One-off script to populate the new device_serials array for assignments
made before the assign/unassign sync existed. Treats each device's
user_list as the source of truth and sets every user's device_serials to
exactly the matching serials, so re-running it is a no-op.
Dry run by default; --apply writes (batched, <=400 per commit).
It also reports users whose doc ID != uid field (MQTT resolves users by the
uid field), users with no uid, devices with users but no serial, and
user_list entries pointing at non-existent users. user_list entries are
accepted as DocumentReferences, "users/{id}" paths or raw doc IDs, and an
entry that matches a uid field rather than a doc ID is mapped to its doc.
Dry run against current data: 13 devices, 13 users, 11 users to update,
0 doc-ID/uid mismatches, 1 dangling user_list entry
(Cx2Va72sUzDbr1T8Ebbh on BSVSPR-26I047-STD10R-88YFJP).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
