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- /api/ice: when TURN_SECRET is set, mint short-lived HMAC credentials (coturn use-auth-secret) so no permanent password is exposed and the relay can't be abused. Static TURN_USERNAME/CREDENTIAL still supported. - share.html: connection watchdog + clear "couldn't connect on this network" message instead of a blank screen when no path can be established. - deploy/coturn: ready-to-run turnserver.conf + docker-compose + README for hosting our own TURN on a VM we own (flat cost, no per-GB billing). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>