Add origin_app to APActivity — apps only process their own activities

Each app's EventProcessor now filters by origin_app so apps don't steal
each other's pending activities. emit_activity() and publish_activity()
auto-detect the app name from Quart's current_app.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

events/processor.py

@@ -28,9 +28,11 @@ class EventProcessor:
     def __init__(
         self,
         *,
+        app_name: str | None = None,
         poll_interval: float = 2.0,
         batch_size: int = 10,
     ):
+        self._app_name = app_name
         self._poll_interval = poll_interval
         self._batch_size = batch_size
         self._task: asyncio.Task | None = None
@@ -70,12 +72,15 @@ class EventProcessor:
         """Fetch and process a batch of pending activities. Returns count processed."""
         processed = 0
         async with get_session() as session:
+            filters = [
+                APActivity.process_state == "pending",
+                APActivity.process_attempts < APActivity.process_max_attempts,
+            ]
+            if self._app_name:
+                filters.append(APActivity.origin_app == self._app_name)
             stmt = (
                 select(APActivity)
-                .where(
-                    APActivity.process_state == "pending",
-                    APActivity.process_attempts < APActivity.process_max_attempts,
-                )
+                .where(*filters)
                 .order_by(APActivity.created_at)
                 .limit(self._batch_size)
                 .with_for_update(skip_locked=True)