From 971c837ad479c21950f7ec0b3dcfb2a5e7b24c40 Mon Sep 17 00:00:00 2001
From: Shoubhit Dash <shoubhit2005@gmail.com>
Date: Fri, 24 Apr 2026 20:08:24 +0530
Subject: [PATCH 1/6] feat(task): add background subagent support

---
 packages/opencode/src/session/prompt.ts       |   4 +
 packages/opencode/src/tool/registry.ts        |  11 +-
 packages/opencode/src/tool/task.ts            | 182 +++++++++---
 packages/opencode/src/tool/task.txt           |  12 +-
 packages/opencode/src/tool/task_status.ts     | 145 +++++++++
 packages/opencode/src/tool/task_status.txt    |  13 +
 packages/opencode/test/tool/task.test.ts      | 185 +++++++++++-
 .../opencode/test/tool/task_status.test.ts    | 278 ++++++++++++++++++
 8 files changed, 775 insertions(+), 55 deletions(-)
 create mode 100644 packages/opencode/src/tool/task_status.ts
 create mode 100644 packages/opencode/src/tool/task_status.txt
 create mode 100644 packages/opencode/test/tool/task_status.test.ts

diff --git a/packages/opencode/src/session/prompt.ts b/packages/opencode/src/session/prompt.ts
index 5f3530bcef..c96f655bd0 100644
--- a/packages/opencode/src/session/prompt.ts
+++ b/packages/opencode/src/session/prompt.ts
@@ -115,6 +115,10 @@ export const layer = Layer.effect(
         cancel: (sessionID: SessionID) => run.fork(cancel(sessionID)),
         resolvePromptParts: (template: string) => resolvePromptParts(template),
         prompt: (input: PromptInput) => prompt(input),
+        loop: (input: LoopInput) => loop(input),
+        fork: (effect: Effect.Effect<void, never, never>) => {
+          run.fork(effect)
+        },
       } satisfies TaskPromptOps
     })
 
diff --git a/packages/opencode/src/tool/registry.ts b/packages/opencode/src/tool/registry.ts
index 539ad63202..eb0c75c7ac 100644
--- a/packages/opencode/src/tool/registry.ts
+++ b/packages/opencode/src/tool/registry.ts
@@ -7,6 +7,7 @@ import { GlobTool } from "./glob"
 import { GrepTool } from "./grep"
 import { ReadTool } from "./read"
 import { TaskTool } from "./task"
+import { TaskStatusTool } from "./task_status"
 import { TodoWriteTool } from "./todo"
 import { WebFetchTool } from "./webfetch"
 import { WriteTool } from "./write"
@@ -47,6 +48,7 @@ import { Bus } from "../bus"
 import { Agent } from "../agent/agent"
 import { Skill } from "../skill"
 import { Permission } from "@/permission"
+import { SessionStatus } from "@/session/status"
 
 const log = Log.create({ service: "tool.registry" })
 
@@ -78,8 +80,9 @@ export const layer: Layer.Layer<
   | Todo.Service
   | Agent.Service
   | Skill.Service
-  | Session.Service
-  | Provider.Service
+   | Session.Service
+   | SessionStatus.Service
+   | Provider.Service
   | LSP.Service
   | Instruction.Service
   | AppFileSystem.Service
@@ -115,6 +118,7 @@ export const layer: Layer.Layer<
     const greptool = yield* GrepTool
     const patchtool = yield* ApplyPatchTool
     const skilltool = yield* SkillTool
+    const taskstatus = yield* TaskStatusTool
     const agent = yield* Agent.Service
 
     const state = yield* InstanceState.make<State>(
@@ -195,6 +199,7 @@ export const layer: Layer.Layer<
           edit: Tool.init(edit),
           write: Tool.init(writetool),
           task: Tool.init(task),
+          taskstatus: Tool.init(taskstatus),
           fetch: Tool.init(webfetch),
           todo: Tool.init(todo),
           search: Tool.init(websearch),
@@ -218,6 +223,7 @@ export const layer: Layer.Layer<
             tool.edit,
             tool.write,
             tool.task,
+            tool.taskstatus,
             tool.fetch,
             tool.todo,
             tool.search,
@@ -335,6 +341,7 @@ export const defaultLayer = Layer.suspend(() =>
     Layer.provide(Skill.defaultLayer),
     Layer.provide(Agent.defaultLayer),
     Layer.provide(Session.defaultLayer),
+    Layer.provide(SessionStatus.defaultLayer),
     Layer.provide(Provider.defaultLayer),
     Layer.provide(LSP.defaultLayer),
     Layer.provide(Instruction.defaultLayer),
diff --git a/packages/opencode/src/tool/task.ts b/packages/opencode/src/tool/task.ts
index 5cb0dc6a83..2bc58cdbb4 100644
--- a/packages/opencode/src/tool/task.ts
+++ b/packages/opencode/src/tool/task.ts
@@ -1,17 +1,22 @@
 import * as Tool from "./tool"
 import DESCRIPTION from "./task.txt"
+import { Bus } from "../bus"
 import { Session } from "../session"
 import { SessionID, MessageID } from "../session/schema"
 import { MessageV2 } from "../session/message-v2"
 import { Agent } from "../agent/agent"
 import type { SessionPrompt } from "../session/prompt"
+import { SessionStatus } from "../session/status"
 import { Config } from "../config"
-import { Effect, Schema } from "effect"
+import { TuiEvent } from "@/cli/cmd/tui/event"
+import { Cause, Effect, Option, Schema } from "effect"
 
 export interface TaskPromptOps {
   cancel(sessionID: SessionID): void
   resolvePromptParts(template: string): Effect.Effect<SessionPrompt.PromptInput["parts"]>
   prompt(input: SessionPrompt.PromptInput): Effect.Effect<MessageV2.WithParts>
+  loop(input: SessionPrompt.LoopInput): Effect.Effect<MessageV2.WithParts>
+  fork(effect: Effect.Effect<void, never, never>): void
 }
 
 const id = "task"
@@ -20,19 +25,61 @@ export const Parameters = Schema.Struct({
   description: Schema.String.annotate({ description: "A short (3-5 words) description of the task" }),
   prompt: Schema.String.annotate({ description: "The task for the agent to perform" }),
   subagent_type: Schema.String.annotate({ description: "The type of specialized agent to use for this task" }),
-  task_id: Schema.optional(Schema.String).annotate({
+  task_id: Schema.optional(SessionID).annotate({
     description:
       "This should only be set if you mean to resume a previous task (you can pass a prior task_id and the task will continue the same subagent session as before instead of creating a fresh one)",
   }),
   command: Schema.optional(Schema.String).annotate({ description: "The command that triggered this task" }),
+  background: Schema.optional(Schema.Boolean).annotate({
+    description: "When true, launch the subagent in the background and return immediately",
+  }),
 })
 
