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.

CLAUDE.md

@@ -101,10 +101,11 @@ Pass 2 builds `ok_disk_names` — the set of disk names that already match the s
 - `logs.py` — real-time log viewer fed from the stdout/stderr queue
 - `settings.py` — in-app editor for `config.json` (server URL, paths, credentials)
 
-**`_find_folder` (mods.py) — three-level name matching:** The mods view resolves a mod's local folder by mod name from `comparison.json`, which may differ from the server-canonical folder name used by the fetcher. Lookup order:
+**`_find_folder` (mods.py) — four-level name matching:** The mods view resolves a mod's local folder by mod name from `comparison.json`, which may differ from the server-canonical folder name used by the fetcher. Lookup order:
 1. Exact: `@{mod_name}`
 2. Case-insensitive: `@CBA_A3` matches `CBA_A3`
 3. Normalized (`_normalize_name`): strips all non-alphanumeric — handles punctuation/spacing differences, e.g. `@US GEAr- Units (IFA3)` matches `US GEAr: Units (IFA3)` (both → `usgearunitsifa3`)
+4. Steam ID via `meta.cpp`: reads `publishedid` from each folder's `meta.cpp` and matches against `mod["steam_id"]` — handles the case where the folder name bears no resemblance to the modlist name but the mod content is correct
 
 **`selection.json`** — GUI selection state file, tracked in git. Persists which mods/groups are selected between GUI sessions. Written by the GUI; safe to delete (GUI recreates it on next save).
 

gui/views/mods.py

@@ -7,7 +7,7 @@ from typing import TYPE_CHECKING, Optional
 
 import customtkinter as ctk
 
-from arma_modlist_tools.fetcher import _normalize_name
+from arma_modlist_tools.fetcher import _normalize_name, _parse_meta_cpp
 from gui._constants import COLOR_OK, COLOR_ERROR, COLOR_WARN, COLOR_RUNNING
 from gui.locales import t
 from gui.views.base import BaseView
@@ -16,13 +16,14 @@ if TYPE_CHECKING:
     from gui.app import ArmaModManagerApp
 
 
-def _find_folder(group_dir: Path, mod_name: str) -> Optional[Path]:
+def _find_folder(group_dir: Path, mod_name: str, steam_id: str | None = None) -> Optional[Path]:
     """Return the local mod folder path, or None if not downloaded.
 
     Matches in priority order:
     1. Exact folder name ``@{mod_name}``
     2. Case-insensitive name (handles ``@CBA_A3`` vs ``CBA_A3``)
     3. Normalized name — strips non-alphanumeric (handles ``@cba_a3`` vs ``CBA A3``)
+    4. Steam ID match via ``meta.cpp`` ``publishedid`` field (folder name differs from modlist name)
     """
     if not group_dir.is_dir():
         return None
@@ -38,6 +39,18 @@ def _find_folder(group_dir: Path, mod_name: str) -> Optional[Path]:
             return p
         if _normalize_name(p.name) == target_norm:
             return p
+    # Fallback: match by steam_id via meta.cpp when folder name diverges from modlist name
+    if steam_id:
+        for p in group_dir.iterdir():
+            if not p.is_dir():
+                continue
+            meta = p / "meta.cpp"
+            try:
+                sid = _parse_meta_cpp(meta.read_text(encoding="utf-8", errors="replace"))
+                if sid == steam_id:
+                    return p
+            except OSError:
+                pass
     return None
 
 
@@ -215,7 +228,7 @@ class ModsView(BaseView):
         link_map: dict[str, bool],
     ) -> None:
         for i, mod in enumerate(sorted(mods, key=lambda m: m["name"].lower())):
-            folder_path = _find_folder(cfg.downloads / group, mod["name"])
+            folder_path = _find_folder(cfg.downloads / group, mod["name"], mod.get("steam_id"))
             downloaded  = folder_path is not None
             linked      = (link_map.get(folder_path.name.lower(), False)
                            if folder_path else False)

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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