diff --git a/app/config/openapi.js b/app/config/openapi.js
index 870406a..f0e3151 100644
--- a/app/config/openapi.js
+++ b/app/config/openapi.js
@@ -694,7 +694,21 @@ const spec = {
                         // Declare it so SDK generators surface the field
                         // on the client side.
                         headers: idempotencyReplayResponseHeader,
-                        content: { 'application/json': { schema: { $ref: '#/components/schemas/Customer' } } },
+                        // Controller wraps the row in {message, customer} —
+                        // same envelope pattern fixed for GET in #312.
+                        // Surface the envelope here so SDK code-gen
+                        // doesn't model the body as a bare Customer.
+                        content: {
+                            'application/json': {
+                                schema: {
+                                    type: 'object',
+                                    properties: {
+                                        message: { type: 'string' },
+                                        customer: { $ref: '#/components/schemas/Customer' },
+                                    },
+                                },
+                            },
+                        },
                     },
                     400: { description: 'Bad request' },
                     403: { description: 'Missing or invalid authKey' },
diff --git a/tests/api/openapi.test.js b/tests/api/openapi.test.js
index 0ba3053..2d2f90f 100644
--- a/tests/api/openapi.test.js
+++ b/tests/api/openapi.test.js
@@ -70,6 +70,20 @@ describe('OpenAPI spec', () => {
         expect(schemas.TimeEntry.properties.teStartedAt).toBeDefined();
     });
 
+    test('POST /v1/customer 201 declares the {message, customer} envelope', async () => {
+        // Same envelope-drift fix as the GET endpoint below (#312)
+        // but for the create path. The controller responds with
+        // `{message, customer}` on a successful 201; the spec
+        // previously said the body was a bare Customer, so SDK
+        // generators built clients that failed to find the row.
+        const res = await request(app).get('/openapi.json');
+        const r201 = res.body.paths['/v1/customer'].post.responses['201'];
+        const schema = r201.content['application/json'].schema;
+        expect(schema.type).toBe('object');
+        expect(schema.properties.message).toBeDefined();
+        expect(schema.properties.customer.$ref).toBe('#/components/schemas/Customer');
+    });
+
     test('GET /v1/customer/{id} 200 declares the {message, customer, customers} envelope', async () => {
         // Pre-#292 the spec said the body was a bare Customer. The
         // controller actually returns a `{message, customer, customers}`