test: make the backend suite pass on Windows

The new informational Windows job surfaced 91 failures: four real bugs (fixed in
the previous two commits) and a long tail of POSIX assumptions in the tests
themselves. None of them assert behaviour that differs on Windows, so they are
fixed rather than skipped wherever the behaviour is the same:

* Path spelling: expectations built with `str(tmp_path)` are compared through an
  identity helper (`normalize_root_identity`) or the platform's separator, since
  the code hands out forward-slashed business paths while `str()` is native.
* Root labels: `_root_display_labels` prefixes the drive on Windows ("C: loras"),
  so label assertions compare the final path component or derive the expected
  label from the same helper.
* `~` expansion reads USERPROFILE (ntpath), not HOME; timer granularity rounds
  0.1s down; a case-only rename counts as "already named" via `os.path.normcase`.
* Genuinely POSIX-only strategies are skipped with a reason instead of failing:
  the headless clipboard fallback, dbus file-manager selection, xdg-open, and
  the case-fold index test that simulates a case-sensitive filesystem.

tests/routes/test_base_model_routes_smoke.py

@@ -932,8 +932,8 @@ def test_resolve_folder_answers_with_the_root_that_holds_the_directory(
             assert payload["folder"] == "recipes"
             assert payload["candidates"] == [
                 {
-                    "folder_path": str(primary / "recipes"),
-                    "root": str(primary),
+                    "folder_path": str(primary / "recipes").replace(os.sep, "/"),
+                    "root": str(primary).replace(os.sep, "/"),
                     "is_symlink": False,
                 }
             ]

tests/routes/test_filesystem_paths.py

@@ -175,6 +175,10 @@ async def test_validate_path_expands_user(tmp_path, monkeypatch):
     subdir = tmp_path / "subdir"
     subdir.mkdir()
     monkeypatch.setenv("HOME", str(tmp_path))
+    # ntpath.expanduser reads USERPROFILE (or HOMEDRIVE + HOMEPATH), never HOME.
+    monkeypatch.setenv("USERPROFILE", str(tmp_path))
+    monkeypatch.setenv("HOMEDRIVE", tmp_path.drive)
+    monkeypatch.setenv("HOMEPATH", str(tmp_path)[len(tmp_path.drive):])
 
     response, payload = await _validate(_make_handler(), "~/subdir")
 

tests/routes/test_misc_routes.py

@@ -47,6 +47,18 @@ def _json_payload(response) -> dict[str, Any]:
     return json.loads(text)
 
 
+def _expected_opener() -> str:
+    """The command the handler uses to open a path on this platform."""
+
+    return "explorer" if os.name == "nt" else "xdg-open"
+
+
+def _posix_only(reason: str):
+    """Mark a test that exercises the POSIX open strategy (xdg-open/dbus)."""
+
+    return pytest.mark.skipif(os.name == "nt", reason=reason)
+
+
 class FakeRequest:
     def __init__(self, *, json_data=None, query=None, method="POST"):
         self._json_data = json_data or {}
@@ -636,7 +648,7 @@ async def test_open_backup_location_uses_settings_directory(tmp_path, monkeypatc
     assert response.status == 200
     assert payload["success"] is True
     assert payload["path"] == str(backup_dir)
-    assert calls == [["xdg-open", str(backup_dir)]]
+    assert calls == [[_expected_opener(), str(backup_dir)]]
 
 
 @pytest.mark.asyncio
@@ -667,9 +679,10 @@ async def test_open_sidecar_location_opens_configured_root(tmp_path, monkeypatch
     assert payload["path"] == str(root)
     # Created on demand so the button works before any migration ran.
     assert root.is_dir()
-    assert calls == [["xdg-open", str(root)]]
+    assert calls == [[_expected_opener(), str(root)]]
 
 
+@_posix_only("the headless clipboard fallback is the POSIX strategy; Windows always has a shell")
 @pytest.mark.asyncio
 async def test_open_sidecar_location_headless_returns_clipboard_mode(tmp_path, monkeypatch):
     """Without a GUI session xdg-open cannot work; the handler must hand the
@@ -721,6 +734,7 @@ async def test_get_settings_includes_resolved_sidecar_root(tmp_path):
     assert payload["settings"]["sidecar_storage_root_in_repo"] is False
 
