diff --git a/packages/opencode/test/tool/task.test.ts b/packages/opencode/test/tool/task.test.ts
index d00f89da75..e2abdc138e 100644
--- a/packages/opencode/test/tool/task.test.ts
+++ b/packages/opencode/test/tool/task.test.ts
@@ -4,6 +4,11 @@ import { Agent } from "../../src/agent/agent"
 import { Config } from "../../src/config/config"
 import * as CrossSpawnSpawner from "../../src/effect/cross-spawn-spawner"
 import { Instance } from "../../src/project/instance"
+import { Session } from "../../src/session"
+import { MessageV2 } from "../../src/session/message-v2"
+import { SessionPrompt } from "../../src/session/prompt"
+import { MessageID, PartID } from "../../src/session/schema"
+import { ModelID, ProviderID } from "../../src/provider/schema"
 import { TaskTool } from "../../src/tool/task"
 import { provideTmpdirInstance } from "../fixture/fixture"
 import { testEffect } from "../lib/effect"
@@ -12,7 +17,73 @@ afterEach(async () => {
   await Instance.disposeAll()
 })
 
-const it = testEffect(Layer.mergeAll(Agent.defaultLayer, Config.defaultLayer, CrossSpawnSpawner.defaultLayer))
+const ref = {
+  providerID: ProviderID.make("test"),
+  modelID: ModelID.make("test-model"),
+}
+
+const it = testEffect(
+  Layer.mergeAll(Agent.defaultLayer, Config.defaultLayer, CrossSpawnSpawner.defaultLayer, Session.defaultLayer),
+)
+
+const seed = Effect.fn("TaskToolTest.seed")(function* (title = "Pinned") {
+  const session = yield* Session.Service
+  const chat = yield* session.create({ title })
+  const user = yield* session.updateMessage({
+    id: MessageID.ascending(),
+    role: "user",
+    sessionID: chat.id,
+    agent: "build",
+    model: ref,
+    time: { created: Date.now() },
+  })
+  const assistant: MessageV2.Assistant = {
+    id: MessageID.ascending(),
+    role: "assistant",
+    parentID: user.id,
+    sessionID: chat.id,
+    mode: "build",
+    agent: "build",
+    cost: 0,
+    path: { cwd: "/tmp", root: "/tmp" },
+    tokens: { input: 0, output: 0, reasoning: 0, cache: { read: 0, write: 0 } },
+    modelID: ref.modelID,
+    providerID: ref.providerID,
+    time: { created: Date.now() },
+  }
+  yield* session.updateMessage(assistant)
+  return { chat, assistant }
+})
+
+function reply(input: Parameters<typeof SessionPrompt.prompt>[0], text: string): MessageV2.WithParts {
+  const id = MessageID.ascending()
+  return {
+    info: {
+      id,
+      role: "assistant",
+      parentID: input.messageID ?? MessageID.ascending(),
+      sessionID: input.sessionID,
+      mode: input.agent ?? "general",
+      agent: input.agent ?? "general",
+      cost: 0,
+      path: { cwd: "/tmp", root: "/tmp" },
+      tokens: { input: 0, output: 0, reasoning: 0, cache: { read: 0, write: 0 } },
+      modelID: input.model?.modelID ?? ref.modelID,
+      providerID: input.model?.providerID ?? ref.providerID,
+      time: { created: Date.now() },
+      finish: "stop",
+    },
+    parts: [
+      {
+        id: PartID.ascending(),
+        messageID: id,
+        sessionID: input.sessionID,
+        type: "text",
+        text,
+      },
+    ],
+  }
+}
 
 describe("tool.task", () => {
   it.live("description sorts subagents by name and is stable across calls", () =>
@@ -53,4 +124,144 @@ describe("tool.task", () => {
       },
     ),
   )
+
+  it.live("execute resumes an existing task session from task_id", () =>
+    provideTmpdirInstance(() =>
+      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* Effect.promise(() => tool.init())
+        const resolve = SessionPrompt.resolvePromptParts
+        const prompt = SessionPrompt.prompt
+        let seen: Parameters<typeof SessionPrompt.prompt>[0] | undefined
+
+        SessionPrompt.resolvePromptParts = async (template) => [{ type: "text", text: template }]
+        SessionPrompt.prompt = async (input) => {
+          seen = input
+          return reply(input, "resumed")
+        }
+        yield* Effect.addFinalizer(() =>
+          Effect.sync(() => {
+            SessionPrompt.resolvePromptParts = resolve
+            SessionPrompt.prompt = prompt
+          }),
+        )
+
+        const result = yield* Effect.promise(() =>
+          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,
+              messages: [],
+              metadata() {},
+              ask: async () => {},
+            },
+          ),
+        )
+
+        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 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* Effect.promise(() => tool.init())
+          const resolve = SessionPrompt.resolvePromptParts
+          const prompt = SessionPrompt.prompt
+          let seen: Parameters<typeof SessionPrompt.prompt>[0] | undefined
+
+          SessionPrompt.resolvePromptParts = async (template) => [{ type: "text", text: template }]
+          SessionPrompt.prompt = async (input) => {
+            seen = input
+            return reply(input, "done")
+          }
+          yield* Effect.addFinalizer(() =>
+            Effect.sync(() => {
+              SessionPrompt.resolvePromptParts = resolve
+              SessionPrompt.prompt = prompt
+            }),
+          )
+
+          const result = yield* Effect.promise(() =>
+            def.execute(
+              {
+                description: "inspect bug",
+                prompt: "look into the cache key path",
+                subagent_type: "reviewer",
+              },
+              {
+                sessionID: chat.id,
+                messageID: assistant.id,
+                agent: "build",
+                abort: new AbortController().signal,
+                messages: [],
+                metadata() {},
+                ask: async () => {},
+              },
+            ),
+          )
+
+          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"],
+          },
+        },
+      },
+    ),
+  )
 })