Fix a SYSVOL sync service that terminated itself, and record the test results

Deploying the image found a real defect. adc-sysvol-sync.service declared
Requires=samba-ad-dc.service, and the sync restarts samba-ad-dc after copying
idmap.ldb. systemd stops units that *require* a service being restarted, so the
sync killed itself with SIGTERM part way through:

  adc-sysvol-sync[2065]: syncing idmap.ldb from 10.10.10.22 (one time)
  adc-sysvol-sync.service: Main process exited, code=killed, status=15/TERM
  adc-sysvol-sync.service: Failed with result 'signal'

The timer started it again and the second run succeeded, so the end state looked
correct while the mechanism was broken — the kind of fault that stays hidden
until it matters. The dependency is Wants= now, which gives the ordering without
the stop propagation, and the restart is --no-block.

The image was tested end to end: two DCs deployed from MAAS, the first
provisioning the domain in 21 seconds and the second joining in 23, both
unattended and on the first attempt. DRS replication is healthy, the FSMO roles
sit where they should, and a file written into SYSVOL on one DC reached the other
within a timer interval, ACLs reset.

A Windows Server 2025 machine then joined the domain: it found the DC through the
_ldap._tcp.dc._msdcs SRV record, Add-Computer succeeded, and after rebooting the
secure channel tested good. nltest reports the DC with the full set of
capabilities Windows expects — PDC GC DS LDAP KDC TIMESERV GTIMESERV WRITABLE
DNS_DC DNS_DOMAIN DNS_FOREST FULL_SECRET. Group Policy refresh completed, and
LDAP queries from the client listed both DCs, the Windows machine account and the
domain users.

One genuine limitation surfaced and now has its own section: Samba does not
implement ADWS, so port 9389 is closed and the PowerShell ActiveDirectory module
cannot be used against these DCs. ADUC, ADSI and raw LDAP are unaffected, which
is what the LDAP queries above demonstrate.

Verified status now separates what was observed from what was not. Notably still
untested: applying an actual GPO, an interactive domain logon, seizing FSMO roles
after losing a DC, BIND9_DLZ, and real bare metal.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

overlay/etc/systemd/system/adc-sysvol-sync.service

@@ -4,7 +4,11 @@
 Description=Replicate SYSVOL from another domain controller
 Documentation=https://wiki.samba.org/index.php/SysVol_replication_(DFS-R)
 After=samba-ad-dc.service
-Requires=samba-ad-dc.service
+# Wants=, deliberately not Requires=. The sync restarts samba-ad-dc after it
+# copies idmap.ldb, and a Requires= dependency makes systemd stop this unit when
+# the thing it requires restarts - so the sync killed itself mid-run with
+# SIGTERM. Ordering is all that is wanted here; the script checks for SYSVOL.
+Wants=samba-ad-dc.service
 ConditionPathExists=/etc/adc-maas/sysvol-sync.conf
 
 [Service]