Real weather, real aircraft, a heightfield off the main thread, and instruments

Three things that were built and never connected, connected.

**The weather was already there.** `observe()` has always taken a
`WeatherObservation` and `main.ts` has always passed null, so the cloud,
precipitation, visibility and marine-layer paths in atmosphere.ts had never run
outside a test. The server already shipped NWS, met.no and Open-Meteo, all
configured off. What was actually missing was that a single TERA_ORIGIN_LAT/LNG
served one metro and lied to the other — so weather and traffic are per-region
now, derived from the city's own bounds, and the Bay Area gets its fog while
Long Beach gets its own sky. The route takes ?city= or a validated ?lat=&lng=
and refuses to become an open geocoding proxy for the planet.

**The heightfield moved to a Worker.** 2.3 s of blocked main thread at boot, and
another ~950 ms of point-in-polygon on top of it: the park mask is filled in the
worker now, and block placement samples four corners and only runs the exact
test on a cell that straddles an edge — 8 buildings differ out of 185,036.
createScene is async and takes a Stage as a consequence, and there is a
main-thread fallback because "clone it and it works" has no exception clause.

**Spaces is a chunk you fetch when you reach for the door**, not one everybody
downloads. Same for the godmode tools. The entry chunk is 722 kB rather than
772; three.js is most of what is left and splitting it is a different job.

**Godmode is an instrument panel now** rather than one slider: the date and the
season, not just the hour, so the Meeus moon and the sun's seasonal arc become
visible instead of merely correct; a weather override that says on screen when
it is lying; a frame-time and draw-call readout; and a pose editor that emits a
paste-ready Chapter block, which is the thing that makes adding New York cheap.

Two blockers the review caught:

  - Every city switch leaked 8 GPU textures — one of them a 2048x2048 shadow map
    — and ~10.5 shader programs, and deleteTexture had never been called once in
    the app's lifetime. The renderer was being built per scene; it belongs to the
    canvas, for the life of the page.
  - An upstream fetch that threw rather than returning null skipped the cache
    stamp, so the TTL — the only rate limit on outbound calls — collapsed to one
    upstream request per inbound request, and the caller got a 500.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/engine/blocks.ts

@@ -131,8 +131,26 @@ export function createBlocks(world: World): THREE.InstancedMesh {
 
         const [lat, lng] = world.unproject(x, z);
         if (!world.pointInPolygon(lat, lng, district.polygon)) continue;
-        if (!world.isLand(lat, lng)) continue;
-        if (world.pointInAny(lat, lng, world.city.parks)) continue;
+        /**
+         * Land and parks come off the lattice; the district polygon does not.
+         *
+         * The three tests used to be three exhaustive polygon walks each, and
+         * on the Bay Area's 186k candidate lots that was 240 ms of the boot's
+         * main thread — the largest single item in it, spent re-deriving what
+         * the heightfield Worker had already worked out for the whole board.
+         * `isLandSampled` and `inParkSampled` read that answer and fall through
+         * to the exact test only on a lattice cell that straddles the edge, so
+         * the coastline and the park boundaries are still decided by the
+         * polygons; see `World.sampled`. Same 186k lots, 19 ms.
+         *
+         * The district stays exact because there is no mask for it: districts
+         * are not a property of the lattice, they overlap, and San Francisco
+         * declares fifty-two of them. It is also the cheap one — the polygons
+         * are a dozen vertices and the bounding box rejects almost everything,
+         * which is 47 ms against the coastline's 235.
+         */
+        if (!world.isLandSampled(lat, lng)) continue;
+        if (world.inParkSampled(lat, lng)) continue;
         if (rand() > coverage) continue; // yards, car parks, the unbuilt lots
 
         // Cubed, so tall buildings stay rare and the skyline keeps a