[Bugfix] Honor the requested output canvas in BAGEL img2img (#7287)

Signed-off-by: Ding Zuhao <e1583181@u.nus.edu>
Co-authored-by: Cursor <cursoragent@cursor.com>

tests/entrypoints/openai_api/test_image_server.py

@@ -1719,7 +1719,7 @@ def test_image_edit_parameter_pass(async_omni_test_client):
         img = Image.open(io.BytesIO(img_bytes))
         assert img.format.lower() == "jpeg"
         assert data["output_format"] == "jpeg"
-        assert data["size"] == "16x24"
+        assert data["size"] == "64x64"
 
 
 def test_image_edit_layers_and_resolution(async_omni_test_client):
@@ -1896,6 +1896,7 @@ def test_image_edit_parameter_default_single_stage(test_client):
 
     assert captured_sampling_params.width == 24
     assert captured_sampling_params.height == 16
+    assert (captured_sampling_params.height_not_provided, captured_sampling_params.width_not_provided) == (True, True)
     assert captured_sampling_params.num_outputs_per_prompt == 1
     assert captured_sampling_params.num_inference_steps == 4
     assert captured_sampling_params.guidance_scale == 7.5
@@ -1913,6 +1914,40 @@ def test_image_edit_parameter_default_single_stage(test_client):
     assert response.status_code == 400
 
 
+def test_image_edit_explicit_size_marks_canvas_provided_single_stage(test_client):
+    response = test_client.post(
+        "/v1/images/edits",
+        files=[("image", make_test_image_bytes((24, 16)))],
+        data={"prompt": "hello world.", "size": "16x24"},
+    )
+
+    assert response.status_code == 200
+    sampling = test_client.app.state.engine_client.captured_sampling_params_list[0]
+    assert (sampling.height, sampling.width) == (24, 16)
+    assert (sampling.height_not_provided, sampling.width_not_provided) == (False, False)
+
+
+def test_image_edit_response_size_reports_generated_image_single_stage(test_client):
+    response = test_client.post(
+        "/v1/images/edits",
+        files=[("image", make_test_image_bytes((24, 16)))],
+        data={"prompt": "hello world.", "size": "16x24"},
+    )
+
+    assert response.status_code == 200
+    assert response.json()["size"] == "64x64"
+
+
+def test_generate_images_response_size_reports_generated_image(test_client):
+    response = test_client.post(
+        "/v1/images/generations",
+        json={"prompt": "a cat", "n": 1, "size": "1024x1024"},
+    )
+
+    assert response.status_code == 200
+    assert response.json()["size"] == "64x64"
+
+
 def test_image_edit_compression_jpeg(test_client):
     img_bytes_1 = make_test_image_bytes((16, 16))
     # uploadfile with image key