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SHADER_CONTRACT.md

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+# Shader Package Contract
+
+Each shader package lives under `shaders/<id>/` and includes:
+
+- `shader.json`
+- `shader.slang`
+
+## Manifest fields
+
+`shader.json` defines:
+
+- `id`
+- `name`
+- `description`
+- `category`
+- `entryPoint`
+- `parameters`
+
+Supported parameter types:
+
+- `float`
+- `vec2`
+- `color`
+- `bool`
+- `enum`
+
+## Slang contract
+
+The runtime owns the fragment entry point, video decode, and final mix/bypass behavior.
+
+Your `shader.slang` file implements:
+
+```slang
+float4 shadeVideo(ShaderContext context)
+{
+    return context.sourceColor;
+}
+```
+
+Available built-ins through `ShaderContext`:
+
+- `uv`
+- `sourceColor`
+- `inputResolution`
+- `outputResolution`
+- `time`
+- `frameCount`
+- `mixAmount`
+- `bypass`
+
+Manifest parameters are exposed to the shader as globals named by their `id`.
+
+Helper function:
+
+- `sampleVideo(float2 uv)` returns decoded RGBA video from the live DeckLink input.