Case-only email edits (test → Test) skipped the ClientRecord rename
because the gate used strings.EqualFold. SyncInbound then failed its
case-sensitive lookup and inserted a second row; the later fallback
rename hit UNIQUE constraint failed: clients.email.
Rename on any byte-level email difference so the same client is updated
in place.
Fixes#5951
Update committed an email rename to the clients table with a standalone
write before the per-inbound loop rewrote each inbound's settings JSON.
In that window the record held the new email while the JSON still held
the old one, so any concurrent SyncInbound (traffic poll, another edit)
found no record for the old email and inserted a duplicate seeded from
the stale JSON - carrying the same subId, which then failed every later
edit with "Duplicate subId". The subId collision check also ran after
that write, so even a rejected update permanently renamed the email.
Move the rename inside UpdateInboundClient's serialized transaction,
next to the settings save and SyncInbound, so no other writer can see
one without the other; skip it when a record already owns the target
email (the merge case). Update now only runs collision checks before
the loop and falls back to a direct rename solely for records with no
attached inbound. This covers both the REST API and the web UI editor,
which share this path.
Closes#5870
H-TTTTT