+function output(sessionID: SessionID, text: string) {
+  return [
+    `task_id: ${sessionID} (for resuming to continue this task if needed)`,
+    "",
+    "<task_result>",
+    text,
+    "</task_result>",
+  ].join("\n")
+}
+
+function backgroundOutput(sessionID: SessionID) {
+  return [
+    `task_id: ${sessionID} (for polling this task with task_status)`,
+    "state: running",
+    "",
+    "<task_result>",
+    "Background task started. Continue your current work and call task_status when you need the result.",
+    "</task_result>",
+  ].join("\n")
+}
+
+function backgroundMessage(input: { sessionID: SessionID; description: string; state: "completed" | "error"; text: string }) {
+  const tag = input.state === "completed" ? "task_result" : "task_error"
+  const title =
+    input.state === "completed"
+      ? `Background task completed: ${input.description}`
+      : `Background task failed: ${input.description}`
+  return [title, `task_id: ${input.sessionID}`, `state: ${input.state}`, `<${tag}>`, input.text, `</${tag}>`].join(
+    "\n",
+  )
+}
+
+function errorText(error: unknown) {
+  if (error instanceof Error) return error.message
+  return String(error)
+}
+
 export const TaskTool = Tool.define(
   id,
   Effect.gen(function* () {
     const agent = yield* Agent.Service
+    const bus = yield* Bus.Service
     const config = yield* Config.Service
     const sessions = yield* Session.Service
+    const status = yield* SessionStatus.Service
 
     const run = Effect.fn("TaskTool.execute")(function* (
       params: Schema.Schema.Type<typeof Parameters>,
@@ -62,7 +109,7 @@ export const TaskTool = Tool.define(
 
       const taskID = params.task_id
       const session = taskID
-        ? yield* sessions.get(SessionID.make(taskID)).pipe(Effect.catchCause(() => Effect.succeed(undefined)))
+        ? yield* sessions.get(taskID).pipe(Effect.catchCause(() => Effect.succeed(undefined)))
         : undefined
       const nextSession =
         session ??
@@ -103,19 +150,107 @@ export const TaskTool = Tool.define(
         modelID: msg.info.modelID,
         providerID: msg.info.providerID,
       }
+      const parentModel = {
+        modelID: msg.info.modelID,
+        providerID: msg.info.providerID,
+      }
+      const background = params.background === true
+
+      const metadata = {
+        sessionId: nextSession.id,
+        model,
+        ...(background ? { background: true } : {}),
+      }
 
       yield* ctx.metadata({
         title: params.description,
-        metadata: {
-          sessionId: nextSession.id,
-          model,
-        },
+        metadata,
       })
 
       const ops = ctx.extra?.promptOps as TaskPromptOps
       if (!ops) return yield* Effect.fail(new Error("TaskTool requires promptOps in ctx.extra"))
 
-      const messageID = MessageID.ascending()
+      const runTask = Effect.fn("TaskTool.runTask")(function* () {
+        const parts = yield* ops.resolvePromptParts(params.prompt)
+        const result = yield* ops.prompt({
+          messageID: MessageID.ascending(),
+          sessionID: nextSession.id,
+          model: {
+            modelID: model.modelID,
+            providerID: model.providerID,
+          },
+          agent: next.name,
+          tools: {
+            ...(canTodo ? {} : { todowrite: false }),
+            ...(canTask ? {} : { task: false }),
+            ...Object.fromEntries((cfg.experimental?.primary_tools ?? []).map((item) => [item, false])),
+          },
+          parts,
+        })
+        return result.parts.findLast((item) => item.type === "text")?.text ?? ""
+      })
+
+      const continueIfIdle = Effect.fn("TaskTool.continueIfIdle")(function* (input: {
+        userID: MessageID
+        state: "completed" | "error"
+      }) {
+        if ((yield* status.get(ctx.sessionID)).type !== "idle") return
+        const latest = yield* sessions.findMessage(ctx.sessionID, (item) => item.info.role === "user")
+        if (Option.isNone(latest)) return
+        if (latest.value.info.id !== input.userID) return
+        yield* bus.publish(TuiEvent.ToastShow, {
+          title: input.state === "completed" ? "Background task complete" : "Background task failed",
+          message:
+            input.state === "completed"
+              ? `Background task \"${params.description}\" finished. Resuming the main thread.`
+              : `Background task \"${params.description}\" failed. Resuming the main thread.`,
+          variant: input.state === "completed" ? "success" : "error",
+          duration: 5000,
+        })
+        yield* ops.loop({ sessionID: ctx.sessionID }).pipe(Effect.ignore)
+      })
+
+      if (background) {
+        const inject = Effect.fn("TaskTool.injectBackgroundResult")(function* (state: "completed" | "error", text: string) {
+          const message = yield* ops.prompt({
+            sessionID: ctx.sessionID,
+            noReply: true,
+            model: parentModel,
+            agent: ctx.agent,
+            parts: [
+              {
+                type: "text",
+                synthetic: true,
+                text: backgroundMessage({
+                  sessionID: nextSession.id,
+                  description: params.description,
+                  state,
+                  text,
+                }),
+              },
+            ],
+          })
+          yield* continueIfIdle({ userID: message.info.id, state })
+        })
+
+        ops.fork(
+          runTask().pipe(
+            Effect.matchCauseEffect({
+              onSuccess: (text) => inject("completed", text),
+              onFailure: (cause) =>
+                inject("error", errorText(Cause.squash(cause))).pipe(Effect.catchCause(() => Effect.void)),
+            }),
+            Effect.catchCause(() => Effect.void),
+            Effect.asVoid,
+          ),
+        )
+
+        return {
+          title: params.description,
+          metadata,
+          output: backgroundOutput(nextSession.id),
+        }
+      }
 
       function cancel() {
         ops.cancel(nextSession.id)
@@ -127,36 +262,11 @@ export const TaskTool = Tool.define(
         }),
         () =>
           Effect.gen(function* () {
-            const parts = yield* ops.resolvePromptParts(params.prompt)
-            const result = yield* ops.prompt({
-              messageID,
-              sessionID: nextSession.id,
-              model: {
-                modelID: model.modelID,
-                providerID: model.providerID,
-              },
-              agent: next.name,
-              tools: {
-                ...(canTodo ? {} : { todowrite: false }),
-                ...(canTask ? {} : { task: false }),
-                ...Object.fromEntries((cfg.experimental?.primary_tools ?? []).map((item) => [item, false])),
-              },
-              parts,
-            })
-
+            const text = yield* runTask()
             return {
               title: params.description,
-              metadata: {
-                sessionId: nextSession.id,
-                model,
-              },
-              output: [
-                `task_id: ${nextSession.id} (for resuming to continue this task if needed)`,
-                "",
-                "<task_result>",
-                result.parts.findLast((item) => item.type === "text")?.text ?? "",
-                "</task_result>",
-              ].join("\n"),
+              metadata,
+              output: output(nextSession.id, text),
             }
           }),
         () =>
diff --git a/packages/opencode/src/tool/task.txt b/packages/opencode/src/tool/task.txt
index fba8470d1b..5d26066a8c 100644
--- a/packages/opencode/src/tool/task.txt
+++ b/packages/opencode/src/tool/task.txt
@@ -14,11 +14,13 @@ When NOT to use the Task tool:
 
