feat(geo): vector tiles of features for maps

[nossila]

Summary

Vector tiles for baseapp.geo, to fold into #445. Maps can now draw every feature at every zoom; the geoFeatures connection returns at most 100 per page.

• Endpoint: GET /v1/geo/tiles/{z}/{x}/{y}.mvt serves GeoJSONFeatures as Mapbox Vector Tiles built by PostGIS (ST_TileEnvelope, ST_AsMVTGeom, ST_AsMVT). No new runtime dependency.
• First REST surface of the package: baseapp/geo/rest_framework/ (views.py, urls.py, permissions.py), wired through GeoPlugin.v1_urlpatterns in the staticmethod form.

Behavior

• Zoom ≥ cluster_max_zoom (13): a features layer with every feature in the tile. Points stay points and polygons stay polygons, clipped to the tile plus a 64px buffer. Attributes are id and feature_type.
• Below it: a clusters layer. Each tile is split into a cluster_grid_size² (16×16) grid; each non-empty cell becomes a point at the centroid of its features, with point_count.
  • Polygons count by ST_PointOnSurface.
  • Tile bounds are half-open, so each feature is counted in exactly one tile and totals add up.
• Filters: the same query parameters as geoFeatures, by reusing GeoJSONFeatureFilter as-is (feature_type, target_object_id, bbox, near). No new filter API.
• Errors: the filters raise Django ValidationErrors while the queryset is evaluated, after is_valid(). The view catches them and returns 400 with field errors instead of a 500. test_filterset_raises_validation_error_outside_graphene is untouched.
• Access: CanViewGeoJSONFeatures calls request.user.has_perm("<app>.view_geojsonfeature"), so a project that overrides GeoPermissionsBackend gets the same rule on tiles as on GraphQL.
• Responses: 204 for empty tiles and 404 for out-of-range tiles. Cache-Control: public, max-age=300, so a CDN can absorb map pans.

SQL

• The geography column is cast to geometry before ST_Transform(…, 3857).
• From zoom 4, a geography __intersects prefilter runs on the tile envelope padded by 10%. It uses the GiST index, which I verified exists: sqlmigrate geo 0001 creates geo_geojsonfeature_geometry_…_id USING GIST ("geometry"). Then an exact planar test in EPSG:3857.
• Tiles below zoom 4 skip the prefilter: on tiles that large, the geography envelope's great-circle edges diverge from the Mercator edges.
• Property expressions are aliased internally (_mvt_property_N) and renamed in the outer query, since Django rejects annotations named like model fields (e.g. id).

Extension points

• Hooks: get_queryset, filter_queryset, get_feature_properties (ORM expressions become MVT attributes).
• Settings: cluster_max_zoom, cluster_grid_size, layer names and cache_max_age.
• baseapp.geo.tiles.build_features_tile / build_clusters_tile build tiles from any queryset, for custom endpoints.
• The README has a section with a MapLibre example and a subclass example.

Tests

• baseapp/geo/tests/test_rest_tiles.py, 15 tests on real PostGIS, no mocks. They cover tile math, points and polygons, the properties hook, cluster aggregation, the polygon cluster, counts across a tile edge, 204/404, cache headers, filter pass-through, 400 for malformed filters, and permission via has_perm.
• Tiles are decoded by baseapp/geo/tests/mvt.py, a small protobuf-free MVT decoder. mapbox-vector-tile was the first choice, but it requires protobuf<7. Locking it downgraded protobuf from 7.36 to 6.33 for every consumer of the library, which is too much for a test helper.

Test plan

• pytest baseapp/geo/tests/: 105 passed. baseapp/geo coverage is 99% (tiles.py 100%, rest_framework/views.py 95%).
• black, isort, flake8 and ast-grep are clean on the changed files.
• Consumer check: the whatplant map switches to these tiles in a follow-up there (thousands of occurrences per city).

🤖 Generated with Claude Code

https://claude.ai/code/session_019P1oyApi4BLS8iLfMEGm8b

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