt.PromptInput>()
+      const cancelled = defer<SessionID>()
+      const abort = new AbortController()
+      const promptOps: TaskPromptOps = {
+        cancel: (sessionID) =>
+          Effect.sync(() => {
+            cancelled.resolve(sessionID)
+          }),
+        resolvePromptParts: (template) => Effect.succeed([{ type: "text" as const, text: template }]),
+        prompt: (input) =>
+          Effect.promise(() => {
+            ready.resolve(input)
+            return cancelled.promise
+          }).pipe(Effect.as(reply(input, "cancelled"))),
+      }
+
+      const fiber = yield* def
+        .execute(
+          {
+            description: "inspect bug",
+            prompt: "look into the cache key path",
+            subagent_type: "general",
+          },
+          {
+            sessionID: chat.id,
+            messageID: assistant.id,
+            agent: "build",
+            abort: abort.signal,
+            extra: { promptOps },
+            messages: [],
+            metadata: () => Effect.void,
+            ask: () => Effect.void,
+          },
+        )
+        .pipe(Effect.forkChild)
+
+      const input = yield* Effect.promise(() => ready.promise)
+      abort.abort()
+      expect(yield* Effect.promise(() => cancelled.promise)).toBe(input.sessionID)
+
+      const exit = yield* Fiber.await(fiber)
+      expect(Exit.isSuccess(exit)).toBe(true)
+    }),
+  )
+
+  it.instance("execute creates a child when task_id does not exist", () =>
+    Effect.gen(function* () {
+      const sessions = yield* Session.Service
+      const { chat, assistant } = yield* seed()
+      const tool = yield* TaskTool
+      const def = yield* tool.init()
+      let seen: SessionPrompt.PromptInput | undefined
+      const promptOps = stubOps({ text: "created", onPrompt: (input) => (seen = input) })
+
+      const result = yield* def.execute(
+        {
+          description: "inspect bug",
+          prompt: "look into the cache key path",
+          subagent_type: "general",
+          task_id: "ses_missing",
+        },
+        {
+          sessionID: chat.id,
+          messageID: assistant.id,
+          agent: "build",
+          abort: new AbortController().signal,
+          extra: { promptOps },
+          messages: [],
+          metadata: () => Effect.void,
+          ask: () => Effect.void,
+        },
+      )
+
+      const kids = yield* sessions.children(chat.id)
+      expect(kids).toHaveLength(1)
+      expect(kids[0]?.id).toBe(result.metadata.sessionId)
+      expect(result.metadata.sessionId).not.toBe("ses_missing")
+      expect(result.output).toContain(`task_id: ${result.metadata.sessionId}`)
+      expect(seen?.sessionID).toBe(result.metadata.sessionId)
+    }),
+  )
+
+  it.instance(
+    "execute shapes child permissions for task, todowrite, and primary tools",
+    () =>
       Effect.gen(function* () {
         const sessions = yield* Session.Service
         const { chat, assistant } = yield* seed()
-        const child = yield* sessions.create({ parentID: chat.id, title: "Existing child" })
         const tool = yield* TaskTool
         const def = yield* tool.init()
         let seen: SessionPrompt.PromptInput | undefined
-        const promptOps = stubOps({ text: "resumed", onPrompt: (input) => (seen = input) })
+        const promptOps = stubOps({ onPrompt: (input) => (seen = input) })
 
         const result = yield* def.execute(
           {
             description: "inspect bug",
             prompt: "look into the cache key path",
-            subagent_type: "general",
-            task_id: child.id,
+            subagent_type: "reviewer",
           },
           {
             sessionID: chat.id,
@@ -216,172 +391,45 @@ describe("tool.task", () => {
           },
         )
 
-        const kids = yield* sessions.children(chat.id)
-        expect(kids).toHaveLength(1)
-        expect(kids[0]?.id).toBe(child.id)
-        expect(result.metadata.sessionId).toBe(child.id)
-        expect(result.output).toContain(`task_id: ${child.id}`)
-        expect(seen?.sessionID).toBe(child.id)
-      }),
-    ),
-  )
-
-  it.live("execute asks by default and skips checks when bypassed", () =>
-    provideTmpdirInstance(() =>
-      Effect.gen(function* () {
-        const { chat, assistant } = yield* seed()
-        const tool = yield* TaskTool
-        const def = yield* tool.init()
-        const calls: unknown[] = []
-        const promptOps = stubOps()
-
-        const exec = (extra?: Record<string, any>) =>
-          def.execute(
-            {
-              description: "inspect bug",
-              prompt: "look into the cache key path",
-              subagent_type: "general",
-            },
-            {
-              sessionID: chat.id,
-              messageID: assistant.id,
-              agent: "build",
-              abort: new AbortController().signal,
-              extra: { promptOps, ...extra },
-              messages: [],
-              metadata: () => Effect.void,
