feat: support protocol version 2025-11-25 (#81)

- Update client initialization check to accept both 2025-06-18 and 2025-11-25
- Server echoes back client's version if valid (proper version negotiation)
- Fixes compatibility with SDK 1.25.1+ which sends 2025-11-25

🦉 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

src/checks/client.ts

@@ -23,12 +23,20 @@ export function createServerInfoCheck(serverInfo: {
   };
 }
 
+// Valid MCP protocol versions
+const VALID_PROTOCOL_VERSIONS = ['2025-06-18', '2025-11-25'];
+
 export function createClientInitializationCheck(
   initializeRequest: any,
-  expectedSpecVersion: string = '2025-06-18'
+  expectedSpecVersion: string = '2025-11-25'
 ): ConformanceCheck {
   const protocolVersionSent = initializeRequest?.protocolVersion;
-  const versionMatch = protocolVersionSent === expectedSpecVersion;
+
+  // Accept known valid versions OR custom expected version (for backward compatibility)
+  const validVersions = VALID_PROTOCOL_VERSIONS.includes(expectedSpecVersion)
+    ? VALID_PROTOCOL_VERSIONS
+    : [...VALID_PROTOCOL_VERSIONS, expectedSpecVersion];
+  const versionMatch = validVersions.includes(protocolVersionSent);
 
   const errors: string[] = [];
   if (!protocolVersionSent) errors.push('Protocol version not provided');

src/scenarios/client/initialize.ts

@@ -110,11 +110,18 @@ export class InitializeScenario implements Scenario {
 
     this.checks.push(clientChecks.createServerInfoCheck(serverInfo));
 
+    // Echo back client's version if valid, otherwise use latest
+    const VALID_VERSIONS = ['2025-06-18', '2025-11-25'];
+    const clientVersion = initializeRequest?.protocolVersion;
+    const responseVersion = VALID_VERSIONS.includes(clientVersion)
+      ? clientVersion
+      : '2025-11-25';
+
     const response = {
       jsonrpc: '2.0',
       id: request.id,
       result: {
-        protocolVersion: '2025-06-18',
+        protocolVersion: responseVersion,
         serverInfo,
         capabilities: {}
       }