fix(background-task): return result instead of status for completed tasks

- Fix background_output to check completion status before block flag
- Update call_omo_agent return message to correctly indicate block=false as default
- Add system notification guidance in return message

🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/tools/background-task/tools.ts

@@ -211,12 +211,7 @@ export function createBackgroundOutput(manager: BackgroundManager, client: Openc
         const shouldBlock = args.block === true
         const timeoutMs = Math.min(args.timeout ?? 60000, 600000)
 
-        // Non-blocking: return status immediately
-        if (!shouldBlock) {
-          return formatTaskStatus(task)
-        }
-
-        // Already completed: return result immediately
+        // Already completed: return result immediately (regardless of block flag)
         if (task.status === "completed") {
           return await formatTaskResult(task, client)
         }
@@ -226,6 +221,11 @@ export function createBackgroundOutput(manager: BackgroundManager, client: Openc
           return formatTaskStatus(task)
         }
 
+        // Non-blocking and still running: return status
+        if (!shouldBlock) {
+          return formatTaskStatus(task)
+        }
+
         // Blocking: poll until completion or timeout
         const startTime = Date.now()