 Usage notes:
 1. Launch multiple agents concurrently whenever possible, to maximize performance; to do that, use a single message with multiple tool uses
-2. When the agent is done, it will return a single message back to you. The result returned by the agent is not visible to the user. To show the user the result, you should send a text message back to the user with a concise summary of the result. The output includes a task_id you can reuse later to continue the same subagent session.
-3. Each agent invocation starts with a fresh context unless you provide task_id to resume the same subagent session (which continues with its previous messages and tool outputs). When starting fresh, your prompt should contain a highly detailed task description for the agent to perform autonomously and you should specify exactly what information the agent should return back to you in its final and only message to you.
-4. The agent's outputs should generally be trusted
-5. Clearly tell the agent whether you expect it to write code or just to do research (search, file reads, web fetches, etc.), since it is not aware of the user's intent. Tell it how to verify its work if possible (e.g., relevant test commands).
-6. If the agent description mentions that it should be used proactively, then you should try your best to use it without the user having to ask for it first. Use your judgement.
+2. By default, task waits for completion and returns the result immediately, along with a task_id you can reuse later to continue the same subagent session.
+3. Set background=true to launch asynchronously. In background mode, continue your current work without waiting.
+4. For background runs, use task_status(task_id=..., wait=false) to poll, or wait=true to block until done (optionally with timeout_ms).
+5. Each agent invocation starts with a fresh context unless you provide task_id to resume the same subagent session (which continues with its previous messages and tool outputs). When starting fresh, your prompt should contain a highly detailed task description for the agent to perform autonomously and you should specify exactly what information the agent should return back to you in its final and only message to you.
+6. The agent's outputs should generally be trusted
+7. Clearly tell the agent whether you expect it to write code or just to do research (search, file reads, web fetches, etc.), since it is not aware of the user's intent. Tell it how to verify its work if possible (e.g., relevant test commands).
+8. If the agent description mentions that it should be used proactively, then you should try your best to use it without the user having to ask for it first. Use your judgement.
 
 Example usage (NOTE: The agents below are fictional examples for illustration only - use the actual agents listed above):
 
diff --git a/packages/opencode/src/tool/task_status.ts b/packages/opencode/src/tool/task_status.ts
new file mode 100644
index 0000000000..60d5218a38
--- /dev/null
+++ b/packages/opencode/src/tool/task_status.ts
@@ -0,0 +1,145 @@
+import * as Tool from "./tool"
+import DESCRIPTION from "./task_status.txt"
+import { Session } from "../session"
+import { SessionID } from "../session/schema"
+import { MessageV2 } from "../session/message-v2"
+import { SessionStatus } from "../session/status"
+import { PositiveInt } from "@/util/schema"
+import { Effect, Option, Schema } from "effect"
+
+const DEFAULT_TIMEOUT = 60_000
+const POLL_MS = 300
+
+const Parameters = Schema.Struct({
+  task_id: SessionID.annotate({ description: "The task_id returned by the task tool" }),
+  wait: Schema.optional(Schema.Boolean).annotate({ description: "When true, wait until the task reaches a terminal state or timeout" }),
+  timeout_ms: Schema.optional(PositiveInt).annotate({
+    description: "Maximum milliseconds to wait when wait=true (default: 60000)",
+  }),
+})
+
+type State = "running" | "completed" | "error"
+type InspectResult = { state: State; text: string }
+
+function format(input: { taskID: SessionID; state: State; text: string }) {
+  return [`task_id: ${input.taskID}`, `state: ${input.state}`, "", "<task_result>", input.text, "</task_result>"].join(
+    "\n",
+  )
+}
+
+function errorText(error: NonNullable<MessageV2.Assistant["error"]>) {
+  const data = Reflect.get(error, "data")
+  const message = data && typeof data === "object" ? Reflect.get(data, "message") : undefined
+  if (typeof message === "string" && message) return message
+  return error.name
+}
+
+export const TaskStatusTool = Tool.define(
+  "task_status",
+  Effect.gen(function* () {
+    const sessions = yield* Session.Service
+    const status = yield* SessionStatus.Service
+
+    const inspect: (taskID: SessionID) => Effect.Effect<InspectResult> = Effect.fn("TaskStatusTool.inspect")(function* (
+      taskID: SessionID,
+    ) {
+      const current = yield* status.get(taskID)
+      if (current.type === "busy" || current.type === "retry") {
+        return {
+          state: "running" as const,
+          text: current.type === "retry" ? `Task is retrying: ${current.message}` : "Task is still running.",
+        }
+      }
+
+      const latestAssistant = yield* sessions.findMessage(taskID, (item) => item.info.role === "assistant")
+      if (Option.isNone(latestAssistant)) {
+        return {
+          state: "running" as const,
+          text: "Task has started but has not produced output yet.",
+        }
+      }
+      if (latestAssistant.value.info.role !== "assistant") {
+        return {
+          state: "running" as const,
+          text: "Task has started but has not produced output yet.",
+        }
+      }
+
+      const latestUser = yield* sessions.findMessage(taskID, (item) => item.info.role === "user")
+      if (Option.isSome(latestUser) && latestUser.value.info.role === "user" && latestUser.value.info.id > latestAssistant.value.info.id) {
+        return {
+          state: "running" as const,
+          text: "Task is starting.",
+        }
+      }
+
+      const text = latestAssistant.value.parts.findLast((part) => part.type === "text")?.text ?? ""
+      if (latestAssistant.value.info.error) {
+        return {
+          state: "error" as const,
+          text: text || errorText(latestAssistant.value.info.error),
+        }
+      }
+
+      const done =
+        !!latestAssistant.value.info.finish && !["tool-calls", "unknown"].includes(latestAssistant.value.info.finish)
+      if (done) {
+        return {
+          state: "completed" as const,
+          text,
+        }
+      }
+
+      return {
+        state: "running" as const,
+        text: text || "Task is still running.",
+      }
+    })
+
+    const waitForTerminal: (taskID: SessionID, timeout: number) => Effect.Effect<{ result: InspectResult; timedOut: boolean }> =
+      Effect.fn("TaskStatusTool.waitForTerminal")(function* (taskID: SessionID, timeout: number) {
+        const result = yield* inspect(taskID)
+        if (result.state !== "running") return { result, timedOut: false }
+        if (timeout <= 0) return { result, timedOut: true }
+        const sleep = Math.min(POLL_MS, timeout)
+        yield* Effect.sleep(`${sleep} millis`)
+        return yield* waitForTerminal(taskID, timeout - sleep)
+      })
+
+    const run = Effect.fn("TaskStatusTool.execute")(function* (
+      params: Schema.Schema.Type<typeof Parameters>,
+      _ctx: Tool.Context,
+    ) {
+      yield* sessions.get(params.task_id)
+
+      const waited =
+        params.wait === true
+          ? yield* waitForTerminal(params.task_id, params.timeout_ms ?? DEFAULT_TIMEOUT)
+          : { result: yield* inspect(params.task_id), timedOut: false }
+
+      const outputText = waited.timedOut
+        ? `Timed out after ${params.timeout_ms ?? DEFAULT_TIMEOUT}ms while waiting for task completion.`
+        : waited.result.text
+
+      return {
+        title: "Task status",
+        metadata: {
+          task_id: params.task_id,
+          state: waited.result.state,
+          timed_out: waited.timedOut,
+        },
+        output: format({
+          taskID: params.task_id,
+          state: waited.result.state,
+          text: outputText,
+        }),
+      }
+    })
+
+    return {
+      description: DESCRIPTION,
+      parameters: Parameters,
+      execute: (params: Schema.Schema.Type<typeof Parameters>, ctx: Tool.Context) => run(params, ctx).pipe(Effect.orDie),
+    }
+  }),
+)
diff --git a/packages/opencode/src/tool/task_status.txt b/packages/opencode/src/tool/task_status.txt
new file mode 100644
index 0000000000..3f8af0d609
--- /dev/null
+++ b/packages/opencode/src/tool/task_status.txt
@@ -0,0 +1,13 @@
+Poll the status of a subagent task launched with the task tool.
+
+Use this to check background tasks started with `task(background=true)`.
+
+Parameters:
+- `task_id` (required): the task session id returned by the task tool
+- `wait` (optional): when true, wait for completion
+- `timeout_ms` (optional): max wait duration in milliseconds when `wait=true`
+
+Returns compact, parseable output:
+- `task_id`
+- `state` (`running`, `completed`, or `error`)
+- `<task_result>...</task_result>` containing final output, error summary, or current progress text
diff --git a/packages/opencode/test/tool/task.test.ts b/packages/opencode/test/tool/task.test.ts
index b94dd52086..95ee49a0c2 100644
--- a/packages/opencode/test/tool/task.test.ts
+++ b/packages/opencode/test/tool/task.test.ts
@@ -1,13 +1,15 @@
 import { afterEach, describe, expect } from "bun:test"
 import { Effect, Layer } from "effect"
 import { Agent } from "../../src/agent/agent"
+import { Bus } from "../../src/bus"
 import { Config } from "../../src/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 type { SessionPrompt } from "../../src/session/prompt"
-import { MessageID, PartID } from "../../src/session/schema"
+import { MessageID, PartID, SessionID } from "../../src/session/schema"
+import { SessionStatus } from "../../src/session/status"
 import { ModelID, ProviderID } from "../../src/provider/schema"
 import { TaskTool, type TaskPromptOps } from "../../src/tool/task"
 import { Truncate } from "../../src/tool"
@@ -27,9 +29,11 @@ const ref = {
 const it = testEffect(
   Layer.mergeAll(
     Agent.defaultLayer,
+    Bus.defaultLayer,
     Config.defaultLayer,
     CrossSpawnSpawner.defaultLayer,
     Session.defaultLayer,
+    SessionStatus.defaultLayer,
     Truncate.defaultLayer,
     ToolRegistry.defaultLayer,
   ),
@@ -64,15 +68,59 @@ const seed = Effect.fn("TaskToolTest.seed")(function* (title = "Pinned") {
   return { chat, assistant }
 })
 
