monitor: keep workspace monitor bindings on full reconnect (#13384)

When all monitors disconnect, non-active workspaces could migrate to the wrong output after reconnect. Preserve workspace ownership and re-apply assigned monitor bindings on connect.

src/Compositor.cpp

@@ -3067,6 +3067,27 @@ void CCompositor::ensurePersistentWorkspacesPresent(const std::vector<SWorkspace
     }
 }
 
+void CCompositor::ensureWorkspacesOnAssignedMonitors() {
+    for (auto const& ws : getWorkspacesCopy()) {
+        if (!valid(ws) || ws->m_isSpecialWorkspace)
+            continue;
+
+        const auto RULE = g_pConfigManager->getWorkspaceRuleFor(ws);
+        if (RULE.monitor.empty())
+            continue;
+
+        const auto PMONITOR = getMonitorFromString(RULE.monitor);
+        if (!PMONITOR)
+            continue;
+
+        if (ws->m_monitor == PMONITOR)
+            continue;
+
+        Log::logger->log(Log::DEBUG, "ensureWorkspacesOnAssignedMonitors: moving workspace {} to {}", ws->m_name, PMONITOR->m_name);
+        moveWorkspaceToMonitor(ws, PMONITOR, true);
+    }
+}
+
 std::optional<unsigned int> CCompositor::getVTNr() {
     if (!m_aqBackend->hasSession())
         return std::nullopt;

src/Compositor.hpp

@@ -161,6 +161,7 @@ class CCompositor {
     void                                updateSuspendedStates();
     void                                onNewMonitor(SP<Aquamarine::IOutput> output);
     void                                ensurePersistentWorkspacesPresent(const std::vector<SWorkspaceRule>& rules, PHLWORKSPACE pWorkspace = nullptr);
+    void                                ensureWorkspacesOnAssignedMonitors();
     std::optional<unsigned int>         getVTNr();
     bool                                isVRRActiveOnAnyMonitor() const;
 

src/helpers/Monitor.cpp

@@ -82,7 +82,10 @@ void CMonitor::onConnect(bool noRule) {
     m_zoomAnimProgress->setValueAndWarp(0.F);
     m_zoomAnimFrameCounter = 0;
 
-    g_pEventLoopManager->doLater([] { g_pConfigManager->ensurePersistentWorkspacesPresent(); });
+    g_pEventLoopManager->doLater([] {
+        g_pConfigManager->ensurePersistentWorkspacesPresent();
+        g_pCompositor->ensureWorkspacesOnAssignedMonitors();
+    });
 
     m_listeners.frame      = m_output->events.frame.listen([this] {
         if (m_frameScheduler)
@@ -290,10 +293,16 @@ void CMonitor::onConnect(bool noRule) {
         if (!valid(ws))
             continue;
 
-        if (ws->m_lastMonitor == m_name || g_pCompositor->m_monitors.size() == 1 /* avoid lost workspaces on recover */) {
+        const auto CURRENTMON = ws->m_monitor.lock();
+        const bool ORPHANED   = !CURRENTMON || std::ranges::none_of(g_pCompositor->m_monitors, [&](const auto& mon) { return mon == CURRENTMON; });
+        const bool RETURNING  = ws->m_lastMonitor == m_name;
+        const bool RECOVERY   = g_pCompositor->m_monitors.size() == 1 && ORPHANED; // temporarily recover orphaned workspaces
+
+        if (RETURNING || RECOVERY) {
             g_pCompositor->moveWorkspaceToMonitor(ws, m_self.lock());
             g_pDesktopAnimationManager->startAnimation(ws, CDesktopAnimationManager::ANIMATION_TYPE_IN, true, true);
-            ws->m_lastMonitor = "";
+            if (RETURNING)
+                ws->m_lastMonitor = "";
         }
     }
 
@@ -429,19 +438,24 @@ void CMonitor::onDisconnect(bool destroy) {
     m_enabled             = false;
     m_renderingInitPassed = false;
 
+    std::vector<PHLWORKSPACE> wspToMove;
+    for (auto const& w : g_pCompositor->getWorkspaces()) {
+        if (w->m_monitor == m_self || !w->m_monitor)
+            wspToMove.emplace_back(w.lock());
+    }
+
+    // Preserve ownership across cascaded monitor disconnects.
+    // The first disconnected monitor "owns" where a workspace should return.
+    for (auto const& w : wspToMove) {
+        if (w && w->m_lastMonitor.empty())
+            w->m_lastMonitor = m_name;
+    }
+
     if (BACKUPMON) {
         // snap cursor
         g_pCompositor->warpCursorTo(BACKUPMON->m_position + BACKUPMON->m_transformedSize / 2.F, true);
 
-        // move workspaces
-        std::vector<PHLWORKSPACE> wspToMove;
-        for (auto const& w : g_pCompositor->getWorkspaces()) {
-            if (w->m_monitor == m_self || !w->m_monitor)
-                wspToMove.emplace_back(w.lock());
-        }
-
         for (auto const& w : wspToMove) {
-            w->m_lastMonitor = m_name;
             g_pCompositor->moveWorkspaceToMonitor(w, BACKUPMON);
             g_pDesktopAnimationManager->startAnimation(w, CDesktopAnimationManager::ANIMATION_TYPE_IN, true, true);
         }