diff --git a/work/tests/test_native_hydro_gauge_alerts.py b/work/tests/test_native_hydro_gauge_alerts.py
new file mode 100644
index 0000000..c47abfe
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+++ b/work/tests/test_native_hydro_gauge_alerts.py
@@ -0,0 +1,323 @@
+"""fix/native-gauge-flood-alerts: native USGS gauge flood alerts are renderable.
+
+Before this fix, env/usgs.py emitted `stream_flood_warning` / `stream_high_water`
+Events that had NO registered decider and NO registered formatter -- they were
+silently dropped by store._emit_event / compose_mesh_message (see
+notifications/gating/__init__.py's old "deferred follow-up" comment and
+notifications/formatters/__init__.py's old "deferred" comment, both since
+updated). This file proves the fix along three axes:
+
+1. Registration: both native categories now resolve a decider AND a formatter
+   (mirrors TestRegistration in test_hydro_refactor.py, which covers the
+   Central-only `stream_flow` category).
+2. Gate behavior: a first elevated reading broadcasts, a sustained (same-band)
+   reading suppresses, an escalation broadcasts again -- reusing the SAME
+   hydro.decide() gate the Central path uses, now also fed by env/usgs.py's
+   to_event() (which populates event.data with the canonical schema the gate
+   and formatter both expect -- previously event.data was left empty for
+   native events).
+3. Golden wire format: formatters.hydro.format() renders a native event the
+   same way it renders a Central `stream_flow` event (test_hydro_refactor.py
+   already proves that formatter is byte-identical to the old
+   central.nwis_handler._render()) -- captured here for the native shape
+   specifically, where flow_cfs is always None (env/usgs.py's to_event() only
+   ever emits stage/height readings; a paired discharge reading, if any,
+   arrives as its own separate Event with no flood_status and never reaches
+   to_event() -- see the docstring added to to_event()/decide() for detail).
+"""
+from __future__ import annotations
+
+import time
+from unittest.mock import MagicMock
+
+import pytest
+
+from meshai.env.usgs import USGSStreamsAdapter
+from meshai.persistence import close_thread_connection, init_db
+from meshai.persistence import db as persistence_db
+from tests.harness.goldens import assert_byte_identical
+
+
+# ── DB fixture (same shape as test_hydro_refactor.py / test_nwis_handler.py) ─
+
+@pytest.fixture
+def mem_db(monkeypatch, tmp_path):
+    db_path = str(tmp_path / "native-hydro-test.sqlite")
+    monkeypatch.setenv("MESHAI_DB_PATH", db_path)
+    persistence_db._initialised.clear()
+    close_thread_connection()
+    conn = init_db()
+    yield conn
+    close_thread_connection()
+    persistence_db._initialised.discard(db_path)
+
+
+@pytest.fixture
+def adapter():
+    config = MagicMock()
+    config.sites = []
+    config.tick_seconds = 900
+    config.flood_thresholds = {}
+    return USGSStreamsAdapter(config)
+
+
+def make_reading(*, site_id="13186000", site_name="Snake River at Heise",
+                  value, flood_status, ts, lat=43.612, lon=-111.654):
+    """Mirrors the internal event dict env/usgs.py's _fetch() stores."""
