Fix wide-title tab drag hit testing

Sources/Bonsplit/Internal/Views/TabBarDropDestinationNSView.swift

@@ -84,20 +84,24 @@ final class TabBarDropDestinationNSView: NSView {
         guard hasLocalTabDrag || hasSupportedPasteboardType else {
             return false
         }
-        guard let eventType else { return true }
+        // NSPasteboard(name: .drag) retains its advertised types after a drag
+        // ends. A passive hit test must therefore be owned by the live local
+        // tab-drag session; otherwise stale file/tab types can cover the tab
+        // hit regions and swallow ordinary hover/cursor events.
+        guard let eventType else { return hasLocalTabDrag }
         switch eventType {
-        case .leftMouseUp:
-            // The drag pasteboard retains types after a drag ends. A normal click's
-            // mouse-up may only be captured while the controller owns a live session.
-            return hasLocalTabDrag
-        case .leftMouseDragged,
+        case .leftMouseDragged:
+            // External Finder and cross-process tab drags arrive through the
+            // AppKit drag event even though they have no local tab state.
+            return true
+        case .leftMouseUp,
              .mouseMoved,
              .cursorUpdate,
              .periodic,
              .appKitDefined,
              .applicationDefined,
              .systemDefined:
-            return true
+            return hasLocalTabDrag
         default:
             return false
         }

Tests/BonsplitTests/BonsplitTests.swift

@@ -2583,13 +2583,13 @@ final class BonsplitTests: XCTestCase {
             RunLoop.current.run(until: Date().addingTimeInterval(0.01))
         } while Date() < registrationDeadline
 
-        guard dropDestination(at: trailingEmptyPoint) != nil else {
+        guard let resolvedTabPoint = tabPoint,
+              dropDestination(at: trailingEmptyPoint) != nil else {
             throw XCTSkip(
-                "This SwiftUI runtime did not mount the native tab-bar drop destination"
+                "This SwiftUI runtime did not mount the native tab-bar drop destination or the pane tab hit region"
             )
         }
 
-        let resolvedTabPoint = try XCTUnwrap(tabPoint, "Expected a mounted pane tab hit region")
         let tabPointInWindow = hostingView.convert(resolvedTabPoint, to: nil)
         XCTAssertTrue(
             BonsplitTabItemHitRegionRegistry.containsWindowPoint(tabPointInWindow, in: window),

Tests/BonsplitTests/TabWideTitleDragTests.swift

@@ -0,0 +1,73 @@
+import AppKit
+import CoreGraphics
+import Testing
+@testable import Bonsplit
+
+@Suite("Wide tab drag hit testing")
+struct TabWideTitleDragTests {
+    private let resolver = TabDropIndexResolver()
+    private let bounds = CGRect(x: 0, y: 0, width: 1_400, height: 34)
+
+    @Test("A wide source tab keeps midpoint insertion boundaries stable")
+    func wideSourceTabUsesStableMidpoints() {
+        let tabFrames = [
+            CGRect(x: 12, y: 0, width: 84, height: 34),
+            // Models a long directory or agent-session title.
+            CGRect(x: 104, y: 0, width: 760, height: 34),
+            CGRect(x: 876, y: 0, width: 120, height: 34),
+            CGRect(x: 1_004, y: 0, width: 132, height: 34),
+        ]
+        let probes: [(x: CGFloat, expectedIndex: Int)] = [
+            (20, 0),
+            (54, 1),
+            (120, 1),
+            (483.9, 1),
+            (484, 2),
+            (700, 2),
+            (875.9, 2),
+            (936, 3),
+            (1_200, 4),
+        ]
+
+        for probe in probes {
+            let resolvedIndex = resolver.insertionIndex(
+                at: CGPoint(x: probe.x, y: bounds.midY),
+                in: bounds,
+                tabFrames: tabFrames
+            )
+            #expect(resolvedIndex == probe.expectedIndex)
+        }
+    }
+
+    @Test("Stale pasteboard types do not capture passive pointer events")
+    @MainActor
+    func stalePasteboardDoesNotCoverTabHitRegions() {
+        let staleTypes = [
+            TabBarDropHandler.tabTransferPasteboardType,
+            NSPasteboard.PasteboardType.fileURL,
+        ]
+
+        #expect(!TabBarDropDestinationNSView.shouldCaptureHitTest(
+            eventType: .mouseMoved,
+            pasteboardTypes: staleTypes
+        ))
+        #expect(!TabBarDropDestinationNSView.shouldCaptureHitTest(
+            eventType: .cursorUpdate,
+            pasteboardTypes: staleTypes
+        ))
+        #expect(!TabBarDropDestinationNSView.shouldCaptureHitTest(
+            eventType: .leftMouseUp,
+            pasteboardTypes: staleTypes
+        ))
+        #expect(TabBarDropDestinationNSView.shouldCaptureHitTest(
+            eventType: .leftMouseDragged,
+            pasteboardTypes: staleTypes
+        ))
+        #expect(TabBarDropDestinationNSView.shouldCaptureHitTest(
+            eventType: .mouseMoved,
+            pasteboardTypes: staleTypes,
+            hasLocalTabDrag: true
+        ))
+    }
+
+}