feat(3-K): real geocoder backends + producer-doc reframe + consumer-doc enrichment

Second of three PRs for v0.5.0 (J shipped the framework; this fills in real
backends + documents the reframed design principle in-tree; L is the events
tab + map fix, then tag).

Backends (all satisfy GeocoderBackend; never raise, all-null on any failure):
- NaviBackend — composed Navi /api/reverse/<lat>/<lon> (name/address + timezone
  + landclass + elevation in one call). Near-passthrough: response already
  matches the canonical 9-field shape. Best-effort warmup ping (Boise) on
  construction when a loop is running; config `headers` slot for a future
  Authorization: Bearer (config-only, no code change). Default base_url
  http://192.168.1.130:8440.
- PhotonBackend — raw Photon /reverse?lat&lon&limit=1 (name/address only).
  Maps features[0].properties; postal_code <- postcode; timezone/landclass/
  elevation_m null (Navi-composed-endpoint extras).
- NominatimBackend — OSM Nominatim /reverse?format=jsonv2 (name/address only).
  Configurable rate limit (default 1/sec; 0 disables for self-hosted) +
  required User-Agent. Maps the address block; landclass/elevation_m/timezone
  null.

Registered all three in supervisor _BACKEND_REGISTRY (resolved by EnrichmentConfig
backend_class name).

Docs — design pivot now in-tree:
- PRODUCER §2 reframed: the verbatim Matt quote stays; the translation inverts.
  Central is the consumer's only data plane (consumers can't do follow-up
  lookups), so enrich deliberately and centrally, namespaced under _enriched,
  failing to null. "No enrichment" is gone.
- PRODUCER §10.1 inverted: enrichment is expected; the anti-pattern is doing it
  OUTSIDE the framework (inline in poll(), bypassing cache + _enriched
  namespacing + the never-raise safety net).
- PRODUCER new §13 Enrichment contract: Enricher / GeocoderEnricher /
  GeocoderBackend Protocols, NoOpBackend default, sqlite cache + TTL +
  cache-all-null + don't-cache-on-raise semantics, _enriched.<name> provenance,
  per-field coverage matrix (cross-checked against GEOCODER_FIELDS), and the
  landclass antimeridian known wrinkle.
- CONSUMER FIRMS section: documents the data._enriched.geocoder bundle (9
  fields), per-region coverage (US-full, non-US timezone+elevation), and the
  antimeridian landclass caveat.

Tests:
- test_navi/photon/nominatim_backend.py — happy-path field mapping, null
  handling, extra-key drop, network/timeout/non-200/malformed -> all-null
  (never raises), Nominatim rate-limit (disabled + spacing) + User-Agent.
  Env-gated live Navi smoke (NAVI_INTEGRATION_TEST=1; skipped by default — the
  192.168.1.130 endpoint isn't reachable from CT104's segment).
- test_producer_doc.py — +4: §2 verbatim quote present, §10.1 subsection exists,
  §13 names all four protocol types, §13 coverage matrix == GEOCODER_FIELDS
  (derived from code, not hardcoded).

Verification: full pytest 525 passed, 1 skipped (was 495; +30 backend +
4 doc tests, -1 the env-gated skip). grep subject_for_event/_ADAPTER_REGISTRY
clean. All three backends import + resolve via the registry.

Flagged for later (NOT done here): adapters besides FIRMS that should declare
enrichment_locations (nwis, eonet, gdacs, usgs_quake, wfigs_*) — that's PR L
scope alongside the events tab. See PR description.