-function stubOps(opts?: { onPrompt?: (input: SessionPrompt.PromptInput) => void; text?: string }): TaskPromptOps {
+function stubOps(session: Session.Interface, opts?: { onPrompt?: (input: SessionPrompt.PromptInput) => void; text?: string }): TaskPromptOps {
   return {
     cancel() {},
     resolvePromptParts: (template) => Effect.succeed([{ type: "text" as const, text: template }]),
     prompt: (input) =>
-      Effect.sync(() => {
+      Effect.gen(function* () {
         opts?.onPrompt?.(input)
-        return reply(input, opts?.text ?? "done")
+        const userID = input.messageID ?? MessageID.ascending()
+        const user: MessageV2.User = {
+          id: userID,
+          role: "user",
+          sessionID: input.sessionID,
+          agent: input.agent ?? "build",
+          model: input.model ?? ref,
+          tools: input.tools,
+          time: { created: Date.now() },
+        }
+        yield* session.updateMessage(user)
+
+        const parts = input.parts.map((part) => ({
+          ...part,
+          id: part.id ?? PartID.ascending(),
+          messageID: user.id,
+          sessionID: input.sessionID,
+        }))
+        yield* Effect.forEach(parts, (part) => session.updatePart(part), { discard: true })
+
+        if (input.noReply) {
+          return {
+            info: user,
+            parts,
+          }
+        }
+
+        const result = reply({ ...input, messageID: user.id }, opts?.text ?? "done")
+        yield* session.updateMessage(result.info)
+        yield* Effect.forEach(result.parts, (part) => session.updatePart(part), { discard: true })
+        return result
       }),
+    loop: (input) =>
+      Effect.sync(() =>
+        reply(
+          {
+            sessionID: input.sessionID,
+            messageID: MessageID.ascending(),
+            agent: "build",
+            model: ref,
+            parts: [],
+          },
+          opts?.text ?? "done",
+        ),
+      ),
+    fork() {},
   }
 }
 
@@ -195,7 +243,7 @@ describe("tool.task", () => {
         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(sessions, { text: "resumed", onPrompt: (input) => (seen = input) })
 
         const result = yield* def.execute(
           {
@@ -229,11 +277,12 @@ describe("tool.task", () => {
   it.live("execute asks by default and skips checks when bypassed", () =>
     provideTmpdirInstance(() =>
       Effect.gen(function* () {
+        const sessions = yield* Session.Service
         const { chat, assistant } = yield* seed()
         const tool = yield* TaskTool
         const def = yield* tool.init()
         const calls: unknown[] = []
-        const promptOps = stubOps()
+        const promptOps = stubOps(sessions)
 
         const exec = (extra?: Record<string, any>) =>
           def.execute(
@@ -282,15 +331,15 @@ describe("tool.task", () => {
         const tool = yield* TaskTool
         const def = yield* tool.init()
         let seen: SessionPrompt.PromptInput | undefined
-        const promptOps = stubOps({ text: "created", onPrompt: (input) => (seen = input) })
+        const promptOps = stubOps(sessions, { 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",
-          },
+              prompt: "look into the cache key path",
+              subagent_type: "general",
+              task_id: SessionID.make("ses_missing"),
+            },
           {
             sessionID: chat.id,
             messageID: assistant.id,
@@ -322,7 +371,7 @@ describe("tool.task", () => {
           const tool = yield* TaskTool
           const def = yield* tool.init()
           let seen: SessionPrompt.PromptInput | undefined
-          const promptOps = stubOps({ onPrompt: (input) => (seen = input) })
+          const promptOps = stubOps(sessions, { onPrompt: (input) => (seen = input) })
 
