fix: match mod folder by steam_id when folder name diverges from modlist name

_find_folder in mods.py now has a fourth fallback: reads publishedid from
meta.cpp inside each candidate folder and matches against mod["steam_id"].
Fixes mods appearing as "not downloaded" when the folder name on disk differs
from the name in the modlist but the mod content (meta.cpp) is correct.

Also adds 8 tests covering all four match strategies and edge cases.

test_suite.py

@@ -2229,6 +2229,128 @@ test("live: list_mod_files entries are (rel_path, url, size) tuples",  _test_liv
 test("live: find_mod_folder name fallback works (no steam_id)",        _test_live_find_mod_by_name_fallback)
 
 
+# ---------------------------------------------------------------------------
+# gui.views.mods — _find_folder
+# ---------------------------------------------------------------------------
+
+group("gui.views.mods — _find_folder")
+
+import importlib.util as _mods_ilu
+
+_mods_spec = _mods_ilu.spec_from_file_location(
+    "gui.views.mods", Path(__file__).parent / "gui" / "views" / "mods.py"
+)
+_mods_mod = _mods_ilu.module_from_spec(_mods_spec)
+# Stub out customtkinter and gui imports so the module loads without a display
+import types as _types
+import sys as _sys
+
+for _stub in ("customtkinter", "gui", "gui._constants", "gui.locales",
+              "gui.views", "gui.views.base"):
+    if _stub not in _sys.modules:
+        _sys.modules[_stub] = _types.ModuleType(_stub)
+
+# Provide the colour constants the module references at import time
+_sys.modules["gui._constants"].COLOR_OK      = "#4CAF50"
+_sys.modules["gui._constants"].COLOR_ERROR   = "#F44336"
+_sys.modules["gui._constants"].COLOR_WARN    = "#FF9800"
+_sys.modules["gui._constants"].COLOR_RUNNING = "#2196F3"
+
+# Stub BaseView so the class body does not fail
+_base_stub = _sys.modules["gui.views.base"] = _types.ModuleType("gui.views.base")
+_base_stub.BaseView = object
+
+# Stub locales.t so string calls don't crash
+_sys.modules["gui.locales"].t = lambda key, **kw: key
+
+_mods_spec.loader.exec_module(_mods_mod)
+_find_folder_fn = _mods_mod._find_folder
+
+
+def _test_ff_returns_none_for_missing_group(tmp_path):
+    assert _find_folder_fn(tmp_path / "nonexistent", "MyMod") is None
+
+
+def _test_ff_exact_match(tmp_path):
+    (tmp_path / "@MyMod").mkdir()
+    result = _find_folder_fn(tmp_path, "MyMod")
+    assert result == tmp_path / "@MyMod"
+
+
+def _test_ff_case_insensitive_match(tmp_path):
+    (tmp_path / "@mymod").mkdir()
+    result = _find_folder_fn(tmp_path, "MyMod")
+    assert result == tmp_path / "@mymod"
+
+
+def _test_ff_normalized_match(tmp_path):
+    # Folder on disk uses underscores; modlist name uses spaces — both normalize to same string
+    (tmp_path / "@My_Mod_Edition").mkdir()
+    result = _find_folder_fn(tmp_path, "My Mod Edition")
+    assert result == tmp_path / "@My_Mod_Edition"
+
+
+def _test_ff_steam_id_fallback(tmp_path):
+    """Folder name bears no resemblance to mod name but meta.cpp has correct ID."""
+    folder = tmp_path / "@ServerCanonicalName"
+    folder.mkdir()
+    (folder / "meta.cpp").write_text('publishedid = 123456789;\nname = "Some Mod";\n')
+    result = _find_folder_fn(tmp_path, "Completely Different Name", steam_id="123456789")
+    assert result == folder
+
+
+def _test_ff_steam_id_no_false_positive(tmp_path):
+    """Wrong steam_id in meta.cpp must not match."""
+    folder = tmp_path / "@WrongMod"
+    folder.mkdir()
+    (folder / "meta.cpp").write_text('publishedid = 999999999;\n')
+    result = _find_folder_fn(tmp_path, "My Mod", steam_id="123456789")
+    assert result is None
+
+
+def _test_ff_steam_id_skipped_when_none(tmp_path):
+    """No steam_id supplied → meta.cpp is never read (no false positives)."""
+    folder = tmp_path / "@SomeFolder"
+    folder.mkdir()
+    (folder / "meta.cpp").write_text('publishedid = 123456789;\n')
+    result = _find_folder_fn(tmp_path, "My Mod", steam_id=None)
+    assert result is None
+
+
+def _test_ff_missing_meta_cpp_skipped(tmp_path):
+    """Folders without meta.cpp are silently skipped in the steam_id pass."""
+    folder = tmp_path / "@NoMeta"
+    folder.mkdir()
+    result = _find_folder_fn(tmp_path, "My Mod", steam_id="123456789")
+    assert result is None
+
+
+# Wrap tmp_path calls in lambdas that supply a temp dir
+def _with_tmp(fn):
+    def wrapper():
+        with tempfile.TemporaryDirectory() as d:
+            fn(Path(d))
+    return wrapper
+
+
+test("_find_folder: None when group dir missing",
+     _with_tmp(_test_ff_returns_none_for_missing_group))
+test("_find_folder: exact @ModName match",
+     _with_tmp(_test_ff_exact_match))
+test("_find_folder: case-insensitive name match",
+     _with_tmp(_test_ff_case_insensitive_match))
+test("_find_folder: normalized name match (punctuation differs)",
+     _with_tmp(_test_ff_normalized_match))
+test("_find_folder: steam_id fallback via meta.cpp",
+     _with_tmp(_test_ff_steam_id_fallback))
+test("_find_folder: wrong steam_id in meta.cpp is not a match",
+     _with_tmp(_test_ff_steam_id_no_false_positive))
+test("_find_folder: no steam_id supplied → meta.cpp not checked",
+     _with_tmp(_test_ff_steam_id_skipped_when_none))
+test("_find_folder: missing meta.cpp silently skipped",
+     _with_tmp(_test_ff_missing_meta_cpp_skipped))
+
+
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 # Summary
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