fix: add .default([]) to content arrays and fix test capabilities

- Add transformArrayDefaults to schema generation for backwards compatibility
- CallToolResultSchema.content and ToolResultContentSchema.content now default to []
- Fix mcp.test.ts server capabilities to use correct tasks.requests.tools.call structure

This fixes test failures caused by stricter schema validation requiring content arrays.

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

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

Author: ochafik

scripts/generate-schemas.ts

@@ -17,6 +17,7 @@
  *    - `z.record().and(z.object())` → `z.looseObject()`
  *    - `jsonrpc: z.any()` → `z.literal("2.0")`
  *    - Add `.int()` refinements to ProgressTokenSchema, RequestIdSchema
+ *    - Add `.default([])` to content arrays for backwards compatibility
  *    - `z.union([z.literal("a"), ...])` → `z.enum(["a", ...])`
  *    - Field-level validation overrides (datetime, startsWith, etc.)
  *
@@ -89,6 +90,15 @@ const FIELD_OVERRIDES: Record<string, Record<string, string>> = {
  */
 const INTEGER_SCHEMAS = ['ProgressTokenSchema', 'RequestIdSchema'];
 
+/**
+ * Fields that need .default([]) for backwards compatibility.
+ * The SDK historically made these optional with empty array defaults.
+ */
+const ARRAY_DEFAULT_FIELDS: Record<string, string[]> = {
+    'CallToolResultSchema': ['content'],
+    'ToolResultContentSchema': ['content'],
+};
+
 /**
  * Schemas that need .strict() added for stricter validation.
  */
@@ -616,6 +626,7 @@ const AST_TRANSFORMS: Transform[] = [
     transformRecordAndToLooseObject,
     transformTypeofExpressions,
     transformIntegerRefinements,
+    transformArrayDefaults,
     transformUnionToEnum,
     applyFieldOverrides,
     addStrictToSchemas,
@@ -740,6 +751,39 @@ function transformIntegerRefinements(sourceFile: SourceFile): void {
     }
 }
 
+/**
+ * Add .default([]) to array fields for backwards compatibility.
+ * The SDK historically made certain content arrays optional with empty defaults.
+ */
+function transformArrayDefaults(sourceFile: SourceFile): void {
+    for (const [schemaName, fieldNames] of Object.entries(ARRAY_DEFAULT_FIELDS)) {
+        const varDecl = sourceFile.getVariableDeclaration(schemaName);
+        if (!varDecl) continue;
+
+        const initializer = varDecl.getInitializer();
+        if (!initializer) continue;
+
+        // Find property assignments for the target fields
+        initializer.forEachDescendant((node) => {
+            if (!Node.isPropertyAssignment(node)) return;
+
+            const propName = node.getName();
+            if (!fieldNames.includes(propName)) return;
+
+            // Get the initializer (the value assigned to the property)
+            const propInit = node.getInitializer();
+            if (!propInit) return;
+
+            const propText = propInit.getText();
+            // Only add .default([]) if it's a z.array() and doesn't already have .default()
+            if (propText.includes('z.array(') && !propText.includes('.default(')) {
+                // Append .default([]) to the existing expression
+                propInit.replaceWithText(propText + '.default([])');
+            }
+        });
+    }
+}
+
 /**
  * Transform z.union([z.literal('a'), z.literal('b'), ...]) to z.enum(['a', 'b', ...])
  *

src/generated/sdk.schemas.ts

@@ -2259,7 +2259,8 @@ export const ToolResultContentSchema = z
             .array(ContentBlockSchema)
             .describe(
                 'The unstructured result content of the tool use.\n\nThis has the same format as CallToolResult.content and can include text, images,\naudio, resource links, and embedded resources.'
-            ),
+            )
+            .default([]),
         /** @description An optional structured result object.
           
               If the tool defined an outputSchema, this SHOULD conform to that schema. */
@@ -2389,7 +2390,10 @@ export const ListResourcesResultSchema = PaginatedResultSchema.extend({
  */
 export const CallToolResultSchema = ResultSchema.extend({
     /** @description A list of content objects that represent the unstructured result of the tool call. */
-    content: z.array(ContentBlockSchema).describe('A list of content objects that represent the unstructured result of the tool call.'),
+    content: z
+        .array(ContentBlockSchema)
+        .describe('A list of content objects that represent the unstructured result of the tool call.')
+        .default([]),
     /** @description An optional JSON object that represents the structured result of the tool call. */
     structuredContent: z
         .record(z.string(), z.unknown())

test/server/mcp.test.ts

@@ -6456,8 +6456,11 @@ describe.each(zodTestMatrix)('$zodVersionLabel', (entry: ZodMatrixEntry) => {
                     capabilities: {
                         tools: {},
                         tasks: {
-                            list: {},
-                            cancel: {}
+                            requests: {
+                                tools: {
+                                    call: {}
+                                }
+                            }
                         }
                     },
                     taskStore