feat(background-agent): add per-key queue structure

src/features/background-agent/manager.ts

@@ -49,6 +49,11 @@ interface Todo {
   id: string
 }
 
+interface QueueItem {
+  task: BackgroundTask
+  input: LaunchInput
+}
+
 export class BackgroundManager {
   private static cleanupManagers = new Set<BackgroundManager>()
   private static cleanupRegistered = false
@@ -65,6 +70,9 @@ export class BackgroundManager {
   private config?: BackgroundTaskConfig
 
 
+  private queuesByKey: Map<string, QueueItem[]> = new Map()
+  private processingKeys: Set<string> = new Set()
+
   constructor(ctx: PluginInput, config?: BackgroundTaskConfig) {
     this.tasks = new Map()
     this.notifications = new Map()
@@ -252,6 +260,13 @@ export class BackgroundManager {
     return undefined
   }
 
+  private getConcurrencyKeyFromInput(input: LaunchInput): string {
+    if (input.model) {
+      return `${input.model.providerID}/${input.model.modelID}`
+    }
+    return input.agent
+  }
+
   /**
    * Track a task created elsewhere (e.g., from delegate_task) for notification tracking.
    * This allows tasks created by other tools to receive the same toast/prompt notifications.
@@ -1129,6 +1144,8 @@ Use \`background_output(task_id="${task.id}")\` to retrieve this result when rea
     this.tasks.clear()
     this.notifications.clear()
     this.pendingByParent.clear()
+    this.queuesByKey.clear()
+    this.processingKeys.clear()
     this.unregisterProcessCleanup()
     log("[background-agent] Shutdown complete")