- Subscribe_returns_a_handle_for_each_backend — both backends accept
the same full-reference list and return a non-null handle, with
symmetric Unsubscribe cleanup.
- Subscribe_event_rate_within_tolerance_for_a_3s_window — counts
OnDataChange invocations on each backend across a 3s window and
asserts the mxgw/legacy ratio sits in [0.5, 1.5]. Skips when the
sampled tags don't change in the window (configuration-only Galaxy).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
