refactor(protocol): separate wire validation schema in FunctionDefinition

Define a separate $defs/FunctionCallValidationSchema to explicitly validate client/server function calls on the wire, and compose it in $defs/FunctionDefinition alongside returnType/callableFrom metadata using allOf. This allows reusing validation constraints without leaking metadata parameters onto the wire protocol.

Author: gspencergoog

specification/v0_10/json/client_capabilities.json

@@ -25,12 +25,55 @@
   },
   "required": ["v0.10"],
   "$defs": {
+    "FunctionCallValidationSchema": {
+      "type": "object",
+      "description": "JSON Schema structure that validates a wire-level FunctionCall object.",
+      "properties": {
+        "type": {
+          "const": "object"
+        },
+        "description": {
+          "type": "string"
+        },
+        "properties": {
+          "type": "object",
+          "properties": {
+            "call": {
+              "type": "object",
+              "properties": {
+                "const": { "type": "string" }
+              },
+              "required": ["const"]
+            },
+            "args": {
+              "type": "object",
+              "description": "A JSON Schema describing the expected arguments (args) for this function.",
+              "$ref": "https://json-schema.org/draft/2020-12/schema"
+            }
+          },
+          "required": ["call"],
+          "additionalProperties": false
+        },
+        "required": {
+          "type": "array",
+          "items": { "type": "string" },
+          "contains": { "const": "call" }
+        },
+        "unevaluatedProperties": {
+          "type": "boolean"
+        },
+        "additionalProperties": {
+          "type": "boolean"
+        }
+      },
+      "required": ["type", "properties", "required"]
+    },
     "FunctionDefinition": {
       "type": "object",
       "description": "Describes a function's validation schema and interface metadata.",
       "allOf": [
         {
-          "$ref": "https://json-schema.org/draft/2020-12/schema"
+          "$ref": "#/$defs/FunctionCallValidationSchema"
         },
         {
           "type": "object",
@@ -49,7 +92,8 @@
           },
           "required": ["returnType"]
         }
-      ]
+      ],
+      "unevaluatedProperties": false
     },
     "Catalog": {
       "type": "object",