Stability:
- transient timeouts no longer classified as ISP blocking; they fall
through to retry backoff (hard blocks - DNS/RST/cert - still abort)
- connectivity change now closes idle Go connections in every network
mode (debounced), so pooled sockets from the old interface are not
reused after a wifi/cellular handoff
- download body reads get a 60s stall watchdog that cancels and
surfaces a retryable network error instead of hanging; distinct
from user cancellation
- ResponseHeaderTimeout 45s on all transports; IdleConnTimeout 90->60s;
dial timeout 30->10s; retry backoff gains full jitter; Retry-After
honored on 5xx and Deezer 429
Data usage / speed:
- cover downloads deduplicated with singleflight plus a 24MB/15min
in-memory cache keyed by final URL (album batches fetched the same
1800px cover once per track before)
- song.link availability cached (30min positive / 5min negative)
in front of the 9-req/min rate limiter
- uTLS Cloudflare path now pools one HTTP/2 connection per host with
a shared TLS session cache instead of a full handshake per request
Deezer artist track-count N+1 kept: counts feed the discography
download UI and are already amortized by the artist TTL cache.