feat(atlas): add background task session tracking with retry scheduling

- Add background-launch-session-tracking.ts to persist delegated sessions
- Add task-context.ts for task context resolution utilities
- Modify idle-event.ts to schedule retries when background tasks are running
- Update tool-execute-after.ts to integrate session tracking
- Add comprehensive tests for background task retry behavior

🤖 Generated with assistance of OhMyOpenCode

src/hooks/atlas/idle-event.ts

@@ -90,7 +90,10 @@ function scheduleRetry(input: {
     const currentProgress = getPlanProgress(currentBoulder.active_plan)
     if (currentProgress.isComplete) return
     if (options?.isContinuationStopped?.(sessionID)) return
-    if (hasRunningBackgroundTasks(sessionID, options)) return
+    if (hasRunningBackgroundTasks(sessionID, options)) {
+      scheduleRetry({ ctx, sessionID, sessionState, options })
+      return
+    }
 
     await injectContinuation({
       ctx,
@@ -194,6 +197,7 @@ export async function handleAtlasSessionIdle(input: {
   }
 
   if (hasRunningBackgroundTasks(sessionID, options)) {
+    scheduleRetry({ ctx, sessionID, sessionState, options })
     log(`[${HOOK_NAME}] Skipped: background tasks running`, { sessionID })
     return
   }