           const result = yield* def.execute(
             {
@@ -384,4 +433,116 @@ describe("tool.task", () => {
       },
     ),
   )
+
+  it.live("execute launches background tasks without waiting for completion", () =>
+    provideTmpdirInstance(() =>
+      Effect.gen(function* () {
+        const sessions = yield* Session.Service
+        const { chat, assistant } = yield* seed()
+        const tool = yield* TaskTool
+        const def = yield* tool.init()
+        const forks: Effect.Effect<void, never, never>[] = []
+
+        const result = yield* def.execute(
+          {
+            description: "inspect bug",
+            prompt: "look into the cache key path",
+            subagent_type: "general",
+            background: true,
+          },
+          {
+            sessionID: chat.id,
+            messageID: assistant.id,
+            agent: "build",
+            abort: new AbortController().signal,
+            extra: {
+              promptOps: {
+                ...stubOps(sessions),
+                fork(effect) {
+                  forks.push(effect)
+                },
+              } satisfies TaskPromptOps,
+            },
+            messages: [],
+            metadata: () => Effect.void,
+            ask: () => Effect.void,
+          },
+        )
+
+        expect(result.metadata.sessionId).toBeDefined()
+        expect(result.metadata.background).toBe(true)
+        expect(result.output).toContain(`task_id: ${result.metadata.sessionId}`)
+        expect(result.output).toContain("state: running")
+        expect(forks).toHaveLength(1)
+      }),
+    ),
+  )
+
+  it.live("background tasks inject completion into the parent session and resume when idle", () =>
+    provideTmpdirInstance(() =>
+      Effect.gen(function* () {
+        const sessions = yield* Session.Service
+        const { chat, assistant } = yield* seed()
+        const tool = yield* TaskTool
+        const def = yield* tool.init()
+        const forks: Effect.Effect<void, never, never>[] = []
+        const loops: string[] = []
+
+        const result = yield* def.execute(
+          {
+            description: "inspect bug",
+            prompt: "look into the cache key path",
+            subagent_type: "general",
+            background: true,
+          },
+          {
+            sessionID: chat.id,
+            messageID: assistant.id,
+            agent: "build",
+            abort: new AbortController().signal,
+            extra: {
+              promptOps: {
+                ...stubOps(sessions, { text: "background done" }),
+                loop(input) {
+                  loops.push(input.sessionID)
+                  return Effect.sync(() =>
+                    reply(
+                      {
+                        sessionID: input.sessionID,
+                        messageID: MessageID.ascending(),
+                        agent: "build",
+                        model: ref,
+                        parts: [],
+                      },
+                      "looped",
+                    ),
+                  )
+                },
+                fork(effect) {
+                  forks.push(effect)
+                },
+              } satisfies TaskPromptOps,
+            },
+            messages: [],
+            metadata: () => Effect.void,
+            ask: () => Effect.void,
+          },
+        )
+
+        yield* forks[0]!
+
+        const parent = yield* sessions.findMessage(chat.id, (msg) => msg.info.role === "user")
+        expect(parent._tag).toBe("Some")
+        if (parent._tag !== "Some") return
+        expect(parent.value.parts.find((part) => part.type === "text")?.text).toContain("Background task completed")
+        expect(parent.value.parts.find((part) => part.type === "text")?.text).toContain("background done")
+        expect(loops).toEqual([chat.id])
+
+        const child = yield* sessions.findMessage(result.metadata.sessionId, (msg) => msg.info.role === "assistant")
+        expect(child._tag).toBe("Some")
+        if (child._tag !== "Some") return
+        expect(child.value.parts.find((part) => part.type === "text")?.text).toBe("background done")
+      }),
+    ),
+  )
 })
diff --git a/packages/opencode/test/tool/task_status.test.ts b/packages/opencode/test/tool/task_status.test.ts
new file mode 100644
index 0000000000..6081f6a923
--- /dev/null
+++ b/packages/opencode/test/tool/task_status.test.ts
@@ -0,0 +1,278 @@
+import { afterEach, describe, expect } from "bun:test"
+import { Effect, Layer, Scope } from "effect"
+import { Agent } from "../../src/agent/agent"
+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 { MessageID, PartID } from "../../src/session/schema"
+import { SessionStatus } from "../../src/session/status"
+import { TaskStatusTool } from "../../src/tool/task_status"
+import { Truncate } from "../../src/tool"
+import { ModelID, ProviderID } from "../../src/provider/schema"
+import { provideTmpdirInstance } from "../fixture/fixture"
+import { testEffect } from "../lib/effect"
+
+afterEach(async () => {
+  await Instance.disposeAll()
+})
+
+const ref = {
+  providerID: ProviderID.make("test"),
+  modelID: ModelID.make("test-model"),
+}
+
+const it = testEffect(
+  Layer.mergeAll(
+    Agent.defaultLayer,
+    CrossSpawnSpawner.defaultLayer,
+    Session.defaultLayer,
+    SessionStatus.defaultLayer,
+    Truncate.defaultLayer,
+  ),
+)
+
+const seedUser = Effect.fn("TaskStatusToolTest.seedUser")(function* (sessionID: Session.Info["id"]) {
+  const session = yield* Session.Service
+  return yield* session.updateMessage({
+    id: MessageID.ascending(),
+    role: "user",
+    sessionID,
+    agent: "build",
+    model: ref,
+    time: { created: Date.now() },
+  })
+})
+
+const seedAssistant = Effect.fn("TaskStatusToolTest.seedAssistant")(function* (input: {
+  sessionID: Session.Info["id"]
+  text: string
+  error?: string
+}) {
+  const session = yield* Session.Service
+  const user = yield* seedUser(input.sessionID)
+  const message = yield* session.updateMessage({
+    id: MessageID.ascending(),
+    role: "assistant",
+    parentID: user.id,
+    sessionID: input.sessionID,
+    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(), completed: Date.now() },
+    finish: "stop",
+    ...(input.error
+      ? {
+          error: new MessageV2.APIError({
+            message: input.error,
+            isRetryable: false,
+          }).toObject(),
+        }
+      : {}),
+  })
+
+  yield* session.updatePart({
+    id: PartID.ascending(),
+    messageID: message.id,
+    sessionID: input.sessionID,
+    type: "text",
+    text: input.text,
+  })
+})
+
+describe("tool.task_status", () => {
+  it.live("returns running while session status is busy", () =>
+    provideTmpdirInstance(() =>
+      Effect.gen(function* () {
+        const sessions = yield* Session.Service
+        const status = yield* SessionStatus.Service
+        const tool = yield* TaskStatusTool
+        const def = yield* tool.init()
+        const chat = yield* sessions.create({})
+
+        yield* status.set(chat.id, { type: "busy" })
+        const result = yield* def.execute(
+          { task_id: chat.id },
+          {
+            sessionID: chat.id,
+            messageID: MessageID.ascending(),
+            agent: "build",
+            abort: new AbortController().signal,
+            messages: [],
+            metadata: () => Effect.void,
+            ask: () => Effect.void,
+          },
+        )
+
+        expect(result.output).toContain("state: running")
+      }),
+    ),
+  )
+
+  it.live("returns completed with final task output", () =>
+    provideTmpdirInstance(() =>
+      Effect.gen(function* () {
+        const sessions = yield* Session.Service
+        const tool = yield* TaskStatusTool
+        const def = yield* tool.init()
+        const chat = yield* sessions.create({})
+
+        yield* seedAssistant({ sessionID: chat.id, text: "all done" })
+
+        const result = yield* def.execute(
+          { task_id: chat.id },
+          {
+            sessionID: chat.id,
+            messageID: MessageID.ascending(),
+            agent: "build",
+            abort: new AbortController().signal,
+            messages: [],
+            metadata: () => Effect.void,
+            ask: () => Effect.void,
+          },
+        )
+
+        expect(result.output).toContain("state: completed")
+        expect(result.output).toContain("all done")
+      }),
+    ),
+  )
+
+  it.live("wait=true blocks until terminal status", () =>
+    provideTmpdirInstance(() =>
+      Effect.gen(function* () {
+        const sessions = yield* Session.Service
+        const status = yield* SessionStatus.Service
+        const tool = yield* TaskStatusTool
+        const def = yield* tool.init()
+        const chat = yield* sessions.create({})
+        const scope = yield* Scope.Scope
+
+        yield* status.set(chat.id, { type: "busy" })
+        yield* Effect.gen(function* () {
+          yield* Effect.sleep("150 millis")
+          yield* status.set(chat.id, { type: "idle" })
+          yield* seedAssistant({ sessionID: chat.id, text: "finished later" })
+        }).pipe(Effect.forkIn(scope))
+
+        const result = yield* def.execute(
+          {
+            task_id: chat.id,
+            wait: true,
+            timeout_ms: 4_000,
+          },
+          {
+            sessionID: chat.id,
+            messageID: MessageID.ascending(),
+            agent: "build",
+            abort: new AbortController().signal,
+            messages: [],
+            metadata: () => Effect.void,
+            ask: () => Effect.void,
+          },
+        )
+
+        expect(result.output).toContain("state: completed")
+        expect(result.output).toContain("finished later")
+      }),
+    ),
+  )
+
+  it.live("returns error when child run fails", () =>
+    provideTmpdirInstance(() =>
+      Effect.gen(function* () {
+        const sessions = yield* Session.Service
+        const tool = yield* TaskStatusTool
+        const def = yield* tool.init()
+        const chat = yield* sessions.create({})
+
+        yield* seedAssistant({ sessionID: chat.id, text: "", error: "child failed" })
+
+        const result = yield* def.execute(
+          { task_id: chat.id },
+          {
+            sessionID: chat.id,
+            messageID: MessageID.ascending(),
+            agent: "build",
+            abort: new AbortController().signal,
+            messages: [],
+            metadata: () => Effect.void,
+            ask: () => Effect.void,
+          },
+        )
+
+        expect(result.output).toContain("state: error")
+        expect(result.output).toContain("child failed")
+        expect(result.metadata.state).toBe("error")
+      }),
+    ),
+  )
+
+  it.live("wait=true times out with timed_out metadata", () =>
+    provideTmpdirInstance(() =>
+      Effect.gen(function* () {
+        const sessions = yield* Session.Service
+        const status = yield* SessionStatus.Service
+        const tool = yield* TaskStatusTool
+        const def = yield* tool.init()
+        const chat = yield* sessions.create({})
+
+        yield* status.set(chat.id, { type: "busy" })
+        const result = yield* def.execute(
+          {
+            task_id: chat.id,
+            wait: true,
+            timeout_ms: 80,
+          },
+          {
+            sessionID: chat.id,
+            messageID: MessageID.ascending(),
+            agent: "build",
+            abort: new AbortController().signal,
+            messages: [],
+            metadata: () => Effect.void,
+            ask: () => Effect.void,
+          },
+        )
+
+        expect(result.output).toContain("Timed out after 80ms")
+        expect(result.metadata.timed_out).toBe(true)
+        expect(result.metadata.state).toBe("running")
+      }),
+    ),
+  )
+
+  it.live("returns running for resumed task with a newer user turn", () =>
+    provideTmpdirInstance(() =>
+      Effect.gen(function* () {
+        const sessions = yield* Session.Service
+        const tool = yield* TaskStatusTool
+        const def = yield* tool.init()
+        const chat = yield* sessions.create({})
+
+        yield* seedAssistant({ sessionID: chat.id, text: "old done" })
+        yield* seedUser(chat.id)
+
+        const result = yield* def.execute(
+          { task_id: chat.id },
+          {
+            sessionID: chat.id,
+            messageID: MessageID.ascending(),
+            agent: "build",
+            abort: new AbortController().signal,
+            messages: [],
+            metadata: () => Effect.void,
+            ask: () => Effect.void,
+          },
+        )
+
+        expect(result.output).toContain("state: running")
+        expect(result.output).toContain("Task is starting.")
+      }),
+    ),
+  )
+})

