Initial font work

SHADER_CONTRACT.md

@@ -73,6 +73,7 @@ Optional fields:
 - `category`: UI grouping label.
 - `entryPoint`: Slang function to call. Defaults to `shadeVideo`.
 - `textures`: texture assets to load and expose as samplers.
+- `fonts`: packaged font assets for live text parameters.
 - `temporal`: history-buffer requirements.
 
 Shader-visible identifiers must be valid Slang-style identifiers:
@@ -80,6 +81,7 @@ Shader-visible identifiers must be valid Slang-style identifiers:
 - `entryPoint`
 - parameter `id`
 - texture `id`
+- font `id`
 
 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.
 
@@ -180,6 +182,7 @@ Supported types:
 | `color` | `float4` | `[r, g, b, a]` |
 | `bool` | `bool` | `true` or `false` |
 | `enum` | `int` | selected option index |
+| `text` | generated texture/helper | string |
 
 Float example:
 
@@ -278,12 +281,42 @@ else if (mode == 2)
 }
 ```
 
+Text example:
+
+```json
+{
+  "fonts": [
+    { "id": "inter", "path": "fonts/Inter-Regular.ttf" }
+  ],
+  "parameters": [
+    {
+      "id": "titleText",
+      "label": "Title",
+      "type": "text",
+      "default": "LIVE",
+      "font": "inter",
+      "maxLength": 64
+    }
+  ]
+}
+```
+
+Text parameters are runtime-owned strings. They are not emitted as uniform values. Instead, the runtime renders the current string into a single-line SDF mask texture and the shader wrapper exposes helpers based on the parameter id:
+
+```slang
+float mask = sampleTitleText(textUv);
+float4 premultipliedText = drawTitleText(textUv, float4(1.0, 1.0, 1.0, 1.0));
+```
+
+Text is currently limited to printable ASCII. `maxLength` defaults to `64` and is clamped to `1..256`. The optional `font` field references a packaged font declared in `fonts`; if no font is specified, the runtime uses its fallback sans-serif renderer.
+
 Parameter validation:
 
 - Float values are clamped to `min`/`max` if provided.
 - `vec2` must have exactly 2 numbers.
 - `color` must have exactly 4 numbers.
 - Enum defaults must match one of the declared option values.
+- Text defaults must be strings. Non-printable characters are dropped and values are clamped to `maxLength`.
 - Non-finite numeric values are rejected.
 
 ## Texture Assets
@@ -323,6 +356,31 @@ return float4(logo.rgb * alpha, alpha);
 
 See `shaders/dvd-bounce/` for a complete texture-driven example.
 
+## Font Assets
+
+Declare packaged font assets in the manifest:
+
+```json
+{
+  "fonts": [
+    {
+      "id": "inter",
+      "path": "fonts/Inter-Regular.ttf"
+    }
+  ]
+}
+```
+
+Rules:
+
+- `id` must be a valid shader identifier.
+- `path` is relative to the shader package directory.
+- The file must exist when the manifest is loaded.
+- Font asset changes trigger shader reload.
+- V1 text layout is single-line; shaders position and scale the generated text texture themselves.
+
+See `shaders/text-overlay/` for a complete live text example. The sample bundles Roboto Regular and includes its OFL license beside the font file.
+
 ## Temporal Shaders
 
 Temporal shaders can request access to previous frames.
@@ -401,6 +459,7 @@ These files are ignored by git and are useful for debugging compiler output. If
 - Do not write a `[shader("fragment")]` entry point in `shader.slang`; the runtime provides it.
 - Remember enum globals are integer indexes, not strings.
 - Declare every texture in `shader.json`; undeclared texture samplers will not be bound.
+- Declare packaged fonts in `shader.json` when text parameters should use a specific font.
 - Keep temporal history requests modest. They consume texture units and memory and are capped by runtime config.
 - If a parameter appears in the UI but not in Slang, the shader may still compile, but the control has no effect.
 - If a Slang name collides with a generated global, rename your parameter or local symbol.
@@ -414,6 +473,7 @@ Before committing a new shader package:
 - `entryPoint`, parameter IDs, and texture IDs are valid identifiers.
 - `shader.slang` implements the configured entry point.
 - Texture files referenced by `textures` exist.
+- Font files referenced by `fonts` exist.
 - Enum defaults are present in their `options`.
 - Temporal shaders handle short or empty history gracefully.
 - The app can reload and compile the shader without errors.