Improve Function Call argument validation and typing (#2881)

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

packages/core/src/tools/shell.ts

@@ -16,6 +16,7 @@ import {
   ToolExecuteConfirmationDetails,
   ToolConfirmationOutcome,
 } from './tools.js';
+import { Type } from '@google/genai';
 import { SchemaValidator } from '../utils/schemaValidator.js';
 import { getErrorMessage } from '../utils/errors.js';
 import stripAnsi from 'strip-ansi';
@@ -51,19 +52,19 @@ Signal: Signal number or \`(none)\` if no signal was received.
 Background PIDs: List of background processes started or \`(none)\`.
 Process Group PGID: Process group started or \`(none)\``,
       {
-        type: 'object',
+        type: Type.OBJECT,
         properties: {
           command: {
-            type: 'string',
+            type: Type.STRING,
             description: 'Exact bash command to execute as `bash -c <command>`',
           },
           description: {
-            type: 'string',
+            type: Type.STRING,
             description:
               'Brief description of the command for the user. Be specific and concise. Ideally a single sentence. Can be up to 3 sentences for clarity. No line breaks.',
           },
           directory: {
-            type: 'string',
+            type: Type.STRING,
             description:
               '(OPTIONAL) Directory to run the command in, if not the project root directory. Must be relative to the project root directory and must already exist.',
           },
@@ -223,13 +224,9 @@ Process Group PGID: Process group started or \`(none)\``,
       }
       return commandCheck.reason;
     }
-    if (
-      !SchemaValidator.validate(
-        this.parameterSchema as Record<string, unknown>,
-        params,
-      )
-    ) {
-      return `Parameters failed schema validation.`;
+    const errors = SchemaValidator.validate(this.schema.parameters, params);
+    if (errors) {
+      return errors;
     }
     if (!params.command.trim()) {
       return 'Command cannot be empty.';