Receive webhook from Pipedream triggers (sources).

Pipedream payload structure: { "trigger": { "event": {...actual event data...} }, "context": { "emitter_id": "dc_GQu1ndJ", # This is our trigger_id "external_user_id": "ada8504b-f71d-43bb-a2b6-e227a0591771", "workflow_id": "p_brCwaLo", ... } }

This endpoint:

1. Validates Pipedream-Webhook-Key header
2. Extracts emitter_id (trigger_id) from context
3. Looks up subscriptions by trigger_id (external_subscription_id)
4. Validates subscription is active
5. Applies filters (subscription_config + filter_conditions)
6. Creates subscription events via create_and_queue_event (standardized)