Fix Steam game mode: strip LD_PRELOAD, robust looksValid(), restore env for games

Steam injects 32-bit gameoverlayrenderer.so via LD_PRELOAD which causes
"wrong ELF class" errors for 64-bit Qt6 apps. Save and clear LD_PRELOAD
in both launcher and AppRun scripts, restore it in ProtonLauncher for
game processes.

Also hardens looksValid() with QFileInfo::exists() for absolute paths
(QDir::exists() has edge cases with relative subdirectory paths), adds
case-insensitive directory walking fallback, and adds debug logging to
both looksValid() and detectGame().

Adds ~/.steam/debian-installation to Python steam_utils.py candidates.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

4 files changed, 61 insertions, 2 deletions

diff --git a/docker/build-inner.sh b/docker/build-inner.sh
index 484412b..2d32e31 100755
--- a/docker/build-inner.sh
+++ b/docker/build-inner.sh
@@ -362,10 +362,16 @@ HERE="$(cd "$(dirname "$SELF")" && pwd)"
 # Without this, our bundled LD_LIBRARY_PATH leaks into game processes and
 # causes library conflicts.
 export FLUORINE_ORIG_LD_LIBRARY_PATH="${LD_LIBRARY_PATH:-}"
+export FLUORINE_ORIG_LD_PRELOAD="${LD_PRELOAD:-}"
 export FLUORINE_ORIG_PATH="${PATH}"
 export FLUORINE_ORIG_XDG_DATA_DIRS="${XDG_DATA_DIRS:-/usr/local/share:/usr/share}"
 export FLUORINE_ORIG_QT_PLUGIN_PATH="${QT_PLUGIN_PATH:-}"
 
+# Steam injects 32-bit gameoverlayrenderer.so via LD_PRELOAD which causes
+# "wrong ELF class" errors for 64-bit Qt6 apps (see PrismLauncher #3421).
+# Clear it for our process; game launches restore via FLUORINE_ORIG_LD_PRELOAD.
+unset LD_PRELOAD
+
 # ── Sync entire app to ~/.local/share/fluorine/bin/ ──
 # This gives instances a stable symlink target that won't break if the user
 # moves or deletes the original tarball extraction directory.
@@ -630,10 +636,14 @@ BIN="${HERE}/usr/bin"
 APPIMAGE_DIR="$(dirname "$(readlink -f "${APPIMAGE:-$0}")")"
 
 export FLUORINE_ORIG_LD_LIBRARY_PATH="${LD_LIBRARY_PATH:-}"
+export FLUORINE_ORIG_LD_PRELOAD="${LD_PRELOAD:-}"
 export FLUORINE_ORIG_PATH="${PATH}"
 export FLUORINE_ORIG_XDG_DATA_DIRS="${XDG_DATA_DIRS:-/usr/local/share:/usr/share}"
 export FLUORINE_ORIG_QT_PLUGIN_PATH="${QT_PLUGIN_PATH:-}"
 
+# Steam injects 32-bit gameoverlayrenderer.so via LD_PRELOAD — clear it.
+unset LD_PRELOAD
+
 export PATH="${BIN}:${PATH}"
 # Replace (not append) LD_LIBRARY_PATH — Steam game mode injects its runtime
 # libs which break Python/Qt.  RPATH handles the binary's own deps.
diff --git a/libs/basic_games/steam_utils.py b/libs/basic_games/steam_utils.py
index f61f392..3babd55 100644
--- a/libs/basic_games/steam_utils.py
+++ b/libs/basic_games/steam_utils.py
@@ -164,6 +164,7 @@ def find_steam_path() -> Path | None:
     # Linux: check common Steam install locations.
     for candidate in (
         Path.home() / ".local" / "share" / "Steam",
+        Path.home() / ".steam" / "debian-installation",
         Path.home() / ".steam" / "steam",
         Path.home()
         / ".var"
diff --git a/libs/basic_games_native/src/basicgameplugin.cpp b/libs/basic_games_native/src/basicgameplugin.cpp
index 0631210..5f41f3a 100644
--- a/libs/basic_games_native/src/basicgameplugin.cpp
+++ b/libs/basic_games_native/src/basicgameplugin.cpp
@@ -4,6 +4,8 @@
 #include <uibase/utility.h>
 #include <uibase/versioninfo.h>
 
