fix: add .passthrough() to ToolSchema.outputSchema

Preserve JSON Schema properties like additionalProperties when parsing
tool output schemas. This allows proper validation of structured content
that uses additionalProperties: false.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: ochafik

scripts/generate-schemas.ts

@@ -99,6 +99,14 @@ const ARRAY_DEFAULT_FIELDS: Record<string, string[]> = {
     'ToolResultContentSchema': ['content'],
 };
 
+/**
+ * Fields that need .passthrough() to preserve unknown JSON Schema properties.
+ * These are JSON Schema objects where extra properties like additionalProperties must be kept.
+ */
+const PASSTHROUGH_FIELDS: Record<string, string[]> = {
+    'ToolSchema': ['outputSchema'],
+};
+
 /**
  * Schemas that need .strict() added for stricter validation.
  */
@@ -658,6 +666,7 @@ const AST_TRANSFORMS: Transform[] = [
     transformTypeofExpressions,
     transformIntegerRefinements,
     transformArrayDefaults,
+    transformPassthroughFields,
     transformUnionToEnum,
     applyFieldOverrides,
     addStrictToSchemas,
@@ -685,6 +694,17 @@ function postProcess(content: string): string {
 // Run: npm run generate:schemas`,
     );
 
+    // Add .passthrough() to outputSchema to preserve JSON Schema properties like additionalProperties
+    // Pattern matches: outputSchema: z.object({...}).optional()
+    // We need to insert .passthrough() before .optional()
+    // Note: ts-to-zod generates inline, so pattern is: outputSchema: z.object({...}).optional()
+    const outputSchemaPattern = /(outputSchema:\s*z\.object\(\{[\s\S]*?\}\))(\.optional\(\))/g;
+    const newContent = content.replace(outputSchemaPattern, '$1.passthrough()$2');
+    if (newContent !== content) {
+        content = newContent;
+        console.log('    ✓ Added .passthrough() to ToolSchema.outputSchema');
+    }
+
     // AST-based transforms using ts-morph
     const project = new Project({ useInMemoryFileSystem: true });
     const sourceFile = project.createSourceFile('schemas.ts', content);
@@ -815,6 +835,14 @@ function transformArrayDefaults(sourceFile: SourceFile): void {
     }
 }
 
+/**
+ * Add .passthrough() to fields that need to preserve unknown JSON Schema properties.
+ * This is done via text replacement in postProcess since the structure is complex.
+ */
+function transformPassthroughFields(_sourceFile: SourceFile): void {
+    // This is handled in postProcess via text replacement for simplicity
+}
+
 /**
  * Transform z.union([z.literal('a'), z.literal('b'), ...]) to z.enum(['a', 'b', ...])
  *

src/generated/sdk.schemas.ts

@@ -1041,6 +1041,7 @@ export const ToolSchema = BaseMetadataSchema.extend(IconsSchema.shape)
                 properties: z.record(z.string(), z.record(z.string(), z.any())).optional(),
                 required: z.array(z.string()).optional()
             })
+            .passthrough()
             .optional()
             .describe(
                 'An optional JSON Schema object defining the structure of the tool\'s output returned in\nthe structuredContent field of a CallToolResult.\n\nDefaults to JSON Schema 2020-12 when no explicit $schema is provided.\nCurrently restricted to type: "object" at the root level.'