fix: address Cubic background-agent issues — task status filter, array response handling, error mapping, concurrency key, duration fallback, output validation

src/features/background-agent/task-queries.ts

@@ -45,7 +45,7 @@ export function getRunningTasks(tasks: Iterable<BackgroundTask>): BackgroundTask
 }
 
 export function getCompletedTasks(tasks: Iterable<BackgroundTask>): BackgroundTask[] {
-  return Array.from(tasks).filter((t) => t.status !== "running")
+  return Array.from(tasks).filter((t) => t.status === "completed")
 }
 
 export function hasRunningTasks(tasks: Iterable<BackgroundTask>): boolean {