phase-03 Step 3.4 (dc0): G3 domain-manager probe -- named check + live PASS ...

Build scripts/g3-domain-manager-probe.sh + tests/g3-domain-manager-probe (harness
12/12, every exit path proven) as the GA-R6 named executable check for phase-03
Step 3.4 stage 2 (gate G3), filling the hard-rule-4 gap (was a manual runbook walk
only) and giving dc1's Step 7 a reusable probe. Grounded in the real policy
(domain-manager-policy.yaml:103 create_grant managed-role guard).

Ran it LIVE from the dc0 rack (operator-approved): G3 PASS, 7 ok / 0 fail, teardown
verified clean (zero g3-* residue). Stage-1 (PO:) verified read-only: policyd-override
attached, all 3 keystone units 'PO: Unit is ready'. Capture
docs/audit/g3-dc0-probe-20260806.txt.

HARNESS-MANIFEST recorded 99->100; gauntlet ALL GREEN (100), repo-lint 0 fail.
CURRENT-STATE: Step 3.4 -> RESOLVED; phase-03 exit gate now turns on the Horizon
reachable/login-works item (D-044/D-075 per-rebuild + VR0-nginx vs VR1-tailnet access
model = Decision C), to be measured + ruled next.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Fg98z7QyzwYUs8fsWCn728