+    now = time.time()
+    return {
+        "source": "usgs",
+        "event_id": f"{site_id}_height",
+        "event_type": "Stream Gauge",
+        "headline": f"{site_name}: {value} ft" + (f" — {flood_status}" if flood_status else ""),
+        "severity": "priority" if flood_status and "Flood" in flood_status else "routine",
+        "lat": lat,
+        "lon": lon,
+        "expires": now + 1800,
+        "fetched_at": now,
+        "properties": {
+            "site_id": site_id,
+            "site_name": site_name,
+            "parameter": "Gage height",
+            "value": value,
+            "unit": "ft",
+            "timestamp": ts,
+            "flood_status": flood_status,
+            "flood_stages": {"action_stage": 9.0, "flood_stage": 10.5},
+        },
+    }
+
+
+# ─────────────────────────────────────────────────────────────────────────────
+# 1. Registration — both native categories resolve a decider AND a formatter
+# ─────────────────────────────────────────────────────────────────────────────
+
+class TestRegistration:
+    @pytest.mark.parametrize("category", ["stream_flood_warning", "stream_high_water"])
+    def test_decider_registered(self, category):
+        from meshai.notifications.gating import get_decider
+        from meshai.notifications.gating.hydro import decide
+        assert get_decider(category) is decide
+
+    @pytest.mark.parametrize("category", ["stream_flood_warning", "stream_high_water"])
+    def test_formatter_registered(self, category):
+        from meshai.notifications.formatters import get_formatter
+        from meshai.notifications.formatters.hydro import format as hfmt
+        assert get_formatter(category) is hfmt
+
+    @pytest.mark.parametrize("category", ["stream_flood_warning", "stream_high_water"])
+    def test_decider_is_not_the_earthquake_decider(self, category):
+        """Regression guard: these categories must never resolve to the
+        seismic/earthquake gate, even though get_toggle() names the shared
+        family 'seismic' (see test_water_v057.py — that mapping is
+        intentional and pre-existing: stream_flow already lives on the same
+        toggle, and every water/hydro registry entry is guarded by
+        test_alert_categories_water_complete)."""
+        from meshai.notifications.gating import get_decider
+        from meshai.notifications.gating.quake import decide as quake_decide
+        assert get_decider(category) is not quake_decide
+
+    @pytest.mark.parametrize("category", ["stream_flood_warning", "stream_high_water"])
+    def test_native_always_decide(self, category):
+        """Both categories are forced onto the live decider+formatter path
+        unconditionally (independent of MESHAI_CUTOVER_CATEGORIES), exactly
+        like the native WFIGS fire categories -- required because Central
+        never emits these two category strings, so there is no shadow-bake
+        window to wait out."""
+        from meshai.notifications.cutover import NATIVE_ALWAYS_DECIDE
+        assert category in NATIVE_ALWAYS_DECIDE
+
+
+# ─────────────────────────────────────────────────────────────────────────────
+# 2. Gate behavior — first crossing broadcasts, sustained state suppresses
+# ─────────────────────────────────────────────────────────────────────────────
+
+class TestGateBehavior:
+    def _decide(self, adapter, evt):
+        from meshai.notifications.gating import get_decider
+        from meshai.notifications import clock
+        event = adapter.to_event(evt)
+        assert event is not None, "adapter unexpectedly suppressed the reading"
+        decider = get_decider(event.category)
+        gate = decider(event.data, source=event.source, now=clock.now())
+        event.data.update(gate.data_patch)
+        return event, gate
+
+    def test_first_elevated_reading_broadcasts(self, adapter, mem_db):
+        """A fresh site (no prior gauge_readings row) at action stage is a
+        first-crossing -- 'no prior' degrades gracefully to normal->action,
+        which broadcasts."""
+        evt = make_reading(value=9.2, flood_status="Action Stage",
+                            ts="2026-07-17T10:00:00-06:00")
+        event, gate = self._decide(adapter, evt)
+        assert event.category == "stream_high_water"
+        assert gate.broadcast is True
+        assert gate.lifecycle == "new"
+
+    def test_routine_reading_never_reaches_the_gate(self, adapter, mem_db):
+        """A below-action reading has no flood_status; the adapter drops it
+        before to_event() ever returns an Event (unchanged pre-fix behavior
+        -- this fix does not change what gets emitted, only what happens to
+        what was already being emitted)."""
+        evt = make_reading(value=5.0, flood_status=None,
+                            ts="2026-07-17T10:00:00-06:00")
+        assert adapter.to_event(evt) is None
+
+    def test_sustained_elevated_reading_suppresses(self, adapter, mem_db):
+        """Same site, same band, next tick: does NOT re-broadcast."""
