fix(core): align JSON Schema required fields with Zod (#549)

packages/core/src/tool/framework.ts

@@ -370,12 +370,7 @@ function convertZodType(schema: ZodSchema): Record<string, unknown> {
       for (const [key, value] of Object.entries(objectDef.shape())) {
         properties[key] = convertZodType(value as ZodSchema)
 
-        const innerDef = ((value as ZodSchema) as unknown as { _def: ZodTypeDef })._def
-        const isOptional =
-          innerDef.typeName === ZodTypeName.ZodOptional ||
-          innerDef.typeName === ZodTypeName.ZodDefault ||
-          innerDef.typeName === ZodTypeName.ZodNullable
-        if (!isOptional) {
+        if (!(value as ZodSchema).isOptional()) {
           required.push(key)
         }
       }

packages/core/tests/tool-executor.test.ts

@@ -317,6 +317,26 @@ describe('ToolRegistry', () => {
     expect(defs[0].name).toBe('echo')
     expect(defs[0].inputSchema).toHaveProperty('properties')
   })
+
+  it('marks nullable inputs as required when Zod rejects omission', () => {
+    const inputSchema = z.object({
+      requiredNullable: z.string().nullable(),
+      optional: z.string().optional(),
+    })
+    const registry = new ToolRegistry()
+    registry.register(defineTool({
+      name: 'nullable_input',
+      description: 'Accepts a required nullable value.',
+      inputSchema,
+      execute: async () => ({ data: 'ok' }),
+    }))
+
+    const [definition] = registry.toToolDefs()
+
+    expect(inputSchema.safeParse({}).success).toBe(false)
+    expect(inputSchema.safeParse({ requiredNullable: null }).success).toBe(true)
+    expect(definition.inputSchema).toMatchObject({ required: ['requiredNullable'] })
+  })
 })
 
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