Why my Chrome extension uses a hybrid AI risk score instead of pure AI sorting (opens in new tab)

I've been building PR Focus, a Chrome extension that helps developers triage GitHub pull requests. One of the first decisions I had to make was: how do I actually sort PRs by priority? The obvious answer is "use AI to score the risk". But I didn't want to rely 100% on an LLM because: AI is inconsistent (same diff, different scores). It costs users tokens on every poll. A wrong AI score can bury a broken PR. So I built a hybrid system: deterministic signals (CI status + PR age) form the floor,...