Add manifest support for pass declarations

SHADER_CONTRACT.md

@@ -97,6 +97,7 @@ Optional fields:
 - `description`: display/help text for the shader library.
 - `category`: UI grouping label.
 - `entryPoint`: Slang function to call. Defaults to `shadeVideo`.
+- `passes`: advanced render-pass declarations. Omit this for normal single-pass shaders.
 - `textures`: texture assets to load and expose as samplers.
 - `fonts`: packaged font assets for live text parameters.
 - `temporal`: history-buffer requirements.
@@ -110,6 +111,52 @@ Shader-visible identifiers must be valid Slang-style identifiers:
 
 Use letters, numbers, and underscores only, and start with a letter or underscore. For example, `logoTexture` is valid; `logo-texture` is not valid as a shader-visible texture ID.
 
+## Render Passes
+
+Most shaders should omit `passes`. The runtime then creates one implicit pass:
+
+```json
+{
+  "id": "main",
+  "source": "shader.slang",
+  "entryPoint": "shadeVideo",
+  "output": "layerOutput"
+}
+```
+
+Advanced shaders may declare explicit passes:
+
+```json
+{
+  "passes": [
+    {
+      "id": "blurX",
+      "source": "blur-x.slang",
+      "entryPoint": "blurHorizontal",
+      "inputs": ["layerInput"],
+      "output": "blurredX"
+    },
+    {
+      "id": "final",
+      "source": "final.slang",
+      "entryPoint": "finish",
+      "inputs": ["blurredX"],
+      "output": "layerOutput"
+    }
+  ]
+}
+```
+
+Pass fields:
+
+- `id`: required pass identifier. It must be a valid shader identifier and unique inside the package.
+- `source`: required Slang source path relative to the package directory.
+- `entryPoint`: optional Slang function for this pass. Defaults to the package-level `entryPoint`.
+- `inputs`: optional list of named inputs. Current reserved names include `layerInput` and future pass output names.
+- `output`: optional output name. Use `layerOutput` for the final visible layer result.
+
+Current runtime note: pass manifests are parsed and every declared pass is Slang-validated/compiled, but execution still uses the first pass until multipass render-target routing is enabled. Existing single-pass shaders are unaffected.
+
 ## Slang Entry Point
 
 Your shader file must implement the manifest `entryPoint`.