Arm / refresh the dead-man switch
Arm (or heartbeat-refresh) the caller’s gateway dead-man switch. Sets the deadline to now + timeout_ms;
calling again refreshes it. When a tick reaches an armed deadline the
gateway fires one user-wide MASS_CANCEL and disarms (fire-once). This is
the gateway fairy dead-man, NOT Kalshi order-group fill-velocity limiting
(which stays deferred). Closed schema — an unknown field is 400 unknown_field; a timeout_ms outside 1000..=60000 is 400 invalid_timeout.
Authorizations
The public API key (alphanumeric access_key string).
Request timestamp, Unix milliseconds (decimal). ±5000 ms replay window.
base64(HMAC-SHA256(secret, "timestamp\nMETHOD\npath?query\nbody")). For the WS handshake the body is empty and the path is /v1/ws.
Body
Arm / refresh the dead-man switch.
Heartbeat budget in milliseconds. On the first tick at or after now + timeout_ms the gateway fires one user-wide MASS_CANCEL and disarms (fire-once). Re-arm to refresh the deadline.
1000 <= x <= 60000