Batch same-state lane rectangles only during SVG serialization. Retain native scene rectangle hit geometry, every original interval, ratio and interaction point; keep partial dash segments and transparent unknown observations. QA caught wide-interval hover loss when batching scene nodes; serialization-only batching fixes it and has near-boundary/interior regressions.

Checkpoint after label reuse: default all charts 2860.7 -> 2817.0 ms and heap 18.8 -> 18.7 MiB. Remove roughly 1185 SVG DOM coverage rectangles on the real default dashboard, retaining scene rectangles for hit testing. Unit and browser checks retain interval and coverage semantics; checkpoint timing has three-sample limits.

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.