Epic: Code quality, coverage, and the lint gates #452

Plans: add-test-coverage.md ·
complexity-refactors.md ·
surface-area-refactor.md ·
audit-remediation.md

Coverage backfill, complexity reduction, exported-surface trimming, and the lint gates that keep them.

Also the phase-8 remainders that hide behind steps marked complete: the wait_until matrix rows, and the
nolint reason sweep.