Improve Function Call argument validation and typing (#2881)

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

packages/core/src/tools/grep.ts

@@ -11,6 +11,7 @@ import { EOL } from 'os';
 import { spawn } from 'child_process';
 import { globStream } from 'glob';
 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 { getErrorMessage, isNodeError } from '../utils/errors.js';
@@ -69,21 +70,21 @@ export class GrepTool extends BaseTool<GrepToolParams, ToolResult> {
           pattern: {
             description:
               "The regular expression (regex) pattern to search for within file contents (e.g., 'function\\s+myFunction', 'import\\s+\\{.*\\}\\s+from\\s+.*').",
-            type: 'string',
+            type: Type.STRING,
           },
           path: {
             description:
               'Optional: The absolute path to the directory to search within. If omitted, searches the current working directory.',
-            type: 'string',
+            type: Type.STRING,
           },
           include: {
             description:
               "Optional: A glob pattern to filter which files are searched (e.g., '*.js', '*.{ts,tsx}', 'src/**'). If omitted, searches all files (respecting potential global ignores).",
-            type: 'string',
+            type: Type.STRING,
           },
         },
         required: ['pattern'],
-        type: 'object',
+        type: Type.OBJECT,
       },
     );
     // Ensure rootDirectory is absolute and normalized
@@ -135,14 +136,9 @@ export class GrepTool extends BaseTool<GrepToolParams, ToolResult> {
    * @returns An error message string if invalid, null otherwise
    */
   validateToolParams(params: GrepToolParams): 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;
     }
 
     try {