+        first = make_reading(value=9.2, flood_status="Action Stage",
+                              ts="2026-07-17T10:00:00-06:00")
+        second = make_reading(value=9.3, flood_status="Action Stage",
+                               ts="2026-07-17T10:15:00-06:00")
+        _, gate1 = self._decide(adapter, first)
+        assert gate1.broadcast is True
+        _, gate2 = self._decide(adapter, second)
+        assert gate2.broadcast is False
+        assert "unchanged band" in gate2.reason
+
+    def test_escalation_broadcasts_again(self, adapter, mem_db):
+        """Action stage -> minor flood on the same site is a second, higher
+        crossing -- broadcasts again."""
+        action = make_reading(value=9.2, flood_status="Action Stage",
+                               ts="2026-07-17T10:00:00-06:00")
+        flood = make_reading(value=10.8, flood_status="Minor Flood",
+                              ts="2026-07-17T10:15:00-06:00")
+        _, gate1 = self._decide(adapter, action)
+        assert gate1.broadcast is True
+        event2, gate2 = self._decide(adapter, flood)
+        assert event2.category == "stream_flood_warning"
+        assert gate2.broadcast is True
+        assert gate2.lifecycle == "new"
+
+    def test_native_write_does_not_leak_into_central_source(self, adapter, mem_db):
+        """Sanity: the native persistence write in gating.hydro.decide() is
+        gated on source != 'nwis'. Calling decide() directly with
+        source='nwis' (the Central source) must NOT insert a row -- the
+        Central handler owns its own inline INSERT, and decide() must stay
+        read-only for that source (see hydro.py module docstring)."""
+        from meshai.notifications.gating.hydro import decide
+        canonical = {
+            "site_id": "USGS-99999999", "gauge_name": "Should Not Persist",
+            "stage_ft": 12.0, "flow_cfs": None, "unit": "ft",
+            "threshold_state": "action", "reading_time": 1_700_000_000,
+            "lat": 44.0, "lon": -115.0, "parameter_code": "00065",
+        }
+        decide(canonical, source="nwis", now=1_700_000_000.0)
+        row = mem_db.execute(
+            "SELECT COUNT(*) AS n FROM gauge_readings WHERE site_id=?",
+            ("USGS-99999999",),
+        ).fetchone()
+        assert row["n"] == 0
+
+
+# ─────────────────────────────────────────────────────────────────────────────
+# 3. Golden wire format — native event renders via the shared hydro formatter
+# ─────────────────────────────────────────────────────────────────────────────
+
+class TestFormatterGolden:
+    """Captured-from-current-behavior goldens for the native shape.
+
+    Unlike a Central envelope (which can carry a paired 00060 discharge value
+    via the 00060 back-look), a native reading NEVER carries flow_cfs -- see
+    to_event()'s docstring/comment: only stage/height readings reach
+    to_event() at all, so flow_cfs is always None here. The stage/label/coords
+    segments are otherwise identical to the Central-path golden in
+    test_hydro_refactor.py::TestFormatterGolden, since both flow through the
+    exact same formatters.hydro.format().
