feat(customer): add CustomerLookupToolSchema for MCP tools

xmcp requires .shape property for tool schema generation, which only
ZodObject has. ZodUnion (CustomerLookupInputSchema) lacks .shape.

Add CustomerLookupToolSchema as a flat object with all optional fields
for MCP tools, while keeping the discriminated union for contract
validation.

Author: martinsaposnic

src/contracts/customer.ts

@@ -31,7 +31,7 @@ export type ListCustomersPaginatedOutput = z.infer<
 	typeof ListCustomersPaginatedOutputSchema
 >;
 
-// Customer lookup by exactly one identifier (discriminated union for JSON Schema compatibility)
+// Customer lookup by exactly one identifier (discriminated union for contract validation)
 const CustomerLookupByIdSchema = z.object({
 	id: z.string().describe("The customer ID"),
 });
@@ -49,6 +49,13 @@ export const CustomerLookupInputSchema = z.union([
 ]);
 export type CustomerLookupInput = z.infer<typeof CustomerLookupInputSchema>;
 
+// Flat schema for MCP tools (xmcp needs .shape, unions don't have it)
+export const CustomerLookupToolSchema = z.object({
+	id: z.string().optional().describe("The customer ID"),
+	email: z.string().optional().describe("The customer email address"),
+	externalId: z.string().optional().describe("The external ID from your system"),
+});
+
 export const GetCustomerInputSchema = CustomerLookupInputSchema;
 export type GetCustomerInput = z.infer<typeof GetCustomerInputSchema>;
 

src/index.ts

@@ -65,6 +65,7 @@ export {
 	GetCustomerInputSchema,
 	DeleteCustomerInputSchema,
 	CustomerLookupInputSchema,
+	CustomerLookupToolSchema,
 } from "./contracts/customer";
 export type { Checkout } from "./schemas/checkout";
 export { CheckoutSchema } from "./schemas/checkout";