Move nwis wire rendering into notifications/formatters/hydro.py and the
threshold-crossing decision into notifications/gating/hydro.py, behind
the registry under the real category `stream_flow`. handle_nwis now
builds a canonical dict, calls decide(), keeps the gauge_readings INSERT
inline (append-only), and branches on is_cutover("stream_flow") exactly
like quake_handler — legacy _attach_commit path stays byte-identical
while the new path bakes in shadow. No cutover.
- gauge_readings INSERT stays inline; decider only reads prior state
- hydro has no per-event broadcast-state table → GateResult.commit=None;
event_log.handled flip stays handler-owned in the cutover wrapper
- tier-a: golden byte-identical wire + gate-sequence parity (12 tests)
- native env/usgs.py deferred (different category vocab, no
threshold_state); non-cutover so store._emit_event won't run it
Suite at 34-failure baseline.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
