Added trigger

SHADER_CONTRACT.md

@@ -187,6 +187,7 @@ Supported types:
 | `bool` | `bool` | `true` or `false` |
 | `enum` | `int` | selected option index |
 | `text` | generated texture/helper | string |
+| `trigger` | `int <id>`, `float <id>Time` | pulse/count |
 
 Float example:
 
@@ -314,6 +315,26 @@ 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.
 
+Trigger example:
+
+```json
+{
+  "id": "flash",
+  "label": "Flash",
+  "type": "trigger"
+}
+```
+
+A trigger appears as a button in the control UI. Pressing it increments the shader-visible integer `flash` and records the runtime time in `flashTime`:
+
+```slang
+float age = context.time - flashTime;
+float intensity = flash > 0 ? exp(-age * 5.0) : 0.0;
+color.rgb += intensity;
+```
+
+Triggers are useful for one-shot shader reactions such as flashes, ripples, cuts, or randomized looks. They do not execute arbitrary CPU code; they only update uniforms consumed by the shader.
+
 Parameter validation:
 
 - Float values are clamped to `min`/`max` if provided.
@@ -321,6 +342,7 @@ Parameter validation:
 - `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`.
+- Trigger values are incremented by the host when triggered. The shader sees the trigger count and last trigger time.
 - Non-finite numeric values are rejected.
 
 ## Texture Assets