docs: what the quality tracks left open — boot, the 2.3% margin, and the draw-call ceiling

TODO.md

@@ -934,3 +934,60 @@ which was one number for a board that is no longer looked at from one distance.
   buffers got *smaller* — 59,166 instances to 19,000 — so this is boot and
   memory, not frame time. Building the fine rungs lazily, on the first pose that
   asks for one, would move most of it off the boot path.
+
+## What the ground and lot work left open
+
+Recorded 2026-08-24 after both tracks landed, from the integration analysis that
+built the actual combination rather than adding up two reports.
+
+**The board boots a second slower, and nobody has signed that off.** Measured,
+three interleaved runs each, navigation to `boot.hidden === true`:
+
+| build | boot | heap |
+| --- | --- | --- |
+| before both tracks | 1,994 / 1,998 / 2,341 ms | 36-37 MB |
+| ground only | 2,029 / 2,048 / 2,260 ms | 36-38 MB |
+| lots only | 2,932 / 3,003 / 3,238 ms | 47-49 MB |
+| both | 3,011 / 3,079 / 3,368 ms | 48-49 MB |
+
+The ground material's texture build is confirmed negligible — ground-only is
+base. The whole of it is `createBlocks` walking every district once per rung of
+the lot ladder it can reach. **The rungs should be built lazily**: a rung nothing
+has asked for is a rung nobody has paid for, and the coarse-fill already means a
+district can be missing a rung without breaking a frame. This is the single
+biggest thing left on the merged board's boot.
+
+**Triangle headroom at the worst pose is 2.3%, and it is held by one constant.**
+`LOT_BUDGET = 19_000` bounds the *city* at 190,000 triangles. It does not bound
+the frame, because the non-city cost — terrain, corridor, sky, ports, vessels —
+is measured and not enforced, and it reaches 288,365 at LA from 110 km. The worst
+combined pose anywhere in either metro's descent is 390,730 at LA 10.5-11.5 km.
+`california-one-basin` now stands there, so CI will notice; but the next piece of
+work that adds geometry anywhere on this board inherits **9,270 triangles** of
+room at that pose, not the 184,000 that SF at 2.5 km suggests.
+
+**Draw calls are effectively gone: 438 of 460 desktop, 434 of 455 mobile.** The
+terrain chunk grid spent 17 and neither quality track spent any. Everything in
+`CALIFORNIA.md` that adds an object — an airport, a port, a landmark group — is
+now constrained by this and not by triangles. The content programme's own note
+says draw calls are the scarce resource; they are scarcer than it says. Airports
+and ports will have to batch into the existing material roles, or be gated by
+stand-off the way metro detail already is.
+
+**Los Angeles at 7.7 km looks coarser than it did**, because the ladder chose a
+250 m rung to bring that pose from 621,866 under the cap. That is a real
+trade — legality bought with appearance — and it is the correct one while the
+alternative is a board 55% over its budget. It gets better when the boot cost
+above is fixed and the budget can be spent where it is seen.
+
+Two smaller things, both disclosed by their own tracks and neither blocking:
+
+- **The ground grain reads a little like stucco at a close pose over flat
+  ground.** It is isotropic fbm; real terrain has drainage, and an isotropic
+  noise field cannot express a watershed. A flow-aligned or ridged term would,
+  and would cost nothing extra to sample.
+- **The Sierra escarpment's vertical striping is pre-existing and unfixed.** It
+  is the 15x exaggeration turning 300 m terrain cells into near-vertical ribs.
+  The detail map's slope correction correctly declines to add grain on top of it,
+  which is why it neither helps nor hurts. The fix is finer cells there, which is
+  terrain level of detail — the piece that still does not exist.