Well you can use an LLM similarly. Have it write docs for all your files including a summary for each function / class, ideally in order of dependency. Then use only the summaries in context. This should significantly lower your token count.
In my experience, you often remember and/or discover relationships to other parts of the system during the current development task, by delving into the implementation. These relationships also aren't necessarily explicit in the code you're looking at. For example, they can relate to domain-level invariants or to shared resources, or simply shared patterns and conventions. In general you can't prepare everything that would be relevant up front.
Haven't tried it personally but it should work