assertViewport allowed 0.001 degrees between the centre it asked for and the centre Leaflet reports back. Leaflet keeps the centre as a pixel coordinate, so a read-back centre is only accurate to the pixel it landed on, and one pixel spans 360/(256*2^zoom) degrees: 0.02197 at zoom 6, 0.00137 at zoom 10. The flat budget demanded 1/20 of a pixel at zoom 6 while its own comment said 'allow sub-pixel coordinate rounding'.
It passes on master because the container rounds favourably. It fails as soon as the layout changes: on the ON8AR fork, whose coverage page carries one extra toolbar row, the first assertion reported {lat:11.996338401936226, lng:33.99169921875001, zoom:6} against an expected 12/34 — 0.167 px of latitude and 0.378 px of longitude, so the view was right and the assertion was wrong. Any container-height change can trip it, fork or not.
The budget is now one pixel at the asserted zoom via a degPerPixel(zoom) helper, applied to both centre assertions and to the waitForFunction on the hash (zoom 10, where 0.001 was 0.73 px and merely lucky). For latitude the Mercator scale is the longitude figure times cos(lat), so the longitude figure is the looser bound there, deliberately: this asserts the view is where we asked, not a projection identity. A one-tile miss at zoom 6 is 5.6 degrees and still fails.
Verified by arithmetic rather than locally (the suite needs a served instance and a browser): the observed drift falls inside the new budget and a one-tile miss does not. CI run 35273657579 is green, with 'RX coverage viewport browser regressions OK' in the Playwright job.
Merged by the interim maintainer without a second human reviewer: CI is the independent check.
The coverage page opened at a hardcoded [51.0, 4.8] zoom 8 regardless of deployment, ignoring /api/config/map (#2032). It now follows the same precedence as the main map (URL hash, then saved position, then /api/config/map, then [37.6, -122.1] zoom 9) and persists its own position across visits, syncing lat/lon/zoom into the hash so a view is shareable.
The saved position lives under its own key, rx-coverage-view, and the page never reads or writes the main map's map-view: sharing the configured default was the bug, sharing the session position was not. Both suites assert map-view stays untouched after a pan, so reintroducing a shared write fails instead of passing quietly.
Also fixed here: selectedRx is now percent-encoded into the hash, and a generation counter stops a late /api/config/map response or a stale 150ms layout timer from building a map for a page that was already left.
Reviewed twice. Verified by mutation rather than by reading: writing map-view too, ignoring the saved coverage position, and dropping the /api/config/map fetch each make the unit suite exit 1, so it covers the feature, the fix and the rejected alternative. The deploy.yml invocation was confirmed to land inside Run Playwright E2E tests (fail-fast) by parsing the workflow, and CI run 35261689694 is the E2E suite's first real execution: Go prints 'RX coverage viewport regressions OK' and Playwright prints 'RX coverage viewport browser regressions OK'.
Worth recording for the next reviewer: that E2E asserted localStorage.getItem('map-view'), so wiring it into deploy.yml without updating the assertion would have turned the job red on its first ever run. It was registered in scripts/non-unit-tests.json but invoked by nothing, the gap tracked as #2037.
Merged by the interim maintainer without a second human reviewer: CI and the mutation checks above are the independent checks.
Fixes#2032
efiten