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

tests/test_navi_backend.py

@@ -0,0 +1,120 @@
+"""Tests for NaviBackend (composed Navi /api/reverse endpoint).
+
+HTTP is exercised via patching the backend's `_fetch` (the codebase has no
+aioresponses/respx dep); URL construction is asserted on the pure `_url`
+helper. An env-gated integration smoke against the live Navi endpoint is
+skipped by default.
+"""
+
+import os
+from unittest.mock import AsyncMock
+
+import pytest
+
+from central.enrichment.backends.navi import NaviBackend
+from central.enrichment.geocoder import GEOCODER_FIELDS, all_null_bundle
+
+# Full Navi response — already canonical shape.
+_NAVI_OK = {
+    "name": "Where you are",
+    "city": "Boise",
+    "county": "Ada",
+    "state": "Idaho",
+    "country": "United States",
+    "postal_code": "83702",
+    "timezone": "America/Boise",
+    "landclass": "Public — National Forest",
+    "elevation_m": 824,
+}
+
+
+def _backend() -> NaviBackend:
+    # warmup=False so construction issues no background task in tests.
+    return NaviBackend(base_url="http://navi.test:8440", warmup=False)
+
+
+def test_url_construction():
+    b = _backend()
+    assert b._url(43.615, -116.2023) == "http://navi.test:8440/api/reverse/43.615/-116.2023"
+
+
+def test_base_url_trailing_slash_stripped():
+    b = NaviBackend(base_url="http://navi.test:8440/", warmup=False)
+    assert b._url(1.0, 2.0) == "http://navi.test:8440/api/reverse/1.0/2.0"
+
+
+@pytest.mark.asyncio
+async def test_happy_path_passthrough():
+    b = _backend()
+    b._fetch = AsyncMock(return_value=dict(_NAVI_OK))
+    result = await b.reverse(43.615, -116.2023)
+    assert result == _NAVI_OK
+    assert set(result.keys()) == set(GEOCODER_FIELDS)
+
+
+@pytest.mark.asyncio
+async def test_partial_nulls_preserved():
+    """Navi 200-with-nulls (non-US: timezone + elevation, rest null)."""
+    partial = {**all_null_bundle(), "timezone": "Europe/Paris", "elevation_m": 35}
+    b = _backend()
+    b._fetch = AsyncMock(return_value=partial)
+    result = await b.reverse(48.85, 2.35)
+    assert result["timezone"] == "Europe/Paris"
+    assert result["elevation_m"] == 35
+    assert result["city"] is None
+    assert set(result.keys()) == set(GEOCODER_FIELDS)
+
+
+@pytest.mark.asyncio
+async def test_extra_keys_dropped():
+    b = _backend()
+    b._fetch = AsyncMock(return_value={**_NAVI_OK, "debug_internal": "leak"})
+    result = await b.reverse(1.0, 2.0)
+    assert "debug_internal" not in result
+    assert set(result.keys()) == set(GEOCODER_FIELDS)
+
+
+@pytest.mark.asyncio
+async def test_network_error_returns_all_null_never_raises():
+    b = _backend()
+    b._fetch = AsyncMock(side_effect=ConnectionError("boom"))
+    result = await b.reverse(1.0, 2.0)
+    assert result == all_null_bundle()
+
+
+@pytest.mark.asyncio
+async def test_timeout_returns_all_null():
+    import asyncio
+
+    b = _backend()
+    b._fetch = AsyncMock(side_effect=asyncio.TimeoutError())
+    assert await b.reverse(1.0, 2.0) == all_null_bundle()
+
+
+@pytest.mark.asyncio
+async def test_malformed_response_returns_all_null():
+    b = _backend()
+    b._fetch = AsyncMock(side_effect=ValueError("not json"))
+    assert await b.reverse(1.0, 2.0) == all_null_bundle()
+
+
+@pytest.mark.asyncio
+async def test_headers_passed_through_config():
+    b = NaviBackend(base_url="http://navi.test", headers={"Authorization": "Bearer x"}, warmup=False)
+    assert b._headers == {"Authorization": "Bearer x"}
+
+
+@pytest.mark.asyncio
+@pytest.mark.skipif(
+    os.environ.get("NAVI_INTEGRATION_TEST") != "1",
+    reason="set NAVI_INTEGRATION_TEST=1 to hit the live Navi endpoint",
+)
+async def test_live_navi_boise():
+    """Integration smoke against the real endpoint (default skipped)."""
+    b = NaviBackend(warmup=False)  # default base_url
+    result = await b.reverse(43.6150, -116.2023)
+    assert result["name"] == "Where you are"
+    assert result["city"] == "Boise"
+    assert result["state"] == "Idaho"
+    assert result["elevation_m"] is not None
+    assert abs(float(result["elevation_m"]) - 824) < 50