fix: preserve locked modifiers on ei backend

src/lib/platform/EiKeyState.cpp

@@ -97,8 +97,9 @@ bool EiKeyState::fakeCtrlAltDel()
 
 KeyModifierMask EiKeyState::pollActiveModifiers() const
 {
-  const auto xkbMask = xkb_state_serialize_mods(m_xkbState, XKB_STATE_MODS_EFFECTIVE);
+  const auto effectiveMask = xkb_state_serialize_mods(m_xkbState, XKB_STATE_MODS_EFFECTIVE);
-  return convertModMask(xkbMask);
+  const auto lockedMask = xkb_state_serialize_mods(m_xkbState, XKB_STATE_MODS_LOCKED);
+  return convertModMask(effectiveMask) | convertModMask(lockedMask, true);
 }
 
 std::int32_t EiKeyState::pollActiveGroup() const
@@ -112,7 +113,7 @@ void EiKeyState::pollPressedKeys(KeyButtonSet &) const
   return;
 }
 
-std::uint32_t EiKeyState::convertModMask(xkb_mod_mask_t xkbModMaskIn) const
+std::uint32_t EiKeyState::convertModMask(xkb_mod_mask_t xkbModMaskIn, bool mapMod2ToNumLock) const
 {
   // This is our own modifier mask, not xkb's.
   std::uint32_t modMaskOut = 0;
@@ -170,12 +171,12 @@ std::uint32_t EiKeyState::convertModMask(xkb_mod_mask_t xkbModMaskIn) const
       modMaskOut |= (1 << kKeyModifierBitAltGr);
     else if (strcmp(XKB_VMOD_NAME_LEVEL5, name) == 0)
       modMaskOut |= (1 << kKeyModifierBitLevel5Lock);
-    else if (strcmp(XKB_VMOD_NAME_NUM, name) == 0)
+    else if (strcmp(XKB_VMOD_NAME_NUM, name) == 0 || (mapMod2ToNumLock && strcmp(XKB_MOD_NAME_MOD2, name) == 0))
       modMaskOut |= (1 << kKeyModifierBitNumLock);
     else if (strcmp(XKB_VMOD_NAME_SCROLL, name) == 0)
       modMaskOut |= (1 << kKeyModifierBitScrollLock);
     else if ((strcmp(XKB_VMOD_NAME_META, name) == 0) || // virtual; the old meta (not the new meta/super/logo key)
-             (strcmp(XKB_MOD_NAME_MOD2, name) == 0) ||  // spare, sometimes mapped to num lock.
+             (!mapMod2ToNumLock && strcmp(XKB_MOD_NAME_MOD2, name) == 0) || // spare, sometimes mapped to num lock.
              (strcmp(XKB_MOD_NAME_MOD3, name) == 0) // spare, could be mapped to alt_r, caps lock, scroll lock, etc.
     )
       LOG_VERBOSE("modifier mask %s ignored", name);
@@ -346,11 +347,17 @@ void EiKeyState::updateXkbState(uint32_t keyval, bool isPressed)
 
 void EiKeyState::clearStaleModifiers()
 {
-  // Recreate the XKB state to clear stuck modifiers that happen when
+  const auto lockedMods = xkb_state_serialize_mods(m_xkbState, XKB_STATE_MODS_LOCKED);
-  // modifier keys are press on client and released on server
+  const auto lockedLayout = xkb_state_serialize_layout(m_xkbState, XKB_STATE_LAYOUT_LOCKED);
+
+  // Recreate the XKB state to clear stuck depressed modifiers that happen when
+  // modifier keys are pressed on the client and released on the server. Locked
+  // modifiers are real keyboard state; do not clear NumLock/CapsLock/ScrollLock
+  // during screen transitions.
   if (m_xkbState) {
     xkb_state_unref(m_xkbState);
   }
   m_xkbState = xkb_state_new(m_xkbKeymap);
+  xkb_state_update_mask(m_xkbState, 0, 0, lockedMods, 0, 0, lockedLayout);
 }
 } // namespace deskflow

src/lib/platform/EiKeyState.h

@@ -43,7 +43,7 @@ protected:
   void fakeKey(const Keystroke &keystroke) override;
 
 private:
-  std::uint32_t convertModMask(xkb_mod_mask_t xkbModMaskIn) const;
+  std::uint32_t convertModMask(xkb_mod_mask_t xkbModMaskIn, bool mapMod2ToNumLock = false) const;
   void assignGeneratedModifiers(std::uint32_t keycode, KeyMap::KeyItem &item);
 
