WindowServer crash when moving window near left edge of external display

Steps to Reproduce:

1. Connect a MacBook Pro (lid closed) to a large external monitor.

2. Run the SDL3 testwm test application.

   git clone https://github.com/libsdl-org/SDL.git

   cmake -S . -B build -DBUILD_SHARED_LIBS=OFF -DSDL_TESTS=ON

   cmake --build build

   The testwm binary will be located in the build/test directory.

3. Move the application window around the left edge of the external display.

Observed Result: WindowServer crashes.

System Configuration:

MacBook Pro M3 Max, macOS Sequoia 15.6.1

LG GX9, 5120x2160 resolution, running at 165 Hz refresh rate

Lid closed, single external display

Panic Log:

panic(cpu 7 caller 0xfffffe0027f61d5c): "mismatched swapID's 6386399 vs 6386400\n" @UnifiedPipeline.cpp:14570 Debugger message: panic Memory ID: 0xff OS release type: User OS version: 24G90 Kernel version: Darwin Kernel Version 24.6.0: Mon Jul 14 11:30:55 PDT 2025; root:xnu-11417.140.69~1/RELEASE_ARM64_T6031 Fileset Kernelcache UUID: 8AA69CD2038CD2BAE2ED364428F4DBEA Kernel UUID: 75A21406-D046-3232-AA3F-085335D5C848 Boot session UUID: B949E839-683B-4DAF-BE42-4562758F976E iBoot version: iBoot-11881.140.96 iBoot Stage 2 version: iBoot-11881.140.96 secure boot?: YES roots installed: 0 Paniclog version: 14 KernelCache slide: 0x000000001e0ec000 KernelCache base: 0xfffffe00250f0000 Kernel slide: 0x000000001e0f4000 Kernel text base: 0xfffffe00250f8000 Kernel text exec slide: 0x000000001f870000 Kernel text exec base: 0xfffffe0026874000 mach_absolute_time: 0x64e7db3e6a9 Epoch Time: sec usec Boot : 0x68b207f0 0x00082ee7 Sleep : 0x68c1a51c 0x00048c6c Wake : 0x68c1a760 0x00039aa4 Calendar: 0x68c1b78d 0x0001776a

Zone info: Zone map: 0xfffffe1018000000 - 0xfffffe3618000000 . VM : 0xfffffe1018000000 - 0xfffffe15e4000000 . RO : 0xfffffe15e4000000 - 0xfffffe187e000000 . GEN0 : 0xfffffe187e000000 - 0xfffffe1e4a000000 . GEN1 : 0xfffffe1e4a000000 - 0xfffffe2416000000 . GEN2 : 0xfffffe2416000000 - 0xfffffe29e2000000 . GEN3 : 0xfffffe29e2000000 - 0xfffffe2fae000000 . DATA : 0xfffffe2fae000000 - 0xfffffe3618000000 Metadata: 0xfffffe393c010000 - 0xfffffe3945810000 Bitmaps : 0xfffffe3945810000 - 0xfffffe394c104000 Extra : 0 - 0

CORE 0 recently retired instr at 0xfffffe0026a407a0 CORE 1 recently retired instr at 0xfffffe0026a40798 CORE 2 recently retired instr at 0xfffffe0026a407a0 CORE 3 recently retired instr at 0xfffffe0026a407a0 CORE 4 recently retired instr at 0xfffffe0026a407a0 CORE 5 recently retired instr at 0xfffffe0026a407a0 CORE 6 recently retired instr at 0xfffffe0026a407a0 CORE 7 recently retired instr at 0xfffffe0026a3eefc CORE 8 recently retired instr at 0xfffffe0026a407a0 CORE 9 recently retired instr at 0xfffffe0026a407a0 CORE 10 recently retired instr at 0xfffffe0026a407a0 CORE 11 recently retired instr at 0xfffffe0026a407a0 CORE 12 recently retired instr at 0xfffffe0026a407a0 CORE 13 recently retired instr at 0xfffffe0026a407a0 TPIDRx_ELy = {1: 0xfffffe29e4ef5ee0 0: 0x0000000000001007 0ro: 0x000000016c59b0e0 } CORE 0 PVH locks held: None CORE 1 PVH locks held: None CORE 2 