How to organize control over clients on their hosting?

Question

git

We have our own assembly on WP, on the basis of which we assemble client sites. We control our developers through code review (git), no questions asked. But when we upload the site to the client's production, control is lost. We keep logs in WP in order to see the work with the content, but let's say the customer got into the code, that the thread broke there and turns to us that they say there are problems with our assembly ... How can we monitor this? What changes were made to the code, who made them, etc.

Answer 1

How can you follow this?

Why follow this? You can see the nature of the problem here. Found a problem - told the client whose fault it was. The fact that he climbed into the code is not a guarantee that the problem is because of him.
And clients do not mind that you spend their server resources so unreasonably?

Answer 2

The most obvious option is to create a checksum base for files after uploading and setting.
If someone changes the code, you will immediately know by simply running checksum. And then diff to the modified file and watch the changes.