feat(client): size the Global rung to the viewport, not the region grid

Global took its cell counts from `global_cell_counts()` — one gridunit per
region — and discarded the requested extent entirely. On GJ380c that produced
a 191x95 canvas built from a heightmap stored at 512x256: roughly seven times
the available cells thrown away before anything was drawn. The count also
shrank as REGION_M grew, so tuning the scale ladder silently degraded the
opener, which is why the top of the ladder got worse rather than better as
the ladder itself was refined.

Global now fits the largest 2:1 canvas inside the requested extent. It cannot
take its ASPECT from the viewport — the canvas is equirectangular whole-body,
360 degrees of longitude by 180 of latitude, and must stay 2:1 or the cells
stop being square and the map shears — so the existing letterbox absorbs the
remainder. A hostile extent is still clamped; sizing to the request is not
trusting the request.

Global also joins the deep display ratio, making the band uniform. At 5 px
per gridunit a 1920 px window asked for 384 cells across a body whose
heightmap holds 512x256 — discarding stored detail to save work already done.
At 2 px it asks for 960, which is heightmap-native: nothing thrown away,
nothing invented, and the same screen area filled either way.

A body with no radius is not a sphere (asteroid belt, oort cloud) and has no
equirectangular surface to fit. Those degrade to the region grid — a visibly
degenerate 1x1 canvas — rather than a plausible-looking lie at whatever size
the viewport happened to ask for.

project.yaml 0.4.3 -> 0.4.4 invalidates the persisted step-canvas disk cache.
District/Quarter/Block/Chunk kept identical 960x540 cell counts through the
extent inversion, so their cache keys are byte-identical while a District
canvas now covers 3.6 km of ground instead of 1,966 km — a warm cache would
silently serve pre-inversion canvases.

Global still rides the orbital derive, so it carries no courses yet; that is
the next step and is deliberately separate, being a cost question over the
whole body rather than a sizing one.

Pair session with Jeroen, 2026-07-26.

Co-Authored-By: Claude <noreply@anthropic.com>

project.yaml

@@ -8,7 +8,13 @@ name: The Settled Reach
 # position raw (no coast_warp_px) — T-1160 applies the warp at orbital
 # sampling, changing orbital-rung canvas bytes (elev_q/temperature_dc/
 # moisture_q shift near coasts) — 0.4.3 forces those cached entries to miss.
-version: 0.4.3
+# 0.4.3-tagged canvases predate the D-255 extent inversion (a rung now fixes
+# the canvas EXTENT and the gridunit spacing falls out, rather than the
+# reverse). District/Quarter/Block/Chunk kept the same 960x540 cell counts
+# through that change, so their cache keys are byte-identical while a District
+# canvas now covers 3.6 km of ground instead of 1,966 km — a warm cache would
+# silently serve pre-inversion canvases. 0.4.4 forces those entries to miss.
+version: 0.4.4
 repository: settled-reach