◇ Could this help me?
Yes. This is a straightforward context-management win: a shorter always-loaded index plus rules that attach to the files they govern means less irrelevant context per session and rules that are easier to keep accurate. The verification step matters as much as the split, so confirm what actually loaded rather than assuming the scoping worked. This is a general practice.
This project's instructions file has grown too large. Split it into topic-scoped rule files under a rules folder, each bound to the paths it actually governs, and reduce the main file to a short index that points at them. Preserve every existing rule, tell me which ones were ambiguous about scope so I can decide where they belong, and then show me how to verify which rules load when I edit a specific file.