Successor to milestone #18 (closed 2026-07-17 but still actively receiving closed issues through 2026-07-20 — the grab-bag of general self-host correctness bugs, test-coverage gaps, and feature work across apps/, packages/, src/, .github/, scripts/** never stopped being a real need, it just lost its open home). Created 2026-07-21 after an adversarial re-check found the contributor-available floor had collapsed because this was the only milestone catching ordinary (non-Cloud-Readiness) engineering work and it had no open successor.