test(agentfield): add regression test for issue #587

Ref: #587
Signed-off-by: Jay <sallomondiei@gmail.com>

Author: Jay

tests/test_issue_587.py

@@ -0,0 +1,18 @@
+"""Regression test for issue #587 -- ImageOutput.save() with data URLs."""
+
+import base64
+
+from agentfield.multimodal_response import ImageOutput
+
+
+def test_issue_587(tmp_path):
+    """Gemini-style data URLs should save locally without an HTTP request."""
+    image_bytes = b"\x89PNG\r\n\x1a\nissue-587"
+    image = ImageOutput(
+        url=f"data:image/png;base64,{base64.b64encode(image_bytes).decode()}"
+    )
+    output_path = tmp_path / "gemini-image.png"
+
+    image.save(output_path)
+
+    assert output_path.read_bytes() == image_bytes