+    """
+
+    def _render(self, adapter, evt):
+        from meshai.notifications.gating import get_decider
+        from meshai.notifications.formatters.hydro import format as hfmt
+        from meshai.notifications import clock
+        event = adapter.to_event(evt)
+        decider = get_decider(event.category)
+        gate = decider(event.data, source=event.source, now=clock.now())
+        event.data.update(gate.data_patch)
+        return hfmt(event, now=clock.now(), budget=140)
+
+    def test_high_water_wire(self, adapter, mem_db):
+        evt = make_reading(
+            site_name="Snake River at Heise", value=9.2,
+            flood_status="Action Stage", ts="2026-07-17T10:00:00-06:00",
+            lat=43.612, lon=-111.654,
+        )
+        wire = self._render(adapter, evt)
+        assert wire == "🌊 New: Snake River at Heise: action stage 9.2 ft, @ 43.612,-111.654"
+
+    def test_flood_warning_wire(self, adapter, mem_db):
+        evt = make_reading(
+            site_name="Boise River", value=14.5,
+            flood_status="Minor Flood", ts="2026-07-17T10:00:00-06:00",
+            lat=43.600, lon=-116.200,
+        )
+        wire = self._render(adapter, evt)
+        assert wire == "🌊 New: Boise River: minor flooding 14.5 ft, @ 43.600,-116.200"
+
+    def test_major_flood_wire(self, adapter, mem_db):
+        evt = make_reading(
+            site_name="Test Gauge", value=20.0,
+            flood_status="Major Flood", ts="2026-07-17T10:00:00-06:00",
+            lat=44.0, lon=-114.0,
+        )
+        wire = self._render(adapter, evt)
+        assert wire == "🌊 New: Test Gauge: major flooding 20.0 ft, @ 44.000,-114.000"
+
+    def test_missing_coords_drops_at_tail(self, adapter, mem_db):
+        """Byte-identical drop behavior to the Central-path golden for the
+        same case (test_hydro_refactor.py::test_missing_coords_drops_at_tail)."""
+        evt = make_reading(
+            site_name="No Coords Gauge", value=10.0,
+            flood_status="Action Stage", ts="2026-07-17T10:00:00-06:00",
+            lat=None, lon=None,
+        )
+        assert adapter.to_event(evt) is None, "to_event() requires lat/lon"
+
+        # Exercise the formatter directly with coords stripped after the fact
+        # to prove the "@ ..." segment is correctly omitted, mirroring the
+        # Central golden (to_event() itself refuses a coord-less reading, so
+        # this checks the formatter behavior the same way
+        # test_hydro_refactor.py does: via a synthetic canonical dict).
+        from meshai.notifications.formatters.hydro import format as hfmt
+
+        class _FakeEvent:
+            pass
+        e = _FakeEvent()
+        e.data = {
+            "gauge_name": "No Coords Gauge", "threshold_state": "action",
+            "stage_ft": 10.0, "flow_cfs": None, "unit": "ft",
+            "lat": None, "lon": None,
+        }
+        wire = hfmt(e, now=1_700_000_000.0, budget=140)
+        assert_byte_identical(
+            wire, "🌊 New: No Coords Gauge: action stage 10.0 ft"
+        )
+        assert "@" not in wire
+
+
+# ─────────────────────────────────────────────────────────────────────────────
+# 4. End-to-end: compose_mesh_message renders the same wire (full pipeline)
+# ─────────────────────────────────────────────────────────────────────────────
+
+def test_compose_mesh_message_end_to_end(adapter, mem_db):
+    """Full pipeline: to_event() -> decider -> compose_mesh_message(), the
+    same call sequence store._emit_event() + the mesh dispatcher make in
+    production. Proves the NATIVE_ALWAYS_DECIDE gate actually takes effect
+    for compose_mesh_message's formatter dispatch, not just get_formatter()
+    resolution."""
+    from meshai.notifications.gating import get_decider
+    from meshai.notifications.renderers.composer import compose_mesh_message
+    from meshai.notifications import clock
+
+    evt = make_reading(
+        site_name="Snake River at Heise", value=9.2,
+        flood_status="Action Stage", ts="2026-07-17T10:00:00-06:00",
+        lat=43.612, lon=-111.654,
+    )
+    event = adapter.to_event(evt)
+    decider = get_decider(event.category)
+    gate = decider(event.data, source=event.source, now=clock.now())
+    assert gate.broadcast is True
+    event.data.update(gate.data_patch)
+    wire = compose_mesh_message(event)
+    assert wire == "🌊 New: Snake River at Heise: action stage 9.2 ft, @ 43.612,-111.654"