fix more tests

Author: nirinchev

src/tools/mongodb/metadata/explain.ts

@@ -16,7 +16,7 @@ export class ExplainTool extends MongoDBToolBase {
         ...DbOperationArgs,
         method: z
             .array(
-                z.union([
+                z.discriminatedUnion("name", [
                     z.object({
                         name: z.literal("aggregate"),
                         arguments: z.object(AggregateArgs),

src/tools/mongodb/read/aggregate.ts

@@ -6,7 +6,7 @@ import { EJSON } from "bson";
 import { checkIndexUsage } from "../../../helpers/indexCheck.js";
 
 export const AggregateArgs = {
-    pipeline: z.array(z.record(z.string(), z.unknown())).describe("An array of aggregation stages to execute"),
+    pipeline: z.array(z.object({}).passthrough()).describe("An array of aggregation stages to execute"),
 };
 
 export class AggregateTool extends MongoDBToolBase {