fix(opencode): narrow subagent error details

packages/opencode/src/tool/task.ts

@@ -210,6 +210,15 @@ export const TaskTool = Tool.define(
           agent: next.name,
           parts,
         })
+        if (result.info.role === "assistant" && result.info.error) {
+          const message =
+            "message" in result.info.error.data && typeof result.info.error.data.message === "string"
+              ? result.info.error.data.message
+              : result.info.error.name
+          return yield* Effect.fail(
+            new Error(`Subagent failed (task_id: ${nextSession.id}): ${message}`),
+          )
+        }
         return result.parts.findLast((item) => item.type === "text")?.text ?? ""
       })
 

packages/opencode/test/tool/task.test.ts

@@ -3,7 +3,7 @@ import { SessionV1 } from "@opencode-ai/core/v1/session"
 import { Database } from "@opencode-ai/core/database/database"
 import { LayerNode } from "@opencode-ai/core/effect/layer-node"
 import { SessionProjector } from "@opencode-ai/core/session/projector"
-import { Deferred, Effect, Exit, Fiber, Layer } from "effect"
+import { Cause, Deferred, Effect, Exit, Fiber, Layer } from "effect"
 import { Agent } from "../../src/agent/agent"
 import { BackgroundJob } from "@/background/job"
 import { EventV2Bridge } from "@/event-v2-bridge"
@@ -96,19 +96,27 @@ 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(opts?: {
+  onPrompt?: (input: SessionPrompt.PromptInput) => void
+  text?: string
+  error?: NonNullable<SessionV1.Assistant["error"]>
+}): TaskPromptOps {
   return {
     cancel: () => Effect.void,
     resolvePromptParts: (template) => Effect.succeed([{ type: "text" as const, text: template }]),
     prompt: (input) =>
       Effect.sync(() => {
         opts?.onPrompt?.(input)
-        return reply(input, opts?.text ?? "done")
+        return reply(input, opts?.text ?? "done", opts?.error)
       }),
   }
 }
 
-function reply(input: SessionPrompt.PromptInput, text: string): SessionV1.WithParts {
+function reply(
+  input: SessionPrompt.PromptInput,
+  text: string,
+  error?: NonNullable<SessionV1.Assistant["error"]>,
+): SessionV1.WithParts {
   const id = MessageID.ascending()
   return {
     info: {
@@ -125,6 +133,7 @@ function reply(input: SessionPrompt.PromptInput, text: string): SessionV1.WithPa
       providerID: input.model?.providerID ?? ref.providerID,
       time: { created: Date.now() },
       finish: "stop",
+      error,
     },
     parts: [
       {
@@ -255,6 +264,49 @@ describe("tool.task", () => {
     }),
   )
 
+  it.instance("execute surfaces child errors with a resumable task_id", () =>
+    Effect.gen(function* () {
+      const sessions = yield* Session.Service
+      const { chat, assistant } = yield* seed()
+      const tool = yield* TaskTool
+      const def = yield* tool.init()
+
+      const exit = 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: new AbortController().signal,
+            extra: {
+              promptOps: stubOps({
+                text: "",
+                error: new SessionV1.APIError({ message: "Network connection lost", isRetryable: false }).toObject(),
+              }),
+            },
+            messages: [],
+            metadata: () => Effect.void,
+            ask: () => Effect.void,
+          },
+        )
+        .pipe(Effect.exit)
+
+      expect(Exit.isFailure(exit)).toBe(true)
+      if (Exit.isSuccess(exit)) throw new Error("expected task failure")
+      const child = (yield* sessions.children(chat.id))[0]
+      expect(child).toBeDefined()
+      const failure = Cause.squash(exit.cause)
+      expect(failure).toBeInstanceOf(Error)
+      if (!(failure instanceof Error)) throw new Error("expected Error defect")
+      expect(failure.message).toBe(`Subagent failed (task_id: ${child?.id}): Network connection lost`)
+    }),
+  )
+
   it.instance("execute asks by default and skips checks when bypassed", () =>
     Effect.gen(function* () {
       const { chat, assistant } = yield* seed()