Phase 2: Job enqueueing from counter

- Add backend/jobs.py with enqueue_random_number_job function
- Modify counter increment endpoint to enqueue job after incrementing
- Add mock_enqueue_job fixture to conftest.py for all tests
- Add test_increment_enqueues_job_with_user_id to verify correct user_id
- Job is enqueued synchronously; failure causes request to fail

backend/routes/counter.py

@@ -1,11 +1,12 @@
 """Counter routes."""
 
-from fastapi import APIRouter, Depends
+from fastapi import APIRouter, Depends, HTTPException
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from auth import require_permission
 from database import get_db
+from jobs import enqueue_random_number_job
 from models import Counter, CounterRecord, Permission, User
 
 router = APIRouter(prefix="/api/counter", tags=["counter"])
@@ -38,7 +39,7 @@ async def increment_counter(
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(require_permission(Permission.INCREMENT_COUNTER)),
 ) -> dict[str, int]:
-    """Increment the counter and record the action."""
+    """Increment the counter, record the action, and enqueue a random number job."""
     counter = await get_or_create_counter(db)
     value_before = counter.value
     counter.value += 1
@@ -49,5 +50,15 @@ async def increment_counter(
         value_after=counter.value,
     )
     db.add(record)
+
+    # Enqueue random number job - if this fails, the request fails
+    try:
+        await enqueue_random_number_job(current_user.id)
+    except Exception as e:
+        await db.rollback()
+        raise HTTPException(
+            status_code=500, detail=f"Failed to enqueue job: {e}"
+        ) from e
+
     await db.commit()
     return {"value": counter.value}