docs(future): wgpu.f32 filetest texture-fixture deferment

docs/future/2026-07-16-wgpu-filetest-texture-fixtures.md

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+# wgpu.f32 filetest texture fixtures (deferred)
+
+## Status: deliberately deferred (2026-07-16, M6 P3 review)
+
+## What is deferred
+
+34 directives across the `texture/` filetest corpus carry
+`@unsupported(wgpu.f32)` with the rationale "texture fixtures are not
+bound through the GPU registry yet". The `wgpu.f32` probe target
+(lps-filetests `test_run/wgpu_probe.rs`) rejects any file with texture
+specs instead of binding its inline pixel fixtures.
+
+## Why
+
+The filetest fixture-binding path is written against **guest memory**:
+`alloc_shared()` places fixture pixels in the compiled shader's arena and
+the sampler uniform carries a real guest pointer. The wgpu backend has no
+guest memory — textures live in the backend registry
+(`GpuGraphics::create_texture` → `texture_uniform_value()` →
+`LpsValueF32::Texture2D`, resolved to a bind-group entry at render time).
+Supporting fixtures needs a parallel binding path, not an adaptation.
+
+Deferral was judged low-cost: GPU sampling semantics (wrap modes,
+`texelFetch` edge clamp, formats, filtering over `textureLoad`) are
+already pinned by the M5 gate — `lp-gfx-wgpu/tests/texture_corpus.rs` —
+so the filetest run would re-verify covered behavior through a second
+harness rather than add coverage. Nothing on the lp-gfx or Studio
+roadmaps consumes it.
+
+## What un-deferring takes (sm)
+
+1. Branch the harness fixture binding on the wgpu instance: create the
+   texture through the shared probe `GpuGraphics`, keep the
+   `TextureHandle` alive for the instance lifetime, take
+   `texture_uniform_value()`.
+2. Teach `WgpuProbeInstance`'s uniform-tree builder to carry
+   `Texture2D` values and dotted paths for struct-nested samplers
+   (`params.gradient`) — today it builds a flat tree and rejects dotted
+   `set_uniform` paths.
+3. Make `EXPECT_SETUP_FAILURE` files fail at bind time with matching
+   error text.
+4. Remove the 34 annotations (greppable by the rationale string) and
+   rerun `--target wgpu.f32`.
+
+Natural moment: fold into the assembly prototype-order fix (which removes
+~120 sibling annotations in the same motion).