feat: add experimental background subagents (#27084)

packages/opencode/test/session/snapshot-tool-race.test.ts

@@ -30,6 +30,7 @@ import { TestLLMServer } from "../lib/llm-server"
 // Same layer setup as prompt-effect.test.ts
 import { NodeFileSystem } from "@effect/platform-node"
 import { Agent as AgentSvc } from "../../src/agent/agent"
+import { BackgroundJob } from "@/background/job"
 import { Git } from "../../src/git"
 import { Bus } from "../../src/bus"
 import { Command } from "../../src/command"
@@ -125,6 +126,7 @@ function makeHttp() {
     lsp,
     mcp,
     AppFileSystem.defaultLayer,
+    BackgroundJob.defaultLayer,
     status,
     SyncEvent.defaultLayer,
   ).pipe(Layer.provideMerge(infra))