Use the tree-shakable functional Mini API for URL and dataset schemas. Preserve parsing, date validation, fallbacks and serialization, including leap-year boundary cases.

Fresh production export: total gzip JavaScript 201.3 -> 191.1 KiB, saving 10.2 KiB. Default heap 18.7 -> 18.5 MiB; all-chart timing varied 2817.0 -> 2845.6 ms. No validation policy changes.

Checkpoint measurements above predate the final QA lifecycle/coverage fixes and are not isolated shipping effects. Combined shipping benchmark: 477.2/2934.3 ms default visible/all charts, 114 ms observed initial TBT, 18.2 MiB retained heap and 191.1 KiB gzip JS. Original baseline: 509.1/3258.9 ms, 130 ms, 18.3 MiB, 228.1 KiB. Layer 3: 569.3/4271.3 ms, 159 ms, 29.9 MiB, 202.4 KiB. Baseline dates, five API runs, three fresh contexts per page and one warmup; no concurrent QA/build/dev work. Shipping artifacts: /tmp/atlantis-frontend-overhaul/perf/layer4-shipping/results.json. Full gates pass with 220 web and 70 e2e tests.