R1 measured first: a capped Region tile through the real production path
(build_district_window_layer + T-1151 par_iter) at the 64x64 wire cap
costs 0.40-0.48ms — faster than the shipped district n=64 window, so
Jeroen's progressive capped-density tiling ruling is comfortably
interactive on-demand. Raw orbital derive ~0.9µs/cell (~2.3x faster than
full derive; region_baseline dominates, not invent_primitives).
R5 redesign: WindowGranularity enum (Quarter/District/Region), serde
named-variant per the RoadNodeKind precedent, spacing from D-243 scale::
constants — the single source of truth. Additive serde-default
window_granularity_v2 request field (None = legacy u32 path; v2 wins when
Some); DistrictWindowLayer.granularity_v2 always echoed. Legacy u32 echo
for Region uses reserved WINDOW_GRANULARITY_REGION_KEY = u32::MAX (never
a legal input) so the old slot cannot lie about aliasing. Cache and
coalescing keys carry the enum itself (Ord by declaration order, D-010).
n stays district-extent at every rung; Region's cell grid is a DIVISION
(round(n/100), min 1) with its own per-axis ceiling
DISTRICT_WINDOW_MAX_N_REGION=6400 and a bounded halving-loop clamp (no
closed form under the rounding division — the client mirror must
replicate the loop).
derive_orbital_at_metres: bilinear envelope reads + region_baseline
temperature, NO invent_primitives (proven by test — slope_q pinned 0),
routed through the shared build_district_profile classification tail so
the existing colorizer family renders orbital cells unchanged. R2
stepped-categorical behavior documented at the function, not implied.
Region aliasing + clamp/echo tests mirror the T-1150 discipline. 1813
lib tests green; clippy clean; fixture regenerated (254->278 bytes, new
echoed field).
Extract derive_district's fractional-metres interior into the metres-
addressable derive_at_metres(seed, body, params, ta, wx, wy, climate,
min_wavelength_m) — the zoom ladder's keystone (design doc §8 step 1).
derive_district is now a thin DistrictPos-quantizing wrapper calling it
with cutoff 0.0; all four golden/believability/derivation harnesses pass
byte-identical.
enveloped_fbm/terrain_detail/voxel_relief gain min_wavelength_m: octaves
below the cutoff are hard-truncated (amp still advances so surviving
octaves keep relative weight; norm==0 guarded). Amplitude-fade-near-
cutoff is documented as a seam, not built — the pop-risk A/B needs the
client ladder (T-1153). Cutoff 0.0 is bit-identical to pre-change
output, asserted by test.
Measured (release, 4096-cell sweeps, zoom_ladder_bench.rs): district
spacing 1.200µs/cell (cutoff 0) / 1.201µs (cutoff 2048m — all octaves
survive, plumbing check); quarter spacing 1.165µs/cell (cutoff 512m).
Matches the design doc's ~1.2-1.4µs/cell release estimate.
jpmschweitzer