When the preferred lightwalletd server is reachable but warming up (JSON-RPC -28
/ "Activating best chain"), the failover treated it like a dead server and fell
through to the others, so the wallet didn't open until the next 20s retry — even
though the healthy server was ready within seconds.
Detect the warmup error during failover, flag it on the open outcome
(lastOpenWasWarmup()), and have the App retry on a short ~4s interval in that case
instead of 20s, so the wallet opens promptly once warmup clears. A unit test
covers a warming-preferred + dead-fallback open setting the flag.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>