tests: prove DecodeError wrap is decoder-agnostic via msgspec

Seam-level test wires MsgspecDecoder into AsyncClient and asserts a
malformed-JSON response still surfaces as httpware.DecodeError with
exc.original carrying the underlying msgspec exception.

Author: lesnik512

tests/test_decoders_msgspec.py

@@ -1,8 +1,12 @@
 """Unit tests for httpware.decoders.msgspec.MsgspecDecoder."""
 
+from http import HTTPStatus
+
+import httpx2
 import msgspec
 import pytest
 
+from httpware import AsyncClient, DecodeError
 from httpware._internal import import_checker
 from httpware.decoders import ResponseDecoder
 from httpware.decoders.msgspec import MsgspecDecoder
@@ -48,3 +52,21 @@ def test_construction_raises_without_extra_via_monkeypatch(
     monkeypatch.setattr(import_checker, "is_msgspec_installed", False)
     with pytest.raises(ImportError, match="MsgspecDecoder requires the 'msgspec' extra"):
         MsgspecDecoder()
+
+
+async def test_msgspec_decoder_failures_wrap_as_decode_error_at_seam() -> None:
+    """Proves wrapping is decoder-agnostic: switching to MsgspecDecoder still yields DecodeError."""
+
+    def handler(request: httpx2.Request) -> httpx2.Response:
+        return httpx2.Response(HTTPStatus.OK, content=b"{not json", request=request)
+
+    transport = httpx2.MockTransport(handler)
+    client = AsyncClient(
+        httpx2_client=httpx2.AsyncClient(transport=transport),
+        decoder=MsgspecDecoder(),
+    )
+    with pytest.raises(DecodeError) as exc_info:
+        await client.get("https://example.test/x", response_model=_Item)
+    exc = exc_info.value
+    assert exc.model is _Item
+    assert isinstance(exc.original, (msgspec.DecodeError, msgspec.ValidationError))