Discovered during the 2026-04-19 registry:2.8.3 pin deploy: nginx caches
its upstream DNS at startup and does NOT re-resolve after registry-*
containers are recreated. Symptom was /v2/_catalog returning
{"repositories": []} and /v2/ returning 200 without auth — nginx was
forwarding to a stale IP that a different backend container now owns.
Fix is always 'docker restart registry-nginx' after any registry-*
bounce. Captured in registry-vm.md so future manual operators and the
coming auto-sync pipeline (beads code-3vl) both encode the step.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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