Root-caused via dat-truth inspection, not inference: the A7.L1 visible-
cell scoping fix (previous commit) had zero visual effect because the
Town Network fountain room (cell 0x00070144) registers ZERO lights of
its own — confirmed directly against the dat, not assumed. The room's
one dat-authored fixture, Setup 0x02000365 (a ceiling light 5m above the
fountain, warm color, intensity 100), has a single visual part that is a
#136-class runtime-hidden marker. Flattened mesh ref count: 0. GameWindow
's per-stab hydration loop treated meshRefs.Count==0 as "doesn't exist"
and dropped the whole entity before the Setup's Lights were ever read —
so a mesh-less "light attach point" fixture, a normal AC dat authoring
pattern, could never register. Retail's light registration (add_light,
CEnvCell::UnPack) is architecturally independent of a fixture's own mesh
visibility.
Fix: track the stab's Setup.Lights.Count alongside meshRefs during
hydration; keep the entity (with empty MeshRefs — nothing to draw, still
something to light) whenever either is nonzero. Extracted the decision
into EntityHydrationRules.ShouldKeepEntity (pure, unit-tested) since
GameWindow's hydration loop isn't independently testable. Confirmed no
downstream consumer assumes MeshRefs.Count >= 1 (WbDrawDispatcher already
guards on it before any indexing).
Core 2666+2skip / App 741+2skip / UI 425 / Net 385 green. Apparatus:
Issue93TownNetworkFountainRoomLightInspectionTests (dat-truth dump,
reusable for other rooms in this class).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
