renderMapTiles already queues every visible tile (edges + corners) on pan,
and queueTileForFetch marks each one 'seen' the instant it is queued. But the
fetch worker only cleared that mark on success — so a tile whose download hit a
TRANSIENT failure stayed flagged forever and was never re-queued. The heap-
safety gate is the common trigger: during a pan the render thread is decoding a
burst of tiles (heavy internal-DRAM use), so the worker's <12 KB-free skip trips
for several of the freshly-queued edge/corner tiles, which then sit blank until
the user forces a full 'reload tiles'. Wi-Fi blips, a full tile cache and proxy
5xx/timeouts had the same one-shot-and-stuck behaviour.
Add tileFetchForget() and drop the 'seen' mark on every transient failure
(heap gate, Wi-Fi down, cache full, negative/5xx/408/429 HTTP, disk write
hiccup) so the next render miss re-queues the tile automatically. A permanent
4xx rejection still stays marked so we don't re-hammer genuinely-absent tiles.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
