fix: sub-tab ruler drag creates local selection, separate from main

- Add isDraggingSubTabRef/subTabDragStartRef for section-tab drag
- Ctrl+Click on sub-tab ruler clears sub-tab selection
- Sub-tab mousedown: set playhead + start drag
- Sub-tab mousemove/mouseup: update st.selectionStart/End locally
- Section-tab selection doesn't affect main session selection

app/static/js/app.jsx

@@ -7321,6 +7321,8 @@ const App = () => {
   const rulerDragStartRef = useRef(null);
   const rulerAnchorRef = useRef(null);
   const isDraggingRulerRef = useRef(false);
+  const subTabDragStartRef = useRef(null);
+  const isDraggingSubTabRef = useRef(false);
   const handlePlayPauseRef = useRef(null);
   const currentTimeRef = useRef(currentTime);
   currentTimeRef.current = currentTime;
@@ -10829,9 +10831,28 @@ const App = () => {
     };
     document.addEventListener('mousemove', handleMouseMove);
     document.addEventListener('mouseup', handleMouseUp);
+    // Sub-tab ruler drag (section/editor tabs)
+    const handleSubTabMove = e => {
+      if (!isDraggingSubTabRef.current) return;
+      const wrapper = timelineWrapperRef.current;
+      if (!wrapper) return;
+      const rect = wrapper.getBoundingClientRect();
+      const sl = wrapper.scrollLeft;
+      const raw = Math.max(0, (e.clientX - rect.left + sl) / zoom);
+      const time = snapValueRef.current !== 'free' ? snapTime(raw, snapValueRef.current, bpmRef.current) : raw;
+      const anchor = subTabDragStartRef.current ?? 0;
+      setSubTabs(prev => prev.map(s => s.id === activeTabRef.current ? { ...s, selectionStart: Math.min(anchor, time), selectionEnd: Math.max(anchor, time) } : s));
+    };
+    const handleSubTabUp = () => {
+      if (isDraggingSubTabRef.current) { isDraggingSubTabRef.current = false; subTabDragStartRef.current = null; }
+    };
+    document.addEventListener('mousemove', handleSubTabMove);
+    document.addEventListener('mouseup', handleSubTabUp);
     return () => {
       document.removeEventListener('mousemove', handleMouseMove);
       document.removeEventListener('mouseup', handleMouseUp);
+      document.removeEventListener('mousemove', handleSubTabMove);
+      document.removeEventListener('mouseup', handleSubTabUp);
     };
   }, [zoom, maxDuration]);
 
@@ -16445,8 +16466,16 @@ const App = () => {
           const sl = wrapper.scrollLeft;
           const raw = Math.max(0, (e.clientX - rect.left + sl) / zoom);
           const t = snapValue !== 'free' ? snapTime(raw, snapValue, bpm) : raw;
+          if (e.ctrlKey) {
+            e.preventDefault();
+            e.stopPropagation();
+            setSubTabs(prev => prev.map(s => s.id === activeTab ? { ...s, selectionStart: null, selectionEnd: null } : s));
+            return;
+          }
           if (e.shiftKey) { e.preventDefault(); e.stopPropagation(); }
           handlePlayheadSet(t);
+          subTabDragStartRef.current = t;
+          isDraggingSubTabRef.current = true;
         },
         scrollLeft: scrollLeft,
         canvasRedrawCount: canvasRedrawCount