subscribeEvents / watch stream.
The server emits heartbeats on a fixed cadence (~30s) even when no domain
events occur. Consumers can use this signal to run a stall watchdog: if no
heartbeat arrives within a grace window, the connection is likely half-open
and the stream should be torn down and re-established. Without this hook the
heartbeat frames are silently dropped and a half-open stall is undetectable
from the event stream alone.