feat: capture MCP client info in User-Agent

When an MCP client (like Claude Desktop or Cursor) connects, we now
capture its name and version from the initialize request and include
it in the User-Agent string.

Format: context-connectors/{version} via:mcp client:{name}/{version}
Example: context-connectors/0.1.3 via:mcp client:claude-desktop/1.0.0

Changes:
- Add updateClientUserAgent() method to MultiIndexRunner
- Handle InitializeRequestSchema in mcp-server.ts to capture client info
- Update User-Agent dynamically after receiving MCP client info

Agent-Id: agent-0d00d75b-1ac5-4e85-a310-90e1af295ee3

Author: richhankins

src/clients/mcp-server.ts

@@ -36,10 +36,11 @@ import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js"
 import {
   CallToolRequestSchema,
   ListToolsRequestSchema,
+  InitializeRequestSchema,
 } from "@modelcontextprotocol/sdk/types.js";
 import type { IndexStoreReader } from "../stores/types.js";
 import { MultiIndexRunner } from "./multi-index-runner.js";
-import { buildClientUserAgent } from "../core/utils.js";
+import { buildClientUserAgent, type MCPClientInfo } from "../core/utils.js";
 import {
   SEARCH_DESCRIPTION,
   LIST_FILES_DESCRIPTION,
@@ -126,6 +127,35 @@ export async function createMCPServer(
     }
   );
 
+  // Set up a custom initialize handler to capture MCP client info
+  // We intercept the initialize request to update the User-Agent with client info
+  server.setRequestHandler(InitializeRequestSchema, async (request) => {
+    // Extract client info from the initialize request
+    const clientInfo = request.params.clientInfo;
+    if (clientInfo) {
+      const mcpClientInfo: MCPClientInfo = {
+        name: clientInfo.name,
+        version: clientInfo.version,
+      };
+      // Update the runner's User-Agent with MCP client info
+      const updatedUserAgent = buildClientUserAgent("mcp", mcpClientInfo);
+      runner.updateClientUserAgent(updatedUserAgent);
+    }
+
+    // Return the standard initialize response
+    // The Server class will merge our capabilities with the standard response
+    return {
+      protocolVersion: "2024-11-05",
+      serverInfo: {
+        name: config.serverName ?? "context-connectors",
+        version: config.version ?? "0.1.0",
+      },
+      capabilities: {
+        tools: {},
+      },
+    };
+  });
+
   // Define tool type for type safety
   type Tool = {
     name: string;

src/clients/multi-index-runner.ts

@@ -70,7 +70,7 @@ async function createSourceFromState(state: IndexStateSearchOnly): Promise<Sourc
 export class MultiIndexRunner {
   private readonly store: IndexStoreReader;
   private readonly searchOnly: boolean;
-  private readonly clientUserAgent?: string;
+  private clientUserAgent?: string;
   private readonly clientCache = new Map<string, SearchClient>();
 
   /** Available index names */
@@ -143,6 +143,17 @@ export class MultiIndexRunner {
     return new MultiIndexRunner(store, validIndexNames, indexes, searchOnly, config.clientUserAgent);
   }
 
+
+  /**
+   * Update the User-Agent string.
+   * 
+   * Call this after receiving MCP client info to include the client name/version.
+   * Note: Only affects future client creations, not existing cached clients.
+   */
+  updateClientUserAgent(newUserAgent: string): void {
+    this.clientUserAgent = newUserAgent;
+  }
+
   /**
    * Get or create a SearchClient for an index.
    */