feat(notifications): Phase 2.9 usgs water adapter pipeline integration

Adds USGSStreamsAdapter.to_event(), wiring the USGS Water Services stream
gauge adapter into the notification EventBus, following the Phase 2.7
traffic pattern.

to_event() design (emit only actionable/elevated readings):
- Category from flood_status: an exceeded stage (Minor/Moderate/Major
  Flood) -> stream_flood_warning; "Action Stage" (approaching) ->
  stream_high_water.
- A routine reading has no flood_status and is intentionally NOT emitted
  (returns None) -- the two categories are both flood-specific and routine
  gauge chatter is not actionable. This matches the spec ("category ...
  based on flood_status").
- Severity: passed through unchanged from the adapter's NWPS-stage logic
  (action->routine, minor/moderate->priority, major->immediate).
- Summary: reading value/unit + flood status.
- group_key/inhibit_keys: a single stable {site_id}_{param} key (the
  adapter's own event_id) as both. Re-polls coalesce; severity tiering is
  delegated to the pipeline Inhibitor (no severity encoded in the key).
- Defensive: missing lat/lon or event_id returns None; try/except-guarded.

store fix (meshai/env/store.py): _emit_event now skips a None return from
to_event() instead of passing it to bus.emit(). Required because usgs
returns None for the common (routine) reading; also retroactively protects
the defensive None returns of the FIRMS/traffic/roads511 adapters, which
previously would have logged a spurious "Failed to emit" warning.

Rule 17: no new tunable. usgs sites / tick_seconds / flood_thresholds
already exist in env_feeds.yaml (GUI-editable). Open API, no key, no .env
entry. Rule 16: standalone path validated end-to-end below.

Tests: tests/test_adapter_usgs.py (13 tests) mirrors test_adapter_traffic
-- category split (flood vs action), severity pass-through,
group_key/inhibit_keys, field population, and the non-emit/defensive cases
(routine -> None, missing lat/lon -> None, missing event_id -> None,
missing properties -> None, corrupted -> None). Full suite: 174 passed.

Live smoke test (prod, sites 13090500 Snake R nr Twin Falls, 13092747 Rock
Creek at Twin Falls, 13108150 Salmon Falls Creek nr Hagerman): clean
startup, 7 env adapters loaded, no traceback. "USGS streams updated: 6
readings from 3 sites" with NWPS flood stages resolved for all 3 -- fetch
succeeds over the open API with no DNS/auth errors (Phase 2.6.6 DNS fix).
All gauges currently below action stage, so flood_status is None and
to_event correctly emits nothing; the new None-guard skipped all 6 with no
error log. The emission path (elevated -> stream_flood_warning /
stream_high_water) is unit-validated and is the same store->bus path
emitting live for NWS (weather_warning/statement) and traffic
(traffic_congestion).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_adapter_usgs.py