From 7970130720a1acf4a405b5bf587cb880e3273713 Mon Sep 17 00:00:00 2001
From: Shoubhit Dash <shoubhit2005@gmail.com>
Date: Fri, 24 Apr 2026 20:08:32 +0530
Subject: [PATCH 2/6] fix(ui): label background task cards

---
 packages/opencode/src/cli/cmd/tui/routes/session/index.tsx | 3 ++-
 packages/ui/src/components/message-part.tsx                | 7 ++++---
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx b/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
index c04e58acec..b6cde459e9 100644
--- a/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
+++ b/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
@@ -2000,7 +2000,8 @@ function Task(props: ToolProps<typeof TaskTool>) {
 
   const content = createMemo(() => {
     if (!props.input.description) return ""
-    let content = [`${Locale.titlecase(props.input.subagent_type ?? "General")} Task — ${props.input.description}`]
+    const description = props.metadata.background === true ? `${props.input.description} (background)` : props.input.description
+    let content = [`${Locale.titlecase(props.input.subagent_type ?? "General")} Task — ${description}`]
 
     if (isRunning() && tools().length > 0) {
       // content[0] += ` · ${tools().length} toolcalls`
diff --git a/packages/ui/src/components/message-part.tsx b/packages/ui/src/components/message-part.tsx
index 9c0c90c000..3694b204fb 100644
--- a/packages/ui/src/components/message-part.tsx
+++ b/packages/ui/src/components/message-part.tsx
@@ -1751,9 +1751,10 @@ ToolRegistry.register({
     const title = createMemo(() => agent().name ?? i18n.t("ui.tool.agent.default"))
     const tone = createMemo(() => agent().color)
     const subtitle = createMemo(() => {
-      const value = props.input.description
-      if (typeof value === "string" && value) return value
-      return childSessionId()
+      const value = typeof props.input.description === "string" && props.input.description ? props.input.description : childSessionId()
+      if (!value) return value
+      if (props.metadata.background === true) return `${value} (background)`
+      return value
     })
     const running = createMemo(() => props.status === "pending" || props.status === "running")
 

