fix: hide task background instructions by default (#27872)

packages/opencode/src/tool/task.ts

@@ -24,6 +24,14 @@ export interface TaskPromptOps {
 }
 
 const id = "task"
+const BACKGROUND_DESCRIPTION = [
+  "",
+  "",
+  [
+    "Background mode: background=true launches the subagent asynchronously.",
+    "Use task_status(task_id=..., wait=false) to poll, or wait=true to block until done.",
+  ].join(" "),
+].join("\n")
 
 const BaseParameters = Schema.Struct({
   description: Schema.String.annotate({ description: "A short (3-5 words) description of the task" }),
@@ -327,7 +335,7 @@ export const TaskTool = Tool.define(
     })
 
     return {
-      description: DESCRIPTION,
+      description: flags.experimentalBackgroundSubagents ? DESCRIPTION + BACKGROUND_DESCRIPTION : DESCRIPTION,
       parameters: Parameters,
       jsonSchema: flags.experimentalBackgroundSubagents ? undefined : ToolJsonSchema.fromSchema(BaseParameters),
       execute: (params: Schema.Schema.Type<typeof Parameters>, ctx: Tool.Context) =>