fix: catch UnicodeDecodeError in _handle_error_response

src/celeste/client.py

@@ -324,7 +324,13 @@ def _handle_error_response(self, response: httpx.Response) -> None:
         if not response.is_success:
             try:
                 error_msg = response.json()["error"]["message"]
-            except (JSONDecodeError, KeyError, TypeError, IndexError):
+            except (
+                JSONDecodeError,
+                KeyError,
+                TypeError,
+                IndexError,
+                UnicodeDecodeError,
+            ):
                 error_msg = response.text or f"HTTP {response.status_code}"
 
             raise httpx.HTTPStatusError(

tests/unit_tests/test_client.py

@@ -4,6 +4,7 @@
 from enum import StrEnum
 from typing import Any, Unpack
 
+import httpx
 import pytest
 from pydantic import SecretStr
 
@@ -261,6 +262,36 @@ def parameter_mappers(cls) -> list[ParameterMapper]:
         assert transformed == expected_output
 
 
+class TestHandleErrorResponse:
+    """Test ModalityClient._handle_error_response edge cases."""
+
+    @pytest.mark.parametrize(
+        "content",
+        [
+            b"\xff random binary",
+            b"\xff\xfe\x00\x00 utf-32-le bom",
+            b"\x80\x81\x82\x83",
+        ],
+        ids=["0xff-byte", "utf-32-le-bom", "high-bytes"],
+    )
+    def test_binary_error_body_raises_http_status_error(
+        self, text_model: Model, api_key: str, content: bytes
+    ) -> None:
+        """Binary error bodies produce HTTPStatusError, not UnicodeDecodeError (GH-170)."""
+        client = ConcreteModalityClient(
+            modality=Modality.TEXT,
+            model=text_model,
+            provider=text_model.provider,
+            auth=APIKey(secret=SecretStr(api_key)),
+        )
+        response = httpx.Response(
+            500, content=content, request=httpx.Request("POST", "https://api.test.com")
+        )
+
+        with pytest.raises(httpx.HTTPStatusError):
+            client._handle_error_response(response)
+
+
 class TestModalityClientStreaming:
     """Test ModalityClient._stream default behavior."""