feat(client): add _build_default_decoders helper for installed-extras probe

Author: lesnik512

src/httpware/client.py

@@ -45,6 +45,27 @@ def _default_pydantic_decoder() -> ResponseDecoder:
     return PydanticDecoder()
 
 
+def _build_default_decoders() -> tuple[ResponseDecoder, ...]:
+    """Construct the default decoder tuple based on installed extras.
+
+    Pydantic-first when both extras are present; either-only when only one is
+    installed; empty tuple when neither is installed. Imports the concrete
+    decoder modules lazily so missing extras never trip `find_spec`-guarded
+    import paths. Called by `AsyncClient.__init__` and `Client.__init__` when
+    `decoders=None` (the default).
+    """
+    decoders: list[ResponseDecoder] = []
+    if import_checker.is_pydantic_installed:
+        from httpware.decoders.pydantic import PydanticDecoder  # noqa: PLC0415 — lazy by design (Seam C)
+
+        decoders.append(PydanticDecoder())
+    if import_checker.is_msgspec_installed:
+        from httpware.decoders.msgspec import MsgspecDecoder  # noqa: PLC0415 — lazy by design (Seam C)
+
+        decoders.append(MsgspecDecoder())
+    return tuple(decoders)
+
+
 @contextlib.asynccontextmanager
 async def _httpx2_exception_mapper() -> AsyncIterator[None]:
     """Map httpx2 exceptions to httpware exceptions. Shared by AsyncClient._terminal and stream()."""

tests/test_client_construction.py

@@ -1,9 +1,13 @@
 """Tests for AsyncClient construction and ownership semantics."""
 
+from unittest.mock import patch
+
 import httpx2
 import pytest
 
 from httpware import AsyncClient
+from httpware.client import _build_default_decoders
+from httpware.decoders.msgspec import MsgspecDecoder
 from httpware.decoders.pydantic import PydanticDecoder
 
 
@@ -90,3 +94,38 @@ async def __call__(self, request, next) -> httpx2.Response:  # noqa: A002, ANN00
     client = AsyncClient(middleware=(_Tag(),))
     assert client._user_middleware == (client._user_middleware[0],)  # noqa: SLF001
     assert len(client._user_middleware) == 1  # noqa: SLF001
+
+
+def test_build_default_decoders_both_extras_installed() -> None:
+    result = _build_default_decoders()
+    assert len(result) == 2  # noqa: PLR2004
+    assert isinstance(result[0], PydanticDecoder)
+    assert isinstance(result[1], MsgspecDecoder)
+
+
+def test_build_default_decoders_pydantic_only() -> None:
+    with patch("httpware._internal.import_checker.is_msgspec_installed", False):
+        result = _build_default_decoders()
+    assert len(result) == 1
+    assert isinstance(result[0], PydanticDecoder)
+
+
+def test_build_default_decoders_msgspec_only() -> None:
+    with patch("httpware._internal.import_checker.is_pydantic_installed", False):
+        result = _build_default_decoders()
+    assert len(result) == 1
+    assert isinstance(result[0], MsgspecDecoder)
+
+
+def test_build_default_decoders_neither_installed() -> None:
+    with (
+        patch("httpware._internal.import_checker.is_pydantic_installed", False),
+        patch("httpware._internal.import_checker.is_msgspec_installed", False),
+    ):
+        result = _build_default_decoders()
+    assert result == ()
+
+
+def test_build_default_decoders_returns_tuple() -> None:
+    result = _build_default_decoders()
+    assert isinstance(result, tuple)