Bump connect retry attempts from 3 to 8 and cap exponential backoff at
15 seconds. Old budget: 3 attempts, 1+2+4=7s total — insufficient for
cold boot on slow networks or embedded devices. New budget: 8 attempts,
1+2+4+8+15+15+15=~60s total.
Inspired by PR #5770 by @Bartok9 (re-implemented against current main
since original was 913 commits stale with conflicts).