Migration 0026 rebuilds the activities table to enforce UNIQUE(user_id,
garmin_activity_id) as the composite primary constraint, removing the old
global UNIQUE(garmin_activity_id) constraint from migration 0001. This
allows the same Garmin activity ID to appear for different users without
conflicts, which is essential for the per-user profile design and enables
the TestUpsertActivity_SameGarminActivityIDAllowedAcrossDifferentUsers
test to pass.
Christophe Vila
d8b722820d