Incident 2 of #109521: a Gateway socket can stay ESTABLISHED and keep
ACKing heartbeats while zero DISPATCH events are parsed, so every
transport-side liveness sample (ready/open/ack-age/latency) reads
healthy for hours. The merged #109963 deliberately dropped the
event_silence dimension: a raw-frame stamp is debug-gated
(on_socket_raw_receive needs enable_debug_events) and, since heartbeat
ACKs are frames, ack_stale always fires first by construction.
This adds the dispatch-side signal that was requested instead:
- stamp on on_socket_event_type, which discord.py 2.7.1 dispatches for
every parsed DISPATCH frame with no debug gate (verified live against
the real received_message path: 4/4 frames fired with
enable_debug_events=False, on_socket_raw_receive 0/4)
- new knob websocket_event_max_silence_seconds (default 4h, the
incident report's field-proven operator bound); 0 opts out of this
dimension ONLY — the #109782 review failure put the knob in
_start_liveness_probe's all-or-nothing guard, killing the whole
watchdog; it is gated strictly inside _read_websocket_health here
- the stamp resets per connection (connect() clears it), and a None
stamp (no event parsed yet on this connection) is not silence
- docs (en + zh-Hans) cover the new knob and the per-dimension opt-out
Fixes#109521
(cherry picked from commit b4baa97fc45794209711a45e052111d7d44d5f90)
101861c7f7