Improve Function Call argument validation and typing (#2881)

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

packages/core/src/tools/edit.ts

@@ -15,6 +15,7 @@ import {
   ToolResult,
   ToolResultDisplay,
 } from './tools.js';
+import { Type } from '@google/genai';
 import { SchemaValidator } from '../utils/schemaValidator.js';
 import { makeRelative, shortenPath } from '../utils/paths.js';
 import { isNodeError } from '../utils/errors.js';
@@ -97,27 +98,27 @@ Expectation for required parameters:
           file_path: {
             description:
               "The absolute path to the file to modify. Must start with '/'.",
-            type: 'string',
+            type: Type.STRING,
           },
           old_string: {
             description:
               'The exact literal text to replace, preferably unescaped. For single replacements (default), include at least 3 lines of context BEFORE and AFTER the target text, matching whitespace and indentation precisely. For multiple replacements, specify expected_replacements parameter. If this string is not the exact literal text (i.e. you escaped it) or does not match exactly, the tool will fail.',
-            type: 'string',
+            type: Type.STRING,
           },
           new_string: {
             description:
               'The exact literal text to replace `old_string` with, preferably unescaped. Provide the EXACT text. Ensure the resulting code is correct and idiomatic.',
-            type: 'string',
+            type: Type.STRING,
           },
           expected_replacements: {
-            type: 'number',
+            type: Type.NUMBER,
             description:
               'Number of replacements expected. Defaults to 1 if not specified. Use when you want to replace multiple occurrences.',
             minimum: 1,
           },
         },
         required: ['file_path', 'old_string', 'new_string'],
-        type: 'object',
+        type: Type.OBJECT,
       },
     );
     this.rootDirectory = path.resolve(this.config.getTargetDir());
@@ -146,14 +147,9 @@ Expectation for required parameters:
    * @returns Error message string or null if valid
    */
   validateToolParams(params: EditToolParams): 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.file_path)) {