The Discord adapter could enter a silent zombie state after a network
outage / proxy stall: the process is alive, _client looks open, but the
underlying socket is dead. discord.py's WebSocket reconnect never sees a
RST through a wedged proxy/NAT, so client.start() spins forever without
exiting — which means the bot-task done callback (which only fires on
task completion) never trips either. The bot stays "offline" in Discord
until a manual `hermes gateway restart`. Reported offline for 13-17h.
Adds an out-of-band REST liveness probe in DiscordAdapter. Every
`discord.liveness_interval_seconds` (default 60s) the adapter issues a
cheap fetch_user(bot_id) — the same REST path as message delivery, so it
fails when the proxy/NAT is wedged. After
`discord.liveness_failure_threshold` consecutive failures (default 3) the
probe closes the wedged client and surfaces a retryable fatal error,
which trips the gateway's existing _platform_reconnect_watcher and
rebuilds the adapter. Operators disable it by setting either knob to 0.
Config lives in config.yaml (discord.liveness_*) per the .env-is-secrets
policy; _apply_yaml_config bridges it to internal env vars the adapter
reads, matching the existing HERMES_DISCORD_TEXT_BATCH_* pattern.
Co-authored-by: Hermes Agent <agent@nousresearch.com>
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