The panel driver now splits writing a frame into its SPI buffer
(epd_write_frame(), which also computes a CRC32 as it streams) from
actually triggering the physical refresh (epd_turn_on_display()).
frame_client.c compares the new CRC against the last one that was
actually refreshed (persisted in NVS) and skips the refresh entirely
when they match -- e.g. a reboot redisplaying the same photo before the
server's refresh interval elapsed no longer causes a visible flash for
no visual change.
Also reorders the per-wake fetch cycle: the image fetch (15s timeout)
now goes before the config check (3s timeout), instead of after. The
config check's tighter timeout was intermittently tripping on
connection-setup latency that's common on the first request after
waking from a long deep sleep (e.g. stale ARP); putting the more
tolerant request first absorbs that latency, and the config check then
rides the connection it already warmed up.