v1.9.422 — modularize driftCheckCmd to lib/drift.js (UR-0125)
Third large-handler extraction for bin heaviness: moved the 322-line drift check handler (recursion + self-spawn) to lib/drift.js via DI (test-driven, deps resolved in stages). bin 20617 to 20318 lines (cumulative -859). Behavior unchanged. selftest 167 to 168, e2e 421 to 422, zero regression.