 
+@_posix_only("the headless clipboard fallback is the POSIX strategy; Windows always has a shell")
 @pytest.mark.asyncio
 async def test_open_settings_location_headless_returns_clipboard_mode(tmp_path, monkeypatch):
     """Without a GUI session xdg-open cannot work; the handler must hand the
@@ -774,7 +788,7 @@ async def test_open_settings_location_with_display_opens_folder(tmp_path, monkey
 
     assert response.status == 200
     assert payload["success"] is True
-    assert calls == [["xdg-open", str(settings_file.parent)]]
+    assert calls == [[_expected_opener(), str(settings_file.parent)]]
 
 
 @pytest.mark.asyncio
@@ -807,9 +821,10 @@ async def test_open_wildcards_location_creates_and_opens_directory(tmp_path, mon
     assert payload["success"] is True
     assert payload["path"] == str(wildcards_dir)
     assert wildcards_dir.is_dir()
-    assert calls == [["xdg-open", str(wildcards_dir)]]
+    assert calls == [[_expected_opener(), str(wildcards_dir)]]
 
 
+@_posix_only("dbus file-manager selection is Linux-only")
 @pytest.mark.asyncio
 async def test_open_file_location_linux_selects_via_dbus(tmp_path, monkeypatch):
     """On a Linux desktop the handler should ask the freedesktop FileManager1
@@ -849,6 +864,7 @@ async def test_open_file_location_linux_selects_via_dbus(tmp_path, monkeypatch):
     assert popen_calls == []
 
 
+@_posix_only("xdg-open is the Linux opener")
 @pytest.mark.asyncio
 async def test_open_file_location_linux_falls_back_to_xdg_open(tmp_path, monkeypatch):
     """When the FileManager1 DBus interface is unavailable, fall back to
@@ -877,9 +893,10 @@ async def test_open_file_location_linux_falls_back_to_xdg_open(tmp_path, monkeyp
 
     assert response.status == 200
     assert payload["success"] is True
-    assert popen_calls == [["xdg-open", str(tmp_path)]]
+    assert popen_calls == [[_expected_opener(), str(tmp_path)]]
 
 
+@_posix_only("the headless clipboard fallback is the POSIX strategy; Windows always has a shell")
 @pytest.mark.asyncio
 async def test_open_file_location_headless_returns_clipboard_mode(tmp_path, monkeypatch):
     """Without a GUI session there is no file manager to open; the handler
@@ -917,6 +934,7 @@ def _patch_linux_desktop(monkeypatch):
     monkeypatch.setattr("py.routes.handlers.misc_handlers._is_wsl", lambda: False)
 
 
+@_posix_only("file-manager reveal via dbus is Linux-only")
 @pytest.mark.asyncio
 async def test_open_model_sidecar_location_reveals_metadata_file(tmp_path, monkeypatch):
     """Centralized mode: the resolved .metadata.json is revealed selected,
@@ -985,7 +1003,7 @@ async def test_open_model_sidecar_location_falls_back_to_sidecar_dir(tmp_path, m
     assert response.status == 200
     assert payload["success"] is True
     assert payload["path"] == str(sidecar_dir)
-    assert popen_calls == [["xdg-open", str(sidecar_dir)]]
+    assert popen_calls == [[_expected_opener(), str(sidecar_dir)]]
 
 
 @pytest.mark.asyncio
@@ -1012,6 +1030,7 @@ async def test_open_model_sidecar_location_missing_sidecar_returns_404(tmp_path,
     assert payload["success"] is False
 
 
+@_posix_only("the headless clipboard fallback is the POSIX strategy; Windows always has a shell")
 @pytest.mark.asyncio
 async def test_open_model_sidecar_location_headless_returns_clipboard_mode(tmp_path, monkeypatch):
     model_file = tmp_path / "model.safetensors"

tests/routes/test_model_source_handlers.py

@@ -403,9 +403,7 @@ def test_find_matching_root_includes_other_roots(isolated_config_roots, tmp_path
     vae_root = tmp_path / "vae"
     isolated_config_roots.other_roots = [str(vae_root)]
 
-    assert model_source_handlers._find_matching_root(str(vae_root / "sub")) == str(
-        vae_root
-    )
+    assert model_source_handlers._find_matching_root(str(vae_root / "sub")) == str(vae_root).replace(os.sep, "/").replace(os.sep, "/")
 
 
 def test_find_matching_root_respects_path_boundaries(isolated_config_roots, tmp_path):