diff --git a/frontend/js/pane-manager.js b/frontend/js/pane-manager.js
index 461ca02..43cf14a 100644
--- a/frontend/js/pane-manager.js
+++ b/frontend/js/pane-manager.js
@@ -371,8 +371,8 @@ function createPaneTabManager(paneId) {
           const payload = JSON.stringify({
             paneId: this.paneId, tabId: tab.id, index: idx
           });
-          e.dataTransfer.setData('application/obsigate-tab', payload);
-          e.dataTransfer.setData('text/plain', payload); // fallback for browser compat
+          // text/plain is universally supported across all browsers for drag-drop
+          e.dataTransfer.setData('text/plain', payload);
           e.dataTransfer.effectAllowed = 'move';
           el.classList.add('dragging');
         });
@@ -395,9 +395,9 @@ function createPaneTabManager(paneId) {
           e.preventDefault();
           e.stopPropagation(); // Prevent container handler from double-firing
           document.querySelectorAll('.tab-drop-indicator').forEach(d => d.remove());
+          const raw = e.dataTransfer.getData('text/plain');
+          if (!raw) return;
           try {
-            const raw = e.dataTransfer.getData('application/obsigate-tab');
-            if (!raw) return;
             const dragData = JSON.parse(raw);
             // Same pane — reorder
             if (dragData.paneId === this.paneId) {
@@ -796,39 +796,49 @@ const PaneManager = {
       const tabBar = container.querySelector('.tab-bar');
       if (tabBar) tabBar.classList.remove('drop-target');
 
-      // Try both data formats
-      let raw = e.dataTransfer.getData('application/obsigate-tab');
-      if (!raw) raw = e.dataTransfer.getData('text/plain');
+      // Get drag data (text/plain is universally supported)
+      const raw = e.dataTransfer.getData('text/plain');
+      console.log('[PaneManager] drop fired, raw data:', raw ? raw.substring(0, 80) : 'null');
+
       if (!raw) return;
+      let dragData;
+      try { dragData = JSON.parse(raw); } catch (e2) { console.log('[PaneManager] JSON parse error:', e2); return; }
+      if (dragData.paneId == null || dragData.tabId == null) { console.log('[PaneManager] missing paneId/tabId'); return; }
 
-      try {
-        const dragData = JSON.parse(raw);
-        if (dragData.paneId == null || dragData.tabId == null) return;
+      // Recalculate edge zone from drop coordinates
+      const rect = container.getBoundingClientRect();
+      const relX = e.clientX - rect.left;
+      const relY = e.clientY - rect.top;
+      const isSingle = !this.isSplit();
 
-        // Recalculate edge zone from drop coordinates
-        const rect = container.getBoundingClientRect();
-        const relX = e.clientX - rect.left;
-        const relY = e.clientY - rect.top;
-        const isSingle = !this.isSplit();
+      console.log('[PaneManager] drop at', relX.toFixed(0), relY.toFixed(0),
+        'rect', rect.width.toFixed(0), 'x', rect.height.toFixed(0),
+        'isSingle', isSingle, 'paneId', paneId, 'srcPane', dragData.paneId);
 
-        if (isSingle && relX > rect.width * 0.72) {
-          this.splitRight();
-          setTimeout(() => {
-            const newPaneId = this.panes.length - 1;
-            this.transferTab(dragData.paneId, dragData.tabId, newPaneId);
-          }, 200);
-        } else if (isSingle && relY > rect.height * 0.72) {
-          this.splitDown();
-          setTimeout(() => {
-            const newPaneId = this.panes.length - 1;
-            this.transferTab(dragData.paneId, dragData.tabId, newPaneId);
-          }, 200);
-        } else if (dragData.paneId !== paneId) {
-          // Cross-pane transfer (already in split mode, different panes)
-          this.transferTab(dragData.paneId, dragData.tabId, paneId);
-        }
-        // else: same pane, not edge — tab handler deals with reorder
-      } catch (e2) { console.debug('PaneManager drop error:', e2); }
+      if (isSingle && relX > rect.width * 0.72) {
+        console.log('[PaneManager] → splitRight');
+        this.splitRight();
+        // Transfer after DOM settles
+        const transfer = () => {
+          const newPaneId = this.panes.length - 1;
+          console.log('[PaneManager] transferring tab', dragData.tabId, 'to pane', newPaneId);
+          this.transferTab(dragData.paneId, dragData.tabId, newPaneId);
+        };
+        setTimeout(transfer, 200);
+      } else if (isSingle && relY > rect.height * 0.72) {
+        console.log('[PaneManager] → splitDown');
+        this.splitDown();
+        const transfer = () => {
+          const newPaneId = this.panes.length - 1;
+          this.transferTab(dragData.paneId, dragData.tabId, newPaneId);
+        };
+        setTimeout(transfer, 200);
+      } else if (dragData.paneId !== paneId) {
+        console.log('[PaneManager] → cross-pane transfer', dragData.paneId, '→', paneId);
+        this.transferTab(dragData.paneId, dragData.tabId, paneId);
+      } else {
+        console.log('[PaneManager] → same pane, no edge — letting tab handler deal');
+      }
     });
   },