Define project acceptance
Record the deliverables, checks and known limitations that determine completion. Separate defects against that scope from newly requested behavior.
List continuing responsibilities
Updates, monitoring, backups, content changes and incident response need owners after launch. Some may belong to your team or another provider.
Choose a maintenance model
Agree coverage, available effort, priorities and exclusions. A maintenance relationship can include planned improvements, but the process for selecting them should be clear.
Keep knowledge available
Preserve source, configuration, access ownership and operating instructions. Good handover reduces avoidable dependence without pretending that future maintenance is unnecessary.