-              ask: (input) =>
-                Effect.sync(() => {
-                  calls.push(input)
-                }),
-            },
-          )
-
-        yield* exec()
-        yield* exec({ bypassAgentCheck: true })
-
-        expect(calls).toHaveLength(1)
-        expect(calls[0]).toEqual({
-          permission: "task",
-          patterns: ["general"],
-          always: ["*"],
-          metadata: {
-            description: "inspect bug",
-            subagent_type: "general",
+        const child = yield* sessions.get(result.metadata.sessionId)
+        expect(child.parentID).toBe(chat.id)
+        expect(child.permission).toEqual([
+          {
+            permission: "todowrite",
+            pattern: "*",
+            action: "deny",
           },
+          {
+            permission: "bash",
+            pattern: "*",
+            action: "allow",
+          },
+          {
+            permission: "read",
+            pattern: "*",
+            action: "allow",
+          },
+        ])
+        expect(seen?.tools).toEqual({
+          todowrite: false,
+          bash: false,
+          read: false,
         })
       }),
-    ),
-  )
-
-  it.live("execute creates a child when task_id does not exist", () =>
-    provideTmpdirInstance(() =>
-      Effect.gen(function* () {
-        const sessions = yield* Session.Service
-        const { chat, assistant } = yield* seed()
-        const tool = yield* TaskTool
-        const def = yield* tool.init()
-        let seen: SessionPrompt.PromptInput | undefined
-        const promptOps = stubOps({ text: "created", onPrompt: (input) => (seen = input) })
-
-        const result = yield* def.execute(
-          {
-            description: "inspect bug",
-            prompt: "look into the cache key path",
-            subagent_type: "general",
-            task_id: "ses_missing",
-          },
-          {
-            sessionID: chat.id,
-            messageID: assistant.id,
-            agent: "build",
-            abort: new AbortController().signal,
-            extra: { promptOps },
-            messages: [],
-            metadata: () => Effect.void,
-            ask: () => Effect.void,
-          },
-        )
-
-        const kids = yield* sessions.children(chat.id)
-        expect(kids).toHaveLength(1)
-        expect(kids[0]?.id).toBe(result.metadata.sessionId)
-        expect(result.metadata.sessionId).not.toBe("ses_missing")
-        expect(result.output).toContain(`task_id: ${result.metadata.sessionId}`)
-        expect(seen?.sessionID).toBe(result.metadata.sessionId)
-      }),
-    ),
-  )
-
-  it.live("execute shapes child permissions for task, todowrite, and primary tools", () =>
-    provideTmpdirInstance(
-      () =>
-        Effect.gen(function* () {
-          const sessions = yield* Session.Service
-          const { chat, assistant } = yield* seed()
-          const tool = yield* TaskTool
-          const def = yield* tool.init()
-          let seen: SessionPrompt.PromptInput | undefined
-          const promptOps = stubOps({ onPrompt: (input) => (seen = input) })
-
-          const result = yield* def.execute(
-            {
-              description: "inspect bug",
-              prompt: "look into the cache key path",
-              subagent_type: "reviewer",
+    {
+      config: {
+        agent: {
+          reviewer: {
+            mode: "subagent",
+            permission: {
+              task: "allow",
             },
-            {
-              sessionID: chat.id,
-              messageID: assistant.id,
-              agent: "build",
-              abort: new AbortController().signal,
-              extra: { promptOps },
-              messages: [],
-              metadata: () => Effect.void,
-              ask: () => Effect.void,
-            },
-          )
-
-          const child = yield* sessions.get(result.metadata.sessionId)
-          expect(child.parentID).toBe(chat.id)
-          expect(child.permission).toEqual([
-            {
-              permission: "todowrite",
-              pattern: "*",
-              action: "deny",
-            },
-            {
-              permission: "bash",
-              pattern: "*",
-              action: "allow",
-            },
-            {
-              permission: "read",
-              pattern: "*",
-              action: "allow",
-            },
-          ])
-          expect(seen?.tools).toEqual({
-            todowrite: false,
-            bash: false,
-            read: false,
-          })
-        }),
-      {
-        config: {
-          agent: {
-            reviewer: {
-              mode: "subagent",
-              permission: {
-                task: "allow",
-              },
-            },
-          },
-          experimental: {
-            primary_tools: ["bash", "read"],
           },
         },
+        experimental: {
+          primary_tools: ["bash", "read"],
+        },
       },
-    ),
+    },
   )
 })