+#include <uibase/log.h>
+
 #include <QDateTime>
 #include <QDirIterator>
 #include <QStandardPaths>
@@ -87,6 +89,8 @@ void BasicGamePlugin::detectGame()
   for (int steamId : m_def.steamAppIds) {
     QString path = findSteamGamePath(steamId);
     if (!path.isEmpty()) {
+      MOBase::log::debug("detectGame: '{}' found via Steam appid {} at '{}'",
+                         m_def.gameName, steamId, path);
       setGamePath(path);
       return;
     }
@@ -315,9 +319,50 @@ int BasicGamePlugin::nexusGameID() const
 
 bool BasicGamePlugin::looksValid(QDir const& dir) const
 {
-  // Primary check: binary at game root
-  if (dir.exists(m_def.binaryName))
+  // Primary check: binary at game root.
+  // Use QFileInfo with the absolute path directly — QDir::exists() with
+  // relative paths containing subdirectories can have edge-case issues on
+  // some filesystems / Qt builds.
+  const QString absPath = dir.absoluteFilePath(m_def.binaryName);
+  if (QFileInfo::exists(absPath)) {
     return true;
+  }
+
+  // Case-insensitive fallback: Linux filesystems are case-sensitive but
+  // Steam sometimes creates directories with different casing than expected.
+  // Walk the path components and try case-insensitive matching.
+  if (m_def.binaryName.contains('/')) {
+    QStringList parts = QString(m_def.binaryName).replace('\\', '/').split('/');
+    QString current   = dir.absolutePath();
+    bool found        = true;
+    for (const QString& part : parts) {
+      QDir d(current);
+      if (d.exists(part)) {
+        current = d.absoluteFilePath(part);
+        continue;
+      }
+      // Try case-insensitive match
+      const QStringList entries =
+          d.entryList(QDir::Files | QDir::Dirs | QDir::NoDotAndDotDot);
+      bool matched = false;
+      for (const QString& entry : entries) {
+        if (entry.compare(part, Qt::CaseInsensitive) == 0) {
+          current = d.absoluteFilePath(entry);
+          matched = true;
+          break;
+        }
+      }
+      if (!matched) {
+        found = false;
+        break;
+      }
+    }
+    if (found) {
+      MOBase::log::debug("looksValid: found '{}' via case-insensitive match in '{}'",
+                         m_def.binaryName, dir.absolutePath());
+      return true;
+    }
+  }
 
   // Fallback: check if the data directory exists relative to this path.
   // Some UE5 games (e.g. Oblivion Remastered) have their root exe nested
@@ -334,6 +379,8 @@ bool BasicGamePlugin::looksValid(QDir const& dir) const
     }
   }
 
+  MOBase::log::debug("looksValid: '{}' not found in '{}'", m_def.binaryName,
+                     dir.absolutePath());
   return false;
 }
 
diff --git a/src/src/protonlauncher.cpp b/src/src/protonlauncher.cpp
index f25d355..57a88fc 100644
--- a/src/src/protonlauncher.cpp
+++ b/src/src/protonlauncher.cpp
@@ -70,6 +70,7 @@ void cleanAppImageEnv(QProcessEnvironment& env)
 
   const bool hasOrigVars = env.contains("FLUORINE_ORIG_PATH");
   restoreOrStrip("LD_LIBRARY_PATH", "FLUORINE_ORIG_LD_LIBRARY_PATH", env);
+  restoreOrStrip("LD_PRELOAD", "FLUORINE_ORIG_LD_PRELOAD", env);
   restoreOrStrip("PATH", "FLUORINE_ORIG_PATH", env);
   restoreOrStrip("XDG_DATA_DIRS", "FLUORINE_ORIG_XDG_DATA_DIRS", env);
   restoreOrStrip("QT_PLUGIN_PATH", "FLUORINE_ORIG_QT_PLUGIN_PATH", env);