You don't have to maintain it. LLMs are really good at following direction.
I have a custom agent that can take python code, translates it to C, does a refactoring job to include a mempool implementation (so that memory is allocated once at the start of the program and instead of malloc it grabs chunks out of mempool), runs cppcheck, uploads to a container, and runs it with valgrind.
Been using it since ChatGPT3 - the only updates I did to it was API changes to call different providers. Doesn't use any agent/mcp/tools thing either, pure chat.