   EiScreen *m_screen = nullptr;

src/unittests/platform/CMakeLists.txt

@@ -25,6 +25,16 @@ elseif(APPLE)
     WORKING_DIRECTORY "${CMAKE_BINARY_DIR}/src/lib/platform"
   )
 elseif(UNIX)
+  if(LIBEI_FOUND)
+    create_test(
+      NAME EiKeyStateTests
+      DEPENDS platform
+      LIBS base arch
+      SOURCE EiKeyStateTests.cpp
+      WORKING_DIRECTORY "${CMAKE_BINARY_DIR}/src/lib/platform"
+    )
+  endif()
+
   if (BUILD_X11_SUPPORT)
     create_test(
       NAME XWindowsClipboardTests

src/unittests/platform/EiKeyStateTests.cpp

@@ -0,0 +1,109 @@
+/*
+ * Deskflow -- mouse and keyboard sharing utility
+ * SPDX-FileCopyrightText: (C) 2026 Deskflow Developers
+ * SPDX-License-Identifier: GPL-2.0-only WITH LicenseRef-OpenSSL-Exception
+ */
+
+#include "EiKeyStateTests.h"
+
+#include "base/EventQueue.h"
+#include "deskflow/AppUtil.h"
+#include "deskflow/KeyTypes.h"
+#include "platform/EiKeyState.h"
+
+#include <QByteArray>
+#include <QTemporaryFile>
+
+#include <cstdint>
+
+namespace {
+class TestAppUtil : public AppUtil
+{
+public:
+  int run() override
+  {
+    return 0;
+  }
+
+  void startNode() override
+  {
+  }
+
+  std::vector<std::string> getKeyboardLayoutList() override
+  {
+    return {"en"};
+  }
+
+  std::string getCurrentLanguageCode() override
+  {
+    return "en";
+  }
+};
+
+const char TestKeymap[] = R"XKB(xkb_keymap {
+xkb_keycodes "test" {
+    minimum = 8;
+    maximum = 255;
+    <LFSH> = 50;
+    <NMLK> = 77;
+};
+xkb_types "test" {
+    type "ONE_LEVEL" {
+        modifiers = none;
+        level_name[Level1] = "Any";
+    };
+};
+xkb_compat "test" {
+    interpret Shift_L+AnyOfOrNone(all) {
+        action = SetMods(modifiers=Shift);
+    };
+    interpret Num_Lock+AnyOfOrNone(all) {
+        action = LockMods(modifiers=Mod2);
+    };
+};
+xkb_symbols "test" {
+    key <LFSH> { [ Shift_L ] };
+    key <NMLK> { [ Num_Lock ] };
+    modifier_map Shift { <LFSH> };
+    modifier_map Mod2 { <NMLK> };
+};
+};)XKB";
+
+// XKB keycodes for TestKeymap.
+constexpr std::uint32_t LeftShiftKeycode = 50;
+constexpr std::uint32_t NumLockKeycode = 77;
+} // namespace
+
+void EiKeyStateTests::initTestCase()
+{
+  m_arch.init();
+  m_log.setFilter(LogLevel::Level::Verbose);
+}
+
+void EiKeyStateTests::clearStaleModifiers_shiftDownAndNumLockOn_shiftClearedAndNumLockPreserved()
+{
+  TestAppUtil appUtil;
+  EventQueue eventQueue;
+  deskflow::EiKeyState keyState(nullptr, &eventQueue);
+
+  QTemporaryFile keymapFile;
+  QVERIFY(keymapFile.open());
+  const QByteArray keymapData = QByteArray::fromRawData(TestKeymap, sizeof(TestKeymap) - 1);
+  QCOMPARE(keymapFile.write(keymapData), keymapData.size());
+  QVERIFY(keymapFile.flush());
+  keyState.init(keymapFile.handle(), keymapFile.size());
+
+  keyState.updateXkbState(LeftShiftKeycode, true);
+  keyState.updateXkbState(NumLockKeycode, true);
+  keyState.updateXkbState(NumLockKeycode, false);
+
+  QVERIFY((keyState.pollActiveModifiers() & KeyModifierShift) != 0);
+  QVERIFY((keyState.pollActiveModifiers() & KeyModifierNumLock) != 0);
+
+  keyState.clearStaleModifiers();
+
+  QVERIFY((keyState.pollActiveModifiers() & KeyModifierShift) == 0);
+  QVERIFY((keyState.pollActiveModifiers() & KeyModifierNumLock) != 0);
+}
+
+QTEST_MAIN(EiKeyStateTests)

src/unittests/platform/EiKeyStateTests.h

@@ -0,0 +1,25 @@
+/*
+ * Deskflow -- mouse and keyboard sharing utility
+ * SPDX-FileCopyrightText: (C) 2026 Deskflow Developers
+ * SPDX-License-Identifier: GPL-2.0-only WITH LicenseRef-OpenSSL-Exception
+ */
+
+#pragma once
+
+#include "arch/Arch.h"
+#include "base/Log.h"
+
+#include <QTest>
+
+class EiKeyStateTests : public QObject
+{
+  Q_OBJECT
+
+private Q_SLOTS:
+  void initTestCase();
+  void clearStaleModifiers_shiftDownAndNumLockOn_shiftClearedAndNumLockPreserved();
+
+private:
+  Arch m_arch;
+  Log m_log;
+};