CONC-HIGH-1: Add mutex to wsClient.miners map to prevent race condition
P2P-CRIT-2: Add MaxMessageSize config (1MB default) to prevent memory exhaustion
P2P-CRIT-3: Track pending connections during handshake to enforce connection limits
RESIL-HIGH-1: Add recover() to 4 background goroutines to prevent service crashes
TEST-CRIT-1: Create auth_test.go with 16 tests covering Basic/Digest auth
RESIL-HIGH-3: Implement circuit breaker for GitHub API with caching fallback
Also fixed: NonceExpiry validation in auth.go to prevent panic on zero interval
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
