The Gateway WS health probe sampled only transport state — ready, open,
heartbeat-ACK age, latency. A socket that stays ESTAB and keeps ACKing while
zero gateway frames arrive (the #109521 "connected-but-deaf" incident) read
healthy indefinitely, and the adapter went silent for hours with no log line
and no watchdog firing.
Two defects fixed:
1. Dispatch-side dimension. `on_socket_raw_receive` now stamps
`_last_gateway_frame_at` for every inbound raw gateway frame — heartbeats
and ACKs included, so a legitimately quiet server is not flagged. The
health check gains an `event_silence` reason with its own bound,
`websocket_event_max_silence_seconds` (default 300s, 0 disables the
dimension alone). The stamp resets on `on_ready` so a reconnect never
inherits pre-restart silence. Trip path is unchanged: consecutive
failures -> retryable `discord_websocket_health_stale` -> the existing
reconnect watcher builds a fresh adapter.
2. Silent probe disable. `_finite_positive_config_float` / `_config_int`
mapped anything `float()` rejects ("15s", "nan", "true") to 0.0 with no
log line, permanently disabling the watchdog invisibly. Unparsable and
non-positive values now log one WARNING naming the knob and raw value.
The new key rides the existing `_YAML_WEBSOCKET_LIVENESS_KEYS` seeding and is
documented in the Discord guide's liveness section.
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