GPU culling

AGENTS.md

@@ -43,6 +43,7 @@ WGPU doesn't have a native "Context" object — this type groups them together f
 - wgpu 30.0.0 is pinned in `lib/Cargo.toml`. The comment says "check the latest version" — verify compatibility before upgrading.
 - No feature flags, no dev-dependencies, no tests yet. Adding any requires updating both `Cargo.toml` files if the dependency spans crates.
 - The workspace has no `[workspace.dependencies]` section. Dependencies are declared per-crate rather than centrally.
+- **WGSL `select` argument order** (cost us a day): `select(reject, accept, cond)` returns the **second** arg when `cond` is true — the reverse of HLSL's `select(trueVal, falseVal, cond)`. In `shaders/gpu_driven.wgsl` the cull pass must stay `select(0u, u32(flags.z), visible)` (visible ⇒ full count, culled ⇒ 0). Swapped args silently zero the counts of every visible entity → black window. See the GOTCHA comment at the top of that shader.
 
 <!-- lean-ctx -->
 ## lean-ctx