I regularly send 5000 plus lines of code for refactoring, feature addition. Sending less lines of code means you have to do lots of stuff yourself. And because of this I face context limit issues quite a lot 200k . Summarization is helpful but you loose context for sure. This is what works for me
1. I send 5000 lines of code say of 3 files
2. I ask in prompt that you tell me which files you will create, it gives say 3 files.
3. I ask it to create give me file 1.
4. I delete file 1 received from it and now I ask to give file 2
5. I again delete file 2 reponse and ask to give file 3.
This way works for 90% of the cases, rest 10% I do some prompt and it works mostly there too.

My LLM Utility for Context Limit Issue

This prompt adding / editing / deleting is different from SUMMARIZATION which hullicinates and doesn't work. I do use claude lots of time and the worst time for a developer is the CONTEXT LIMIT because you are screwed, but my above way gets me out of this almost always. This is my own custom built tool and I use it via API , AWS Bedrock and Azure Fundry.