fix(background-cancel): skip notification when user explicitly cancels tasks

- Add skipNotification option to cancelTask method
- Apply skipNotification to background_cancel tool
- Prevents unwanted notifications when user cancels via tool

src/features/background-agent/manager.ts

@@ -832,7 +832,7 @@ export class BackgroundManager {
 
   async cancelTask(
     taskId: string,
-    options?: { source?: string; reason?: string; abortSession?: boolean }
+    options?: { source?: string; reason?: string; abortSession?: boolean; skipNotification?: boolean }
   ): Promise<boolean> {
     const task = this.tasks.get(taskId)
     if (!task || (task.status !== "running" && task.status !== "pending")) {
@@ -878,7 +878,6 @@ export class BackgroundManager {
     }
 
     this.cleanupPendingByParent(task)
-    this.markForNotification(task)
 
     if (abortSession && task.sessionID) {
       this.client.session.abort({
@@ -886,6 +885,13 @@ export class BackgroundManager {
       }).catch(() => {})
     }
 
+    if (options?.skipNotification) {
+      log(`[background-agent] Task cancelled via ${source} (notification skipped):`, task.id)
+      return true
+    }
+
+    this.markForNotification(task)
+
     try {
       await this.notifyParentSession(task)
       log(`[background-agent] Task cancelled via ${source}:`, task.id)

src/features/context-injector/injector.ts

@@ -146,14 +146,14 @@ export function createContextInjectorMessagesTransformHook(
         return
       }
 
-      // synthetic part 패턴 (minimal fields)
+      // synthetic part pattern (minimal fields)
       const syntheticPart = {
         id: `synthetic_hook_${Date.now()}`,
         messageID: lastUserMessage.info.id,
         sessionID: (lastUserMessage.info as { sessionID?: string }).sessionID ?? "",
         type: "text" as const,
         text: pending.merged,
-        synthetic: true,  // UI에서 숨겨짐
+        synthetic: true,  // hidden in UI
       }
 
       lastUserMessage.parts.splice(textPartIndex, 0, syntheticPart as Part)