Improve Function Call argument validation and typing (#2881)

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

packages/core/src/tools/read-file.ts

@@ -8,6 +8,7 @@ import path from 'path';
 import { SchemaValidator } from '../utils/schemaValidator.js';
 import { makeRelative, shortenPath } from '../utils/paths.js';
 import { BaseTool, ToolResult } from './tools.js';
+import { Type } from '@google/genai';
 import {
   isWithinRoot,
   processSingleFileContent,
@@ -58,37 +59,33 @@ export class ReadFileTool extends BaseTool<ReadFileToolParams, ToolResult> {
           absolute_path: {
             description:
               "The absolute path to the file to read (e.g., '/home/user/project/file.txt'). Relative paths are not supported. You must provide an absolute path.",
-            type: 'string',
+            type: Type.STRING,
             pattern: '^/',
           },
           offset: {
             description:
               "Optional: For text files, the 0-based line number to start reading from. Requires 'limit' to be set. Use for paginating through large files.",
-            type: 'number',
+            type: Type.NUMBER,
           },
           limit: {
             description:
               "Optional: For text files, maximum number of lines to read. Use with 'offset' to paginate through large files. If omitted, reads the entire file (if feasible, up to a default limit).",
-            type: 'number',
+            type: Type.NUMBER,
           },
         },
         required: ['absolute_path'],
-        type: 'object',
+        type: Type.OBJECT,
       },
     );
     this.rootDirectory = path.resolve(rootDirectory);
   }
 
   validateToolParams(params: ReadFileToolParams): 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;
     }
+
     const filePath = params.absolute_path;
     if (!path.isAbsolute(filePath)) {
       return `File path must be absolute, but was relative: ${filePath}. You must provide an absolute path.`;