Drag gesture recognizer accepts all pointers when any pointer is accepted (#82786)

packages/flutter/lib/src/gestures/monodrag.dart

@@ -365,6 +365,10 @@ abstract class DragGestureRecognizer extends OneSequenceGestureRecognizer {
           localPosition: correctedPosition.local,
         );
       }
+      // This acceptGesture might have been called only for one pointer, instead
+      // of all pointers. Resolve all pointers to `accepted`. This won't cause
+      // infinite recursion because an accepted pointer won't be accepted again.
+      resolve(GestureDisposition.accepted);
     }
   }
 

packages/flutter/test/gestures/drag_test.dart

@@ -1440,4 +1440,48 @@ void main() {
       logs.clear();
     },
   );
+
+  testGesture('Does not crash when one of the 2 pointers wins by default and is then released', (GestureTester tester) {
+    // Regression test for https://github.com/flutter/flutter/issues/82784
+
+    bool didStartDrag = false;
+    final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer()
+      ..onStart = (_) { didStartDrag = true; }
+      ..onEnd = (DragEndDetails details) {} // Crash triggers at onEnd.
+      ..dragStartBehavior = DragStartBehavior.down;
+    final TapGestureRecognizer tap = TapGestureRecognizer()..onTap = () {};
+    final TapGestureRecognizer tap2 = TapGestureRecognizer()..onTap = () {};
+
+    // The pointer1 is caught by drag and tap.
+    final TestPointer pointer1 = TestPointer(5);
+    final PointerDownEvent down1 = pointer1.down(const Offset(10.0, 10.0));
+    drag.addPointer(down1);
+    tap.addPointer(down1);
+    tester.closeArena(pointer1.pointer);
+    tester.route(down1);
+
+    // The pointer2 is caught by drag and tap2.
+    final TestPointer pointer2 = TestPointer(6);
+    final PointerDownEvent down2 = pointer2.down(const Offset(10.0, 10.0));
+    drag.addPointer(down2);
+    tap2.addPointer(down2);
+    tester.closeArena(pointer2.pointer);
+    tester.route(down2);
+
+    // The tap is disposed, leaving drag the default winner.
+    tap.dispose();
+
+    // Wait for microtasks to finish, during which drag claims victory.
+    tester.async.flushMicrotasks();
+    expect(didStartDrag, true);
+
+    // The pointer1 is released, leaving pointer2 drag's only pointer.
+    tester.route(pointer1.up());
+
+    drag.dispose();
+
+    // Passes if no crashes here.
+
+    tap2.dispose();
+  });
 }