I added coverage reporting and enforced a minimum threshold in CI, expanded unit and integration tests (including Firestore rules and critical server endpoints), implemented a billing integration with secure webhook handling to update plan fields, incrementally migrated legacy HTML pages into React components—prioritizing high‑traffic and complex pages and retiring the static files after verifying parity and tests—added linting, dependency and secret scanning to CI, and hardened operations with health/metrics checks and deployment documentation.