test_envprovider: skip symlink assertion on Windows for venv-rooted python

The Windows link_binary guard intentionally returns the venv-rooted
source python.exe unchanged (since shimming it breaks CPython's
pyvenv.cfg discovery). The existing linked_binary.is_symlink() /
linked_binary.resolve() == sys.executable assertions therefore
don't apply on Windows — there is no managed shim to inspect. Gate
them behind not IS_WINDOWS and on Windows check instead that
loaded.loaded_abspath == sys.executable directly.

Author: claude

tests/test_envprovider.py

@@ -7,6 +7,7 @@
 from abxpkg import Binary, EnvProvider, PipProvider, SemVer
 from abxpkg.config import load_derived_cache
 from abxpkg.exceptions import BinaryUninstallError
+from abxpkg.windows_compat import IS_WINDOWS
 
 
 class TestEnvProvider:
@@ -136,9 +137,18 @@ def test_provider_with_install_root_links_loaded_binary_and_writes_derived_env(
             assert provider.bin_dir is not None
             assert provider.bin_dir.exists()
             assert loaded.loaded_respath == Path(sys.executable).resolve()
-            linked_binary = provider.bin_dir / "python3"
-            assert linked_binary.is_symlink()
-            assert linked_binary.resolve() == Path(sys.executable).resolve()
+            # Unix: ``_link_loaded_binary`` creates a managed symlink in
+            # ``bin_dir`` pointing to ``sys.executable``. Windows: venv-
+            # rooted ``python.exe`` is returned unchanged by
+            # ``link_binary`` because CPython's ``pyvenv.cfg`` discovery
+            # can't follow the linked path — no shim is written, and
+            # ``loaded_abspath`` is the real venv python.
+            if not IS_WINDOWS:
+                linked_binary = provider.bin_dir / "python3"
+                assert linked_binary.is_symlink()
+                assert linked_binary.resolve() == Path(sys.executable).resolve()
+            else:
+                assert loaded.loaded_abspath == Path(sys.executable)
 
             derived_env_path = install_root / "derived.env"
             cache = load_derived_cache(derived_env_path)