fix(shaders): deduplicate VertexOutput/vs_main via render/fullscreen_uv_vs snippet

- Fix vs_main return type (VertexOutput, not vec4<f32>)
- Fix #include paths in passthrough, gaussian_blur, heptagon, combined_postprocess
- ShaderComposer: assert + suggest correct path on missing #include (non-STRIP_ALL)
- VerifyIncludes: upgrade WARNING to ERROR + assert, add "did you mean?" hint

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/common/shaders/render/fullscreen_uv_vs.wgsl b/common/shaders/render/fullscreen_uv_vs.wgsl
new file mode 100644
index 0000000..42d87c3
--- /dev/null
+++ b/common/shaders/render/fullscreen_uv_vs.wgsl
@@ -0,0 +1,15 @@
+// Common vertex shader for fullscreen post-processing effects.
+// Draws a single triangle that covers the entire screen, with uv
+// coordinates in [0..1]
+struct VertexOutput {
+    @builtin(position) position: vec4<f32>,
+    @location(0) uv: vec2<f32>,
+};
+
+@vertex fn vs_main(@builtin(vertex_index) i: u32) -> VertexOutput {
+    let pos = array<vec4f, 3>(vec4f(-1, -1, 0, 1.), vec4f(3, -1, 2., 1.), vec4f(-1, 3, 0, -1));
+    var out: VertexOutput;
+    out.position = vec4f(pos[i].xy, 0.0, 1.0);
+    out.uv = pos[i].zw;
+    return out;
+}