The cross-instance sync silently drops tasks when x_fc_tech_sync_id is
missing on the technician, and silently collapses duplicates via dict
comprehension. Both make sync break in ways that are invisible until
someone notices a missing task on the other instance.
- _get_remote_tech_map / _get_local_syncid_to_uid: warn on duplicates
- _push_tasks_to_remote: info-log when a task is skipped because the
tech has no sync_id or no remote counterpart
- res.users onchange: warn in the form when entering a sync_id that
is already used by another active field staff
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