From ecde8ab3633b10919b5fa67938282d7e806b121d Mon Sep 17 00:00:00 2001
From: Shoubhit Dash <shoubhit2005@gmail.com>
Date: Fri, 24 Apr 2026 20:20:04 +0530
Subject: [PATCH 3/6] test(task): update parameter schema snapshot

---
 .../test/tool/__snapshots__/parameters.test.ts.snap |  5 +++++
 packages/opencode/test/tool/parameters.test.ts      | 13 +++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/packages/opencode/test/tool/__snapshots__/parameters.test.ts.snap b/packages/opencode/test/tool/__snapshots__/parameters.test.ts.snap
index eb3fe6cce4..ffb1b9f55f 100644
--- a/packages/opencode/test/tool/__snapshots__/parameters.test.ts.snap
+++ b/packages/opencode/test/tool/__snapshots__/parameters.test.ts.snap
@@ -334,6 +334,10 @@ exports[`tool parameters JSON Schema (wire shape) task 1`] = `
 {
   "$schema": "https://json-schema.org/draft/2020-12/schema",
   "properties": {
+    "background": {
+      "description": "When true, launch the subagent in the background and return immediately",
+      "type": "boolean",
+    },
     "command": {
       "description": "The command that triggered this task",
       "type": "string",
@@ -352,6 +356,7 @@ exports[`tool parameters JSON Schema (wire shape) task 1`] = `
     },
     "task_id": {
       "description": "This should only be set if you mean to resume a previous task (you can pass a prior task_id and the task will continue the same subagent session as before instead of creating a fresh one)",
+      "pattern": "^ses.*",
       "type": "string",
     },
   },
diff --git a/packages/opencode/test/tool/parameters.test.ts b/packages/opencode/test/tool/parameters.test.ts
index 8ea008a457..487e6faa17 100644
--- a/packages/opencode/test/tool/parameters.test.ts
+++ b/packages/opencode/test/tool/parameters.test.ts
@@ -220,6 +220,19 @@ describe("tool parameters", () => {
       const parsed = parse(Task, { description: "d", prompt: "p", subagent_type: "general" })
       expect(parsed.subagent_type).toBe("general")
     })
+    test("accepts optional task_id + command + background", () => {
+      const parsed = parse(Task, {
+        description: "d",
+        prompt: "p",
+        subagent_type: "general",
+        task_id: "ses_test",
+        command: "/cmd",
+        background: true,
+      })
+      expect(parsed.task_id).toBe("ses_test")
+      expect(parsed.command).toBe("/cmd")
+      expect(parsed.background).toBe(true)
+    })
     test("rejects missing prompt", () => {
       expect(accepts(Task, { description: "d", subagent_type: "general" })).toBe(false)
     })

From 1357bb984f8fe70222d468a6ddc03340336ee4c5 Mon Sep 17 00:00:00 2001
From: Shoubhit Dash <shoubhit2005@gmail.com>
Date: Fri, 24 Apr 2026 20:20:04 +0530
Subject: [PATCH 4/6] style: fix background task formatting

---
 .../src/cli/cmd/tui/routes/session/index.tsx       |  3 ++-
 packages/opencode/src/tool/registry.ts             |  6 +++---
 packages/opencode/src/tool/task_status.ts          | 14 +++++++++++---
 packages/opencode/test/tool/task.test.ts           |  8 ++++----
 packages/ui/src/components/message-part.tsx        |  3 ++-
 5 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx b/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
index b6cde459e9..50e39c7c3a 100644
--- a/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
+++ b/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
@@ -2000,7 +2000,8 @@ function Task(props: ToolProps<typeof TaskTool>) {
 
   const content = createMemo(() => {
     if (!props.input.description) return ""
-    const description = props.metadata.background === true ? `${props.input.description} (background)` : props.input.description
+    const description =
+      props.metadata.background === true ? `${props.input.description} (background)` : props.input.description
     let content = [`${Locale.titlecase(props.input.subagent_type ?? "General")} Task — ${description}`]
 
     if (isRunning() && tools().length > 0) {
diff --git a/packages/opencode/src/tool/registry.ts b/packages/opencode/src/tool/registry.ts
index eb0c75c7ac..64c38ccb4f 100644
--- a/packages/opencode/src/tool/registry.ts
+++ b/packages/opencode/src/tool/registry.ts
@@ -80,9 +80,9 @@ export const layer: Layer.Layer<
   | Todo.Service
   | Agent.Service
   | Skill.Service
-   | Session.Service
-   | SessionStatus.Service
-   | Provider.Service
+  | Session.Service
+  | SessionStatus.Service
+  | Provider.Service
   | LSP.Service
   | Instruction.Service
   | AppFileSystem.Service
diff --git a/packages/opencode/src/tool/task_status.ts b/packages/opencode/src/tool/task_status.ts
index 60d5218a38..db7960b485 100644
--- a/packages/opencode/src/tool/task_status.ts
+++ b/packages/opencode/src/tool/task_status.ts
@@ -66,7 +66,11 @@ export const TaskStatusTool = Tool.define(
       }
 
       const latestUser = yield* sessions.findMessage(taskID, (item) => item.info.role === "user")
-      if (Option.isSome(latestUser) && latestUser.value.info.role === "user" && latestUser.value.info.id > latestAssistant.value.info.id) {
+      if (
+        Option.isSome(latestUser) &&
+        latestUser.value.info.role === "user" &&
+        latestUser.value.info.id > latestAssistant.value.info.id
+      ) {
         return {
           state: "running" as const,
           text: "Task is starting.",
@@ -96,8 +100,12 @@ export const TaskStatusTool = Tool.define(
       }
     })
 
