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diff --git a/libs/basic_games/games/openmw_support/openmw_cfg.py b/libs/basic_games/games/openmw_support/openmw_cfg.py
new file mode 100644
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+++ b/libs/basic_games/games/openmw_support/openmw_cfg.py
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+"""
+openmw_cfg.py — generate the managed block of an ``openmw.cfg``.
+
+OpenMW does not use a separate VFS injector: it reads its mods directly from an
+ordered list of ``data=`` directories and loads plugins in the order of the
+``content=`` lines.  This module rewrites *only* the keys we own, leaving every
+other line (engine settings, comments, unrelated keys) untouched:
+
+    data=               asset/plugin search dirs; LATER entries override earlier
+    content=            ordered plugin load list (.esp/.esm/.omwaddon/.omwscripts)
+    groundcover=        grass/groundcover plugins (kept out of content= for perf)
+    fallback-archive=   .bsa archives; later entries override earlier
+
+It is deliberately pure standard library (no Qt / mobase) so it can be unit
+tested on its own and reused by the OpenMW game plugin.  The caller decides what
+goes into ``data_dirs`` — a single merged dir (Fluorine FUSE) or one entry per
+mod (native OpenMW VFS) — this module stays agnostic about that choice.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Iterable
+
+# Morrowind masters, in canonical load order.
+#
+# Do NOT list ``builtin.omwscripts`` here.  It is OpenMW's built-in Lua bundle,
+# shipped inside the engine's ``resources/vfs-mw`` and loaded *implicitly* by the
+# engine itself.  If we also emit ``content=builtin.omwscripts`` it ends up
+# specified twice across the config chain and OpenMW aborts on startup with
+# "Content file specified more than once: builtin.omwscripts. Aborting...".
+VANILLA_MASTERS: list[str] = [
+    "Morrowind.esm",
+    "Tribunal.esm",
+    "Bloodmoon.esm",
+]
+
+# Vanilla BSAs, always emitted as the lowest-priority fallback-archive entries.
+VANILLA_BSAS: list[str] = [
+    "Morrowind.bsa",
+    "Tribunal.bsa",
+    "Bloodmoon.bsa",
+]
+
+# Keys this module fully owns (lowercase, exact match).
+_MANAGED_KEYS = frozenset({"data", "content", "groundcover", "fallback-archive"})
+
+
+def escape_data_path(path: str) -> str:
+    """Quote/escape a path for a ``data=`` line.
+
+    openmw.cfg uses boost::filesystem quoting: ``&`` and ``"`` are escaped with a
+    leading ``&`` and the whole value is wrapped in double quotes.  This matches
+    AnyOldName3's MO2 exporter so paths containing spaces or quotes round-trip.
+    """
+    out = ['"']
+    for ch in path:
+        if ch in ("&", '"'):
+            out.append("&")
+        out.append(ch)
+    out.append('"')
+    return "".join(out)
+
+
+def _is_managed(line: str) -> bool:
+    s = line.strip()
+    if not s or s.startswith("#") or "=" not in s:
+        return False
+    return s.split("=", 1)[0].strip().lower() in _MANAGED_KEYS
+
+
+def _preserve_non_managed(cfg_path: Path) -> list[str]:
+    """Return existing cfg lines minus the keys we manage, trailing blanks trimmed."""
+    kept: list[str] = []
+    if cfg_path.is_file():
+        for raw in cfg_path.read_text(encoding="utf-8", errors="replace").splitlines():
+            if not _is_managed(raw):
+                kept.append(raw)
+    while kept and not kept[-1].strip():
+        kept.pop()
+    return kept
+
+
+def _dedup_preserving_order(
+    base: Iterable[str], extra: Iterable[str]
+) -> list[str]:
+    """Concatenate ``base`` then ``extra``, dropping case-insensitive duplicates."""
+    result: list[str] = []
+    seen: set[str] = set()
+    for item in (*base, *extra):
+        key = item.lower()
+        if key not in seen:
+            seen.add(key)
+            result.append(item)
+    return result
+
+
+def build_managed_block(
+    data_dirs: Iterable[Path | str],
+    content_plugins: Iterable[str],
+    groundcover_plugins: Iterable[str] = (),
+    fallback_archives: Iterable[str] = (),
+    *,
+    vanilla_masters: Iterable[str] = VANILLA_MASTERS,
+    vanilla_bsas: Iterable[str] = VANILLA_BSAS,
+) -> list[str]:
+    """Build the managed cfg lines (no I/O), in the order OpenMW expects."""
+    content = _dedup_preserving_order(vanilla_masters, content_plugins)
+    archives = _dedup_preserving_order(vanilla_bsas, fallback_archives)
+
+    block: list[str] = [""]  # blank separator from the preserved section
+    block += [f"data={escape_data_path(str(d))}" for d in data_dirs]
+    block += [f"content={c}" for c in content]
+    block += [f"groundcover={g}" for g in groundcover_plugins]
+    block += [f"fallback-archive={a}" for a in archives]
+    return block
+
+
+def write_openmw_cfg(
+    cfg_path: Path,
+    data_dirs: Iterable[Path | str],
+    content_plugins: Iterable[str],
+    groundcover_plugins: Iterable[str] = (),
+    fallback_archives: Iterable[str] = (),
+    *,
+    vanilla_masters: Iterable[str] = VANILLA_MASTERS,
+    vanilla_bsas: Iterable[str] = VANILLA_BSAS,
+    log_fn=None,
+) -> None:
+    """Rewrite the managed data=/content=/groundcover=/fallback-archive= block."""
+    _log = log_fn or (lambda _: None)
+    data_dirs = list(data_dirs)  # consumed twice (block + log); avoid generator exhaustion
+    kept = _preserve_non_managed(cfg_path)
+    block = build_managed_block(
+        data_dirs,
+        content_plugins,
+        groundcover_plugins,
+        fallback_archives,
+        vanilla_masters=vanilla_masters,
+        vanilla_bsas=vanilla_bsas,
+    )
+    cfg_path.parent.mkdir(parents=True, exist_ok=True)
+    cfg_path.write_text("\n".join(kept + block) + "\n", encoding="utf-8")
+    _log(f"  Wrote openmw.cfg: {len(data_dirs)} data dir(s) to {cfg_path}.")
+
+
+def restore_openmw_cfg(
+    cfg_path: Path,
+    data_dirs: Iterable[Path | str],
+    *,
+    vanilla_masters: Iterable[str] = VANILLA_MASTERS,
+    vanilla_bsas: Iterable[str] = VANILLA_BSAS,
+    log_fn=None,
+) -> None:
+    """Reset the managed block to vanilla-only (used on uninstall / 'clear')."""
+    _log = log_fn or (lambda _: None)
+    if not cfg_path.is_file():
+        return
+    kept = _preserve_non_managed(cfg_path)
+    block = build_managed_block(
+        data_dirs,
+        (),
+        (),
+        (),
+        vanilla_masters=vanilla_masters,
+        vanilla_bsas=vanilla_bsas,
+    )
+    cfg_path.write_text("\n".join(kept + block) + "\n", encoding="utf-8")
+    _log(f"  Restored openmw.cfg to vanilla content at {cfg_path}.")