Fine-tuning
Training a copy of a model further on your own examples, so that it leans towards your format or style. It changes tendencies. It isn't a way of giving a model your code base, which changes daily anyway.
People reach for it to teach an agent about their project. Instructions and search almost always do that better: they cost little, can be edited in a minute, and are in the repo where you can review them.
Say it to your agent
“Don't fine-tune for this. Put our naming conventions in AGENTS.md with three real examples from src/, then run the same task twice and show me whether the output now matches.”