-    const waitForTerminal: (taskID: SessionID, timeout: number) => Effect.Effect<{ result: InspectResult; timedOut: boolean }> =
-      Effect.fn("TaskStatusTool.waitForTerminal")(function* (taskID: SessionID, timeout: number) {
+    const waitForTerminal: (
+      taskID: SessionID,
+      timeout: number,
+    ) => Effect.Effect<{ result: InspectResult; timedOut: boolean }> = Effect.fn(
+      "TaskStatusTool.waitForTerminal",
+    )(function* (taskID: SessionID, timeout: number) {
         const result = yield* inspect(taskID)
         if (result.state !== "running") return { result, timedOut: false }
         if (timeout <= 0) return { result, timedOut: true }
diff --git a/packages/opencode/test/tool/task.test.ts b/packages/opencode/test/tool/task.test.ts
index 95ee49a0c2..a5724630ec 100644
--- a/packages/opencode/test/tool/task.test.ts
+++ b/packages/opencode/test/tool/task.test.ts
@@ -336,10 +336,10 @@ describe("tool.task", () => {
         const result = yield* def.execute(
           {
             description: "inspect bug",
-              prompt: "look into the cache key path",
-              subagent_type: "general",
-              task_id: SessionID.make("ses_missing"),
-            },
+            prompt: "look into the cache key path",
+            subagent_type: "general",
+            task_id: SessionID.make("ses_missing"),
+          },
           {
             sessionID: chat.id,
             messageID: assistant.id,
diff --git a/packages/ui/src/components/message-part.tsx b/packages/ui/src/components/message-part.tsx
index 3694b204fb..eb90b4d9e6 100644
--- a/packages/ui/src/components/message-part.tsx
+++ b/packages/ui/src/components/message-part.tsx
@@ -1751,7 +1751,8 @@ ToolRegistry.register({
     const title = createMemo(() => agent().name ?? i18n.t("ui.tool.agent.default"))
     const tone = createMemo(() => agent().color)
     const subtitle = createMemo(() => {
-      const value = typeof props.input.description === "string" && props.input.description ? props.input.description : childSessionId()
+      const value =
+        typeof props.input.description === "string" && props.input.description ? props.input.description : childSessionId()
       if (!value) return value
       if (props.metadata.background === true) return `${value} (background)`
       return value

From 3f4b9d9ef4bf8c8450015c9cc3a7aaa2437058cc Mon Sep 17 00:00:00 2001
From: Shoubhit Dash <shoubhit2005@gmail.com>
Date: Fri, 24 Apr 2026 20:21:02 +0530
Subject: [PATCH 5/6] test(task): use branded session id in schema test

---
 packages/opencode/test/tool/parameters.test.ts | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/packages/opencode/test/tool/parameters.test.ts b/packages/opencode/test/tool/parameters.test.ts
index 487e6faa17..52d7f44ee3 100644
--- a/packages/opencode/test/tool/parameters.test.ts
+++ b/packages/opencode/test/tool/parameters.test.ts
@@ -26,6 +26,7 @@ import { Parameters as Todo } from "../../src/tool/todo"
 import { Parameters as WebFetch } from "../../src/tool/webfetch"
 import { Parameters as WebSearch } from "../../src/tool/websearch"
 import { Parameters as Write } from "../../src/tool/write"
+import { SessionID } from "../../src/session/schema"
 
 const parse = <S extends Schema.Decoder<unknown>>(schema: S, input: unknown): S["Type"] =>
   Schema.decodeUnknownSync(schema)(input)
@@ -225,11 +226,11 @@ describe("tool parameters", () => {
         description: "d",
         prompt: "p",
         subagent_type: "general",
-        task_id: "ses_test",
+        task_id: SessionID.make("ses_test"),
         command: "/cmd",
         background: true,
       })
-      expect(parsed.task_id).toBe("ses_test")
+      expect(parsed.task_id).toBe(SessionID.make("ses_test"))
       expect(parsed.command).toBe("/cmd")
       expect(parsed.background).toBe(true)
     })

From 601fe03a3a571b8da3a9aabc52ee869624fe6e61 Mon Sep 17 00:00:00 2001
From: Shoubhit Dash <shoubhit2005@gmail.com>
Date: Fri, 24 Apr 2026 20:30:53 +0530
Subject: [PATCH 6/6] refactor(task): simplify effect wrappers

---
 packages/opencode/src/tool/task.ts        | 12 +++++-------
 packages/opencode/src/tool/task_status.ts | 13 ++++++-------
 2 files changed, 11 insertions(+), 14 deletions(-)

diff --git a/packages/opencode/src/tool/task.ts b/packages/opencode/src/tool/task.ts
index 2bc58cdbb4..61b3294be5 100644
--- a/packages/opencode/src/tool/task.ts
+++ b/packages/opencode/src/tool/task.ts
@@ -81,10 +81,9 @@ export const TaskTool = Tool.define(
     const sessions = yield* Session.Service
     const status = yield* SessionStatus.Service
 
-    const run = Effect.fn("TaskTool.execute")(function* (
-      params: Schema.Schema.Type<typeof Parameters>,
-      ctx: Tool.Context,
-    ) {
+    const run = Effect.fn(
+      "TaskTool.execute",
+    )(function* (params: Schema.Schema.Type<typeof Parameters>, ctx: Tool.Context) {
       const cfg = yield* config.get()
 
       if (!ctx.extra?.bypassAgentCheck) {
@@ -274,13 +273,12 @@ export const TaskTool = Tool.define(
             ctx.abort.removeEventListener("abort", cancel)
           }),
       )
-    })
+    }, Effect.orDie)
 
     return {
       description: DESCRIPTION,
       parameters: Parameters,
-      execute: (params: Schema.Schema.Type<typeof Parameters>, ctx: Tool.Context) =>
-        run(params, ctx).pipe(Effect.orDie),
+      execute: run,
     }
   }),
 )
diff --git a/packages/opencode/src/tool/task_status.ts b/packages/opencode/src/tool/task_status.ts
index db7960b485..eba29576b3 100644
--- a/packages/opencode/src/tool/task_status.ts
+++ b/packages/opencode/src/tool/task_status.ts
@@ -110,14 +110,13 @@ export const TaskStatusTool = Tool.define(
         if (result.state !== "running") return { result, timedOut: false }
         if (timeout <= 0) return { result, timedOut: true }
         const sleep = Math.min(POLL_MS, timeout)
-        yield* Effect.sleep(`${sleep} millis`)
+        yield* Effect.sleep(sleep)
         return yield* waitForTerminal(taskID, timeout - sleep)
       })
 
-    const run = Effect.fn("TaskStatusTool.execute")(function* (
-      params: Schema.Schema.Type<typeof Parameters>,
-      _ctx: Tool.Context,
-    ) {
+    const run = Effect.fn(
+      "TaskStatusTool.execute",
+    )(function* (params: Schema.Schema.Type<typeof Parameters>, _ctx: Tool.Context) {
       yield* sessions.get(params.task_id)
 
       const waited =
@@ -142,12 +141,12 @@ export const TaskStatusTool = Tool.define(
           text: outputText,
         }),
       }
-    })
+    }, Effect.orDie)
 
     return {
       description: DESCRIPTION,
       parameters: Parameters,
-      execute: (params: Schema.Schema.Type<typeof Parameters>, ctx: Tool.Context) => run(params, ctx).pipe(Effect.orDie),
+      execute: run,
     }
   }),
 )