@@ -0,0 +1,193 @@
+"""Tests for USGS water adapter Phase 2.9 — to_event() method."""
+
+import time
+from unittest.mock import MagicMock
+
+import pytest
+
+from meshai.env.usgs import USGSStreamsAdapter
+from meshai.notifications.events import Event
+
+
+# ============================================================
+# FIXTURES
+# ============================================================
+
+@pytest.fixture
+def mock_config():
+    """Create a mock USGSConfig with real scalar fields."""
+    config = MagicMock()
+    config.sites = []
+    config.tick_seconds = 900
+    config.flood_thresholds = {}
+    return config
+
+
+@pytest.fixture
+def adapter(mock_config):
+    """Create a USGSStreamsAdapter with mocked config."""
+    return USGSStreamsAdapter(mock_config)
+
+
+def make_usgs_event(
+    site_id="13090500",
+    param_type="height",
+    site_name="SNAKE RIVER NR TWIN FALLS ID",
+    severity="priority",
+    flood_status="Minor Flood",
+    value=10.8,
+    unit="ft",
+    lat=42.6,
+    lon=-114.47,
+    headline=None,
+):
+    """Helper to create a stored USGS event dict (mirrors _fetch)."""
+    now = time.time()
+    if headline is None:
+        headline = f"{site_name}: {value} {unit}"
+        if flood_status:
+            headline += f" — {flood_status}"
+    return {
+        "source": "usgs",
+        "event_id": f"{site_id}_{param_type}",
+        "event_type": "Stream Gauge",
+        "headline": headline,
+        "severity": severity,
+        "lat": lat,
+        "lon": lon,
+        "expires": now + 1800,
+        "fetched_at": now,
+        "properties": {
+            "site_id": site_id,
+            "site_name": site_name,
+            "parameter": "Gage height" if param_type == "height" else "Streamflow",
+            "value": value,
+            "unit": unit,
+            "timestamp": "2026-05-27T12:00:00",
+            "flood_status": flood_status,
+            "flood_stages": {"action_stage": 9.0, "flood_stage": 10.5},
+        },
+    }
+
+
+# ============================================================
+# CATEGORY TESTS
+# ============================================================
+
+def test_minor_flood_is_flood_warning(adapter):
+    """Minor/Moderate/Major flood maps to stream_flood_warning."""
+    for status in ["Minor Flood", "Moderate Flood", "Major Flood"]:
+        event = adapter.to_event(make_usgs_event(flood_status=status))
+        assert event is not None
+        assert event.category == "stream_flood_warning"
+
+
+def test_action_stage_is_high_water(adapter):
+    """Action Stage maps to stream_high_water."""
+    event = adapter.to_event(make_usgs_event(flood_status="Action Stage", severity="routine"))
+    assert event is not None
+    assert event.category == "stream_high_water"
+
+
+# ============================================================
+# SEVERITY PASS-THROUGH TESTS
+# ============================================================
+
+def test_severity_passes_through(adapter):
+    """Severity from the stored event passes through unchanged."""
+    for sev in ["routine", "priority", "immediate"]:
+        event = adapter.to_event(make_usgs_event(severity=sev, flood_status="Minor Flood"))
+        assert event is not None
+        assert event.severity == sev
+
+
+# ============================================================
+# GROUP KEY / INHIBIT KEY TESTS
+# ============================================================
+
+def test_group_key_is_site_param(adapter):
+    """Group key is the stable {site_id}_{param} key."""
+    event = adapter.to_event(make_usgs_event(site_id="13090500", param_type="height"))
+    assert event is not None
+    assert event.group_key == "13090500_height"
+
+
+def test_inhibit_keys_match_group_key(adapter):
+    """The sole inhibit key equals the group key (Inhibitor does severity tiering)."""
+    event = adapter.to_event(make_usgs_event())
+    assert event is not None
+    assert event.inhibit_keys == [event.group_key]
+
+
+def test_flow_and_height_distinct_keys(adapter):
+    """Flow and height for the same site get distinct group keys."""
+    e_h = adapter.to_event(make_usgs_event(param_type="height"))
+    e_f = adapter.to_event(make_usgs_event(param_type="flow"))
+    assert e_h.group_key != e_f.group_key
+
+
+# ============================================================
+# CONTENT / FIELD POPULATION TESTS
+# ============================================================
+
+def test_populates_core_fields(adapter):
+    """Core Event fields are populated from the stored dict."""
+    evt = make_usgs_event(lat=42.61, lon=-114.48)
+    event = adapter.to_event(evt)
+    assert event is not None
+    assert event.source == "usgs"
+    assert event.lat == 42.61
+    assert event.lon == -114.48
+    assert event.expires == evt["expires"]
+    assert event.timestamp == evt["fetched_at"]
+    assert event.id  # auto-computed
+
+
+def test_summary_includes_value_and_status(adapter):
+    """Summary includes the reading value and flood status."""
+    event = adapter.to_event(make_usgs_event(value=11.2, unit="ft", flood_status="Moderate Flood"))
+    assert event is not None
+    assert "11.2 ft" in event.summary
+    assert "Moderate Flood" in event.summary
+
+
+# ============================================================
+# DEFENSIVE / NON-EMIT TESTS
+# ============================================================
+
+def test_routine_reading_returns_none(adapter):
+    """A routine reading (no flood_status) is not emitted."""
+    assert adapter.to_event(make_usgs_event(flood_status=None, severity="routine")) is None
+
+
+def test_missing_coords_returns_none(adapter):
+    """Missing coordinates returns None."""
+    evt = make_usgs_event()
+    evt["lat"] = None
+    assert adapter.to_event(evt) is None
+
+
+def test_missing_event_id_returns_none(adapter):
+    """Missing event_id returns None (no stable group key)."""
+    evt = make_usgs_event()
+    evt["event_id"] = None
+    assert adapter.to_event(evt) is None
+
+
+def test_missing_properties_returns_none(adapter):
+    """No properties dict means no flood_status, so no emit."""
+    evt = {
+        "source": "usgs",
+        "event_id": "13090500_height",
+        "severity": "routine",
+        "headline": "x",
+        "lat": 42.6,
+        "lon": -114.47,
+        "fetched_at": time.time(),
+    }
+    assert adapter.to_event(evt) is None
+
+
+def test_does_not_raise_on_corrupted_dict(adapter):
+    """Corrupted dict returns None without raising."""
+    assert adapter.to_event({"garbage": True}) is None