fix: harden simulator data contracts

schemas/scene.schema.json

@@ -4,7 +4,7 @@
   "title": "micarrsim acoustic scene",
   "type": "object",
   "additionalProperties": false,
-  "required": ["schemaVersion", "kind", "id", "name", "units", "sampleRate", "duration", "speedOfSound", "seed", "sources"],
+  "required": ["schemaVersion", "kind", "id", "name", "units", "sampleRate", "duration", "speedOfSound", "seed", "mix", "sources"],
   "properties": {
     "schemaVersion": { "const": "1.0.0" }, "kind": { "const": "micarrsim.scene" },
     "id": { "type": "string", "pattern": "^[a-z0-9][a-z0-9._-]*$" },
@@ -14,6 +14,13 @@
     "duration": { "type": "number", "exclusiveMinimum": 0, "maximum": 300 },
     "speedOfSound": { "type": "number", "minimum": 250, "maximum": 400 },
     "seed": { "type": "integer", "minimum": 0, "maximum": 4294967295 },
+    "mix": {
+      "type": "object", "additionalProperties": false, "required": ["normalization", "targetPeak"],
+      "properties": {
+        "normalization": { "enum": ["none", "peak"] },
+        "targetPeak": { "type": "number", "exclusiveMinimum": 0, "maximum": 1 }
+      }
+    },
     "image": { "$ref": "#/$defs/image" },
     "assets": { "type": "array", "maxItems": 128, "items": { "$ref": "#/$defs/asset" } },
     "sources": { "type": "array", "minItems": 1, "maxItems": 32, "items": { "$ref": "#/$defs/source" } },