consolidate device ID sanitization and strengthen isPerDeviceMode check

Move all sanitization (strip non-alphanumeric, truncate to 32, fallback
to DEFAULT) into setDeviceId() so it's consistent regardless of call
site. deviceId() now delegates to setDeviceId() and re-reads the
sanitized value.

isPerDeviceMode() now uses QFileInfo::isDir() as a positive filesystem
check — no extension-based heuristics. Tests updated to create real
temp directories instead of using synthetic paths.

src/keeshare/KeeShare.cpp

@@ -67,22 +67,23 @@ QString KeeShare::deviceId()
             // Last resort: use hostname
             id = QSysInfo::machineHostName();
         }
-        // Sanitize to [A-Za-z0-9] only
-        id.remove(QRegularExpression("[^A-Za-z0-9]"));
-        if (id.isEmpty()) {
-            id = "DEFAULT";
-        }
         setDeviceId(id);
+        // Re-read the sanitized value
+        id = config()->get(Config::KeeShare_DeviceId).toString();
     }
     return id;
 }
 
 void KeeShare::setDeviceId(const QString& id)
 {
-    // Sanitize to [A-Za-z0-9] only and enforce max length
+    // All sanitization consolidated here: strip non-alphanumeric, enforce max
+    // length, and fall back to DEFAULT if empty
     QString sanitized = id;
     sanitized.remove(QRegularExpression("[^A-Za-z0-9]"));
     sanitized.truncate(32);
+    if (sanitized.isEmpty()) {
+        sanitized = QStringLiteral("DEFAULT");
+    }
     config()->set(Config::KeeShare_DeviceId, sanitized);
 }
 

src/keeshare/KeeShareSettings.cpp

@@ -25,6 +25,7 @@
 #include "gui/DatabaseIcons.h"
 
 #include <QDataStream>
+#include <QFileInfo>
 #include <QTextCodec>
 #include <QXmlStreamWriter>
 
@@ -288,9 +289,7 @@ namespace KeeShareSettings
 
     bool Reference::isPerDeviceMode() const
     {
-        return !path.isEmpty()
-            && !path.endsWith(".kdbx", Qt::CaseInsensitive)
-            && !path.endsWith(".kdbx.share", Qt::CaseInsensitive);
+        return !path.isEmpty() && QFileInfo(path).isDir();
     }
 
     bool Reference::operator<(const Reference& other) const

tests/TestSharing.cpp

@@ -17,6 +17,7 @@
 
 #include "TestSharing.h"
 
+#include <QDir>
 #include <QTest>
 #include <QXmlStreamReader>
 
@@ -35,6 +36,14 @@ Q_DECLARE_METATYPE(KeeShareSettings::Certificate)
 void TestSharing::initTestCase()
 {
     QVERIFY(Crypto::init());
+    m_tempDir = new QTemporaryDir();
+    QVERIFY(m_tempDir->isValid());
+}
+
+void TestSharing::cleanupTestCase()
+{
+    delete m_tempDir;
+    m_tempDir = nullptr;
 }
 
 void TestSharing::testNullObjects()
@@ -192,18 +201,28 @@ void TestSharing::testPerDeviceMode_data()
     QTest::addColumn<QString>("path");
     QTest::addColumn<bool>("expectedPerDevice");
 
-    // Classic mode paths (file-based)
+    // Classic mode paths (file-based — don't need to exist on disk)
     QTest::newRow("kdbx file") << "/some/path/share.kdbx" << false;
     QTest::newRow("kdbx.share file") << "/some/path/share.kdbx.share" << false;
     QTest::newRow("KDBX uppercase") << "/some/path/share.KDBX" << false;
     QTest::newRow("KDBX.SHARE uppercase") << "/some/path/share.KDBX.SHARE" << false;
     QTest::newRow("empty path") << "" << false;
+    QTest::newRow("nonexistent path") << "/nonexistent/path/nowhere" << false;
 
-    // Per-device mode paths (directory-based)
-    QTest::newRow("directory path") << "/some/sync/dir" << true;
-    QTest::newRow("directory trailing slash") << "/some/sync/dir/" << true;
-    QTest::newRow("relative directory") << "sync/shared" << true;
-    QTest::newRow("directory with dots") << "/some/path.d/sync" << true;
+    // Per-device mode paths (real directories on disk)
+    auto base = m_tempDir->path();
+
+    QDir(base).mkpath("syncdir");
+    QTest::newRow("directory path") << base + "/syncdir" << true;
+
+    QDir(base).mkpath("syncdir_slash");
+    QTest::newRow("directory trailing slash") << base + "/syncdir_slash/" << true;
+
+    QDir(base).mkpath("sub/shared");
+    QTest::newRow("nested directory") << base + "/sub/shared" << true;
+
+    QDir(base).mkpath("path.d/sync");
+    QTest::newRow("directory with dots") << base + "/path.d/sync" << true;
 }
 
 void TestSharing::testPerDeviceModeImportExport()
@@ -228,16 +247,20 @@ void TestSharing::testPerDeviceModeImportExport_data()
     QTest::addColumn<bool>("expectedImporting");
     QTest::addColumn<bool>("expectedExporting");
 
+    auto base = m_tempDir->path();
+    QDir(base).mkpath("importexport");
+    auto dir = base + "/importexport";
+
     QTest::newRow("per-device sync imports")
-        << "/some/dir" << int(KeeShareSettings::SynchronizeWith) << true << true;
+        << dir << int(KeeShareSettings::SynchronizeWith) << true << true;
     QTest::newRow("per-device import only")
-        << "/some/dir" << int(KeeShareSettings::ImportFrom) << true << false;
+        << dir << int(KeeShareSettings::ImportFrom) << true << false;
     QTest::newRow("per-device export only")
-        << "/some/dir" << int(KeeShareSettings::ExportTo) << false << true;
+        << dir << int(KeeShareSettings::ExportTo) << false << true;
     QTest::newRow("classic file sync")
-        << "/some/dir/share.kdbx" << int(KeeShareSettings::SynchronizeWith) << true << true;
+        << dir + "/share.kdbx" << int(KeeShareSettings::SynchronizeWith) << true << true;
     QTest::newRow("inactive per-device")
-        << "/some/dir" << int(KeeShareSettings::Inactive) << false << false;
+        << dir << int(KeeShareSettings::Inactive) << false << false;
 }
 
 const QSharedPointer<Botan::RSA_PrivateKey> TestSharing::stubkey(int index)

tests/TestSharing.h

@@ -19,6 +19,7 @@
 #define KEEPASSXC_TESTSHARING_H
 
 #include <QObject>
+#include <QTemporaryDir>
 
 namespace Botan
 {
@@ -30,6 +31,7 @@ class TestSharing : public QObject
 
 private slots:
     void initTestCase();
+    void cleanupTestCase();
     void testNullObjects();
     void testKeySerialization();
     void testReferenceSerialization();
@@ -43,6 +45,7 @@ private slots:
 
 private:
     const QSharedPointer<Botan::RSA_PrivateKey> stubkey(int index = 0);
+    QTemporaryDir* m_tempDir = nullptr;
 };
 
 #endif // KEEPASSXC_TESTSHARING_H