fix: make event_queue.event_id NOT NULL after backfill and writer updates

[coderabbitai]

Follow-up: Enforce NOT NULL on event_queue.event_id

The event_id column added to event_queue in #1533 is currently nullable to support a staged rollout and backward compatibility during migration. However, PostgreSQL treats NULL values as distinct, which means the unique constraint event_queue_name_event_id on (name, event_id) does not deduplicate rows where event_id is NULL. This weakens the deduplication guarantee that the PR aims to establish.

Action Required

Once the following conditions are met:

1. The backfill script (views/044_event_queue_event_id_backfill.sql) has been applied and all existing rows have a non-null event_id.
2. All writer code paths have been updated to populate event_id with a non-null UUID.

A follow-up migration should be applied:

ALTER TABLE event_queue ALTER COLUMN event_id SET NOT NULL;

This ensures the uniqueness constraint fully enforces deduplication as intended.

References

• PR: fix: add event_id to event_queue and use that for the index #1533
• Review comment: fix: add event_id to event_queue and use that for the index #1533 (comment)
• Requested by: @adityathebe