feat(congodb): implement CongoDB MongoDB wire-protocol compatible in-memory server and APIs

ts/congodb/server/handlers/HelloHandler.ts

@@ -0,0 +1,78 @@
+import * as plugins from '../../congodb.plugins.js';
+import type { ICommandHandler, IHandlerContext } from '../CommandRouter.js';
+
+/**
+ * HelloHandler - Handles hello/isMaster handshake commands
+ *
+ * This is the first command sent by MongoDB drivers to establish a connection.
+ * It returns server capabilities and configuration.
+ */
+export class HelloHandler implements ICommandHandler {
+  async handle(context: IHandlerContext): Promise<plugins.bson.Document> {
+    const { command, server } = context;
+
+    // Build response with server capabilities
+    const response: plugins.bson.Document = {
+      ismaster: true,
+      ok: 1,
+
+      // Maximum sizes
+      maxBsonObjectSize: 16777216,           // 16 MB
+      maxMessageSizeBytes: 48000000,         // 48 MB
+      maxWriteBatchSize: 100000,             // 100k documents per batch
+
+      // Timestamps
+      localTime: new Date(),
+
+      // Session support
+      logicalSessionTimeoutMinutes: 30,
+
+      // Connection info
+      connectionId: 1,
+
+      // Wire protocol versions (support MongoDB 3.6 through 7.0)
+      minWireVersion: 0,
+      maxWireVersion: 21,
+
+      // Server mode
+      readOnly: false,
+
+      // Topology info (standalone mode)
+      isWritablePrimary: true,
+
+      // Additional info
+      topologyVersion: {
+        processId: new plugins.bson.ObjectId(),
+        counter: plugins.bson.Long.fromNumber(0),
+      },
+    };
+
+    // Handle hello-specific fields
+    if (command.hello || command.hello === 1) {
+      response.helloOk = true;
+    }
+
+    // Handle client metadata
+    if (command.client) {
+      // Client is providing metadata about itself
+      // We just acknowledge it - no need to do anything special
+    }
+
+    // Handle SASL mechanisms query
+    if (command.saslSupportedMechs) {
+      response.saslSupportedMechs = [
+        // We don't actually support auth, but the driver needs to see this
+      ];
+    }
+
+    // Compression support (none for now)
+    if (command.compression) {
+      response.compression = [];
+    }
+
+    // Server version info
+    response.version = '7.0.0';
+
+    return response;
+  }
+}