Canvas (prev commit) made the big-track map self-recover but the Chromium
compositor still hit 'tile memory limits exceeded' ~46x and 10k segments
still janked. Three cheap levers:
- tilecache: keepBuffer 2->1 and updateWhenZooming:false - fewer retained
off-screen tiles in the compositor's raster budget on a high-DPI screen.
- track/roads polylines: smoothFactor 2.5 (Douglas-Peucker in pixels) - a
10k-point track draws far fewer segments zoomed out, full detail zoomed in.
- POI: cap markers by zoom (z>=16:500, 15:200, 14:80, 13:30) instead of a
flat 500 - a handful near min-zoom, everything only when zoomed in close.
Two fixes to the dark map + offline tiles:
- Dark backdrop: body.dark-map also darkens .leaflet-container (was #ddd), so
the light Leaflet background no longer flashes bright between/behind tiles
while zooming or where a tile is missing.
- Tile caching: createTile fetched the display <img> from the URL but cached
via a SEPARATE fetch — on a flaky mobile link that second request often
failed, so tiles showed but were never cached and re-zooming re-fetched them.
Now one fetch caches and displays from the same blob, so every shown tile is
cached. CSP already allows connect-src to the OSM tile host.
Verified on device: container bg rgb(27,31,36) under dark map; IndexedDB tile
cache populated.
