Improve Function Call argument validation and typing (#2881)

Co-authored-by: N. Taylor Mullen <ntaylormullen@google.com>

packages/core/src/tools/ls.ts

@@ -7,6 +7,7 @@
 import fs from 'fs';
 import path from 'path';
 import { BaseTool, ToolResult } from './tools.js';
+import { Type } from '@google/genai';
 import { SchemaValidator } from '../utils/schemaValidator.js';
 import { makeRelative, shortenPath } from '../utils/paths.js';
 import { Config } from '../config/config.js';
@@ -84,23 +85,23 @@ export class LSTool extends BaseTool<LSToolParams, ToolResult> {
           path: {
             description:
               'The absolute path to the directory to list (must be absolute, not relative)',
-            type: 'string',
+            type: Type.STRING,
           },
           ignore: {
             description: 'List of glob patterns to ignore',
             items: {
-              type: 'string',
+              type: Type.STRING,
             },
-            type: 'array',
+            type: Type.ARRAY,
           },
           respect_git_ignore: {
             description:
               'Optional: Whether to respect .gitignore patterns when listing files. Only available in git repositories. Defaults to true.',
-            type: 'boolean',
+            type: Type.BOOLEAN,
           },
         },
         required: ['path'],
-        type: 'object',
+        type: Type.OBJECT,
       },
     );
 
@@ -132,14 +133,9 @@ export class LSTool extends BaseTool<LSToolParams, ToolResult> {
    * @returns An error message string if invalid, null otherwise
    */
   validateToolParams(params: LSToolParams): string | null {
-    if (
-      this.schema.parameters &&
-      !SchemaValidator.validate(
-        this.schema.parameters as Record<string, unknown>,
-        params,
-      )
-    ) {
-      return 'Parameters failed schema validation.';
+    const errors = SchemaValidator.validate(this.schema.parameters, params);
+    if (errors) {
+      return errors;
     }
     if (!path.isAbsolute(params.path)) {
       return `Path must be absolute: ${params.path}`;