feat: add MVP stateless client conformance tests for SEP-2575

Author: anubhav756

src/scenarios/client/stateless.ts

@@ -0,0 +1,101 @@
+import http from 'http';
+import {
+  Scenario,
+  ScenarioUrls,
+  ConformanceCheck,
+  SpecVersion,
+  DRAFT_PROTOCOL_VERSION
+} from '../../types';
+
+export class StatelessClientScenario implements Scenario {
+  name = 'stateless-client';
+  specVersions: SpecVersion[] = ['2026-06-18', DRAFT_PROTOCOL_VERSION];
+  description = 'Tests stateless MCP client behavior (SEP-2575)';
+
+  private server: http.Server | null = null;
+  private checks: ConformanceCheck[] = [];
+
+  async start(): Promise<ScenarioUrls> {
+    return new Promise((resolve, reject) => {
+      this.server = http.createServer((req, res) => {
+        this.handleRequest(req, res);
+      });
+      this.server.on('error', reject);
+      this.server.listen(0, () => {
+        const address = this.server!.address();
+        if (address && typeof address === 'object') {
+          resolve({ serverUrl: `http://localhost:${address.port}` });
+        }
+      });
+    });
+  }
+
+  async stop(): Promise<void> {
+    return new Promise((resolve) => {
+      if (this.server) {
+        this.server.close(() => { resolve(); });
+      } else {
+        resolve();
+      }
+    });
+  }
+
+  getChecks(): ConformanceCheck[] {
+    return this.checks;
+  }
+
+  private handleRequest(req: http.IncomingMessage, res: http.ServerResponse): void {
+    let body = '';
+    req.on('data', (chunk) => { body += chunk.toString(); });
+    req.on('end', () => {
+      const request = JSON.parse(body);
+
+      // TEST 1: Verify client can call server/discover
+      if (request.method === 'server/discover') {
+        this.checks.push({
+          id: 'client-calls-discover',
+          name: 'ClientCallsDiscover',
+          description: 'Client is able to successfully call server/discover',
+          status: 'SUCCESS',
+          timestamp: new Date().toISOString(),
+          specReferences: [{ id: 'SEP-2575', url: '' }]
+        });
+        
+        // Respond with valid discovery payload to keep client happy
+        res.writeHead(200, { 'Content-Type': 'application/json' });
+        res.end(JSON.stringify({
+          jsonrpc: '2.0',
+          id: request.id,
+          result: { 
+            supportedVersions: ['2026-06-18'], 
+            capabilities: {}, 
+            serverInfo: { name: 'test', version: '1.0' } 
+          }
+        }));
+        return;
+      }
+
+      // TEST 2: Verify inline _meta on every request
+      const meta = request.params?._meta;
+      const hasProtocolVersion = meta?.['io.modelcontextprotocol/protocolVersion'];
+      const hasClientInfo = meta?.['io.modelcontextprotocol/clientInfo'];
+      const hasCapabilities = meta?.['io.modelcontextprotocol/clientCapabilities'];
+
+      const metaIsValid = hasProtocolVersion && hasClientInfo && hasCapabilities;
+
+      this.checks.push({
+        id: 'client-populates-meta',
+        name: 'ClientPopulatesMeta',
+        description: 'Client populates _meta on every request with all three required fields',
+        status: metaIsValid ? 'SUCCESS' : 'FAILURE',
+        timestamp: new Date().toISOString(),
+        specReferences: [{ id: 'SEP-2575', url: '' }],
+        details: { meta }
+      });
+
+      // Return generic response to unblock client
+      res.writeHead(200, { 'Content-Type': 'application/json' });
+      res.end(JSON.stringify({ jsonrpc: '2.0', id: request.id, result: {} }));
+    });
+  }
+}

src/scenarios/index.ts

@@ -12,6 +12,7 @@ import { InitializeScenario } from './client/initialize';
 import { ToolsCallScenario } from './client/tools_call';
 import { ElicitationClientDefaultsScenario } from './client/elicitation-defaults';
 import { SSERetryScenario } from './client/sse-retry';
+import { StatelessClientScenario } from './client/stateless';
 
 // Import all new server test scenarios
 import { ServerInitializeScenario } from './server/lifecycle';
@@ -182,6 +183,7 @@ const scenariosList: Scenario[] = [
   ...authScenariosList,
   ...backcompatScenariosList,
   ...draftScenariosList,
+  new StatelessClientScenario(),
   ...extensionScenariosList
 ];