Baseline first
Record account, region, instance, disk, memory, ports, containers, networks, volumes, proxy rules, certificates, and current health. Without a baseline, you cannot prove the deployment caused no regression.
Isolate every collision point
Use an independent directory, Compose project, network, container name, volume, secrets, internal port, and hostname. Add an exact reverse-proxy rule without rewriting shared defaults.
Verify new and old together
Check new-app health, domain, TLS, and critical flow while re-reading old-project health and public response. A successful deployment response is not production-convergence evidence.