Fix generated C# leading underscore names

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: stephentoub

dotnet/src/Generated/Rpc.cs

@@ -209,6 +209,38 @@ describe("session event codegen", () => {
         );
     });
 
+    it("drops leading underscores from C# member names while preserving JSON names", () => {
+        const schema: JSONSchema7 = {
+            definitions: {
+                SessionEvent: {
+                    anyOf: [
+                        {
+                            type: "object",
+                            required: ["type", "data"],
+                            properties: {
+                                type: { const: "session.synthetic" },
+                                data: {
+                                    type: "object",
+                                    required: ["_meta"],
+                                    properties: {
+                                        _meta: { type: "string" },
+                                    },
+                                },
+                            },
+                        },
+                    ],
+                },
+            },
+        };
+
+        const csharpCode = generateCSharpSessionEventsCode(schema);
+
+        expect(csharpCode).toContain(
+            '[JsonPropertyName("_meta")]\n    public required string Meta { get; set; }'
+        );
+        expect(csharpCode).not.toContain("public required string _meta");
+    });
+
     it("collapses redundant callable wrapper lambdas", () => {
         const schema: JSONSchema7 = {
             definitions: {

dotnet/src/Generated/SessionEvents.cs

@@ -3,14 +3,13 @@ use std::path::Path;
 
 use github_copilot_sdk::rpc::{
     ExtensionsDisableRequest, ExtensionsEnableRequest, McpAppsCallToolRequest,
-    McpAppsDiagnoseRequest, McpAppsListToolsRequest, McpAppsReadResourceRequest,
-    McpAppsSetHostContextDetails, McpAppsSetHostContextDetailsAvailableDisplayMode,
-    McpAppsSetHostContextDetailsDisplayMode, McpAppsSetHostContextDetailsPlatform,
-    McpAppsSetHostContextDetailsTheme, McpAppsSetHostContextRequest,
-    McpCancelSamplingExecutionParams, McpDisableRequest, McpEnableRequest,
-    McpExecuteSamplingParams, McpExecuteSamplingRequest, McpOauthLoginRequest,
-    McpSamplingExecutionAction, McpSetEnvValueModeDetails, McpSetEnvValueModeParams,
-    SkillsDisableRequest, SkillsEnableRequest,
+    McpAppsDiagnoseRequest, McpAppsListToolsRequest, McpAppsSetHostContextDetails,
+    McpAppsSetHostContextDetailsAvailableDisplayMode, McpAppsSetHostContextDetailsDisplayMode,
+    McpAppsSetHostContextDetailsPlatform, McpAppsSetHostContextDetailsTheme,
+    McpAppsSetHostContextRequest, McpCancelSamplingExecutionParams, McpDisableRequest,
+    McpEnableRequest, McpExecuteSamplingParams, McpExecuteSamplingRequest, McpOauthLoginRequest,
+    McpResourcesReadRequest, McpSamplingExecutionAction, McpSetEnvValueModeDetails,
+    McpSetEnvValueModeParams, SkillsDisableRequest, SkillsEnableRequest,
 };
 use github_copilot_sdk::{IndexMap, McpServerConfig, McpStdioServerConfig};
 
@@ -510,8 +509,8 @@ async fn should_report_error_when_mcp_app_resource_is_not_available() {
                 let err = session
                     .rpc()
                     .mcp()
-                    .apps()
-                    .read_resource(McpAppsReadResourceRequest {
+                    .resources()
+                    .read(McpResourcesReadRequest {
                         server_name: "missing-app-server".to_string(),
                         uri: "ui://missing/resource.html".to_string(),
                     })

nodejs/test/session-event-codegen.test.ts

@@ -230,7 +230,8 @@ function stripDurationMillisecondsSuffix(name: string): string {
 }
 
 function toCSharpPropertyName(propName: string, schema: JSONSchema7): string {
-    return toPascalCase(isDurationProperty(schema) ? stripDurationMillisecondsSuffix(propName) : propName);
+    const normalizedName = propName.replace(/^_+/, "") || propName;
+    return toPascalCase(isDurationProperty(schema) ? stripDurationMillisecondsSuffix(normalizedName) : normalizedName);
 }
 
 function isSecondsDurationPropertyName(propName: string | undefined): boolean {