If you drop Claude into a -file repo and ask "what does this codebase do?", it will try to read everything and burn through your context window, so start specific.
Ask for an overview of one directory at a time. "What's the structure of src/services/?" uses a directory @ reference without reading every file. When you need to find something, describe it precisely: "Find where HTTP errors are handled" lets Claude use Grep instead of reading files one by one. I'll use Glob to narrow scope before asking Claude to read: "Find all files matching **/auth/**" before "read these files". Working in focused passes beats loading the whole repo into context at once.