fix(client): Global rung derived its canvas from a pre-layout viewport

Eyeballed on Lendel: the Atlas opened on a Global map that was literally two
cells — one green, one blue — stretched across the window, reporting
19,598.512 km/gridunit, which is exactly half the body's circumference.

Two bugs, both of which the D-255 extent inversion turned from harmless into
fatal.

enter() fires its first request BEFORE this Control is laid out, and a
not-yet-laid-out size is not always exactly Vector2.ZERO — a few stray pixels
sailed past the `== Vector2.ZERO` guard, so the viewer asked for a 2x2
gridunit canvas and the server's 2:1 fit floored it to 2x1. That never
mattered while Global discarded the requested extent and took its cell counts
from the body's region grid; the moment the request became the canvas size, a
transient layout artefact became the map. Any viewport below a plausible
panel size is now treated as not-laid-out.

And Global was excluded from the refetch settle entirely, so a canvas born at
the wrong size could never heal however the window was resized. That
exclusion was correct when no viewport could change Global's extent. Global
now takes the SIZE refit like every other rung, but still never the pan
re-float — its canvas is whole-body and origin-anchored, and the server
ignores `center` for it.

Both have regression tests. The second asserts on _world_center rather than
_view_offset, because _recompute_canvas_transform() legitimately re-centres
the offset on any canvas adoption and would have made the test pass for the
wrong reason.

Worth noting for the class: no test written today could have caught this.
Every one supplies an explicit viewport. The bug lived entirely in the gap
between "scene loads" and "layout completes" — a seam a live launch
exercises and a unit test does not.

Also stages governance/README.md's pql-maintained record index (D-258).

Pair session with Jeroen, 2026-07-26.

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

governance/README.md

@@ -323,6 +323,7 @@ line in place — keep the Q-record for the audit trail rather than deleting it.
 - [D-255: Body Map Viewer — stepped Atlas render architecture (supersedes the T-1143 continuous-ladder mechanism)](decisions/architecture.md#d-255-body-map-viewer--stepped-atlas-render-architecture-supersedes-the-t-1143-continuous-ladder-mechanism) — _architecture_
 - [D-256: Canonical sampling convention — one absolute-metre derive core; the batch layer is a survey raster](decisions/architecture.md#d-256-canonical-sampling-convention--one-absolute-metre-derive-core-the-batch-layer-is-a-survey-raster) — _architecture_
 - [D-257: Environment props share the character toon shading treatment; minimal-PBR carve-out for glazing](decisions/architecture.md#d-257-environment-props-share-the-character-toon-shading-treatment-minimal-pbr-carve-out-for-glazing) — _architecture_
+- [D-258: Rung-0.5 expanded layer — one derived base for the whole ladder](decisions/architecture.md#d-258-rung-05-expanded-layer--one-derived-base-for-the-whole-ladder) — _architecture_
 
 ## Open questions