[mcp] Support MCP Apps part 3 - Add mcp tool call support. (#17364)

- [x] Add a new app-server method so that MCP Apps can call their own
MCP server directly.

codex-rs/app-server-protocol/schema/json/ClientRequest.json

@@ -1277,6 +1277,27 @@
       ],
       "type": "string"
     },
+    "McpServerToolCallParams": {
+      "properties": {
+        "_meta": true,
+        "arguments": true,
+        "server": {
+          "type": "string"
+        },
+        "threadId": {
+          "type": "string"
+        },
+        "tool": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "server",
+        "threadId",
+        "tool"
+      ],
+      "type": "object"
+    },
     "MergeStrategy": {
       "enum": [
         "replace",
@@ -4569,6 +4590,30 @@
       "title": "McpServer/resource/readRequest",
       "type": "object"
     },
+    {
+      "properties": {
+        "id": {
+          "$ref": "#/definitions/RequestId"
+        },
+        "method": {
+          "enum": [
+            "mcpServer/tool/call"
+          ],
+          "title": "McpServer/tool/callRequestMethod",
+          "type": "string"
+        },
+        "params": {
+          "$ref": "#/definitions/McpServerToolCallParams"
+        }
+      },
+      "required": [
+        "id",
+        "method",
+        "params"
+      ],
+      "title": "McpServer/tool/callRequest",
+      "type": "object"
+    },
     {
       "properties": {
         "id": {