fix: search ~/.steam/root and Flatpak data/Steam roots

Layouts from PR #1 (Manjaro report), folded into tools/steam_paths.py.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014TkQMhvEyoFqKzeCC69N6o

tests/test_steam_paths.py

@@ -93,6 +93,42 @@ def test_steam_root_without_vdf_still_works():
         )
 
 
+def test_legacy_steam_root_symlink():
+    with tempfile.TemporaryDirectory() as home:
+        steam = os.path.join(home, ".steam/root")
+        make_library(steam)
+        env = {"HOME": home}
+        check(
+            steam_paths.find_data_dir(env) == os.path.join(steam, "steamapps/common/Cosmoteer/Data"),
+            "~/.steam/root was not searched",
+        )
+
+
+def test_flatpak_data_dir_layout():
+    with tempfile.TemporaryDirectory() as home:
+        steam = os.path.join(home, ".var/app/com.valvesoftware.Steam/data/Steam")
+        make_library(steam)
+        env = {"HOME": home}
+        check(
+            steam_paths.find_mods_dir(env) == os.path.join(steam, PROTON_MODS),
+            "Flatpak XDG_DATA_HOME layout (.var/app/.../data/Steam) was not searched",
+        )
+
+
+def test_library_path_with_spaces():
+    with tempfile.TemporaryDirectory() as home:
+        steam = os.path.join(home, ".local/share/Steam")
+        second = os.path.join(home, "my games/Steam Library")
+        make_library(steam, with_game=False, with_mods=False)
+        make_library(second)
+        write_vdf(steam, [steam, second])
+        env = {"HOME": home}
+        check(
+            steam_paths.find_mods_dir(env) == os.path.join(second, PROTON_MODS),
+            "Library path containing spaces was not handled",
+        )
+
+
 def test_windows_profile_mods_dir():
     with tempfile.TemporaryDirectory() as profile:
         mods = os.path.join(profile, "Saved Games/Cosmoteer/76561190000000000/Mods")

tools/steam_paths.py

@@ -27,8 +27,10 @@ PROTON_PROFILE = "compatdata/" + APP_ID + "/pfx/drive_c/users/steamuser/Saved Ga
 STEAM_ROOTS_UNDER_HOME = [
     ".local/share/Steam",
     ".steam/steam",
+    ".steam/root",
     ".steam/debian-installation",
     ".var/app/com.valvesoftware.Steam/.local/share/Steam",
+    ".var/app/com.valvesoftware.Steam/data/Steam",
     ".snap/steam/common/.local/share/Steam",
     "snap/steam/common/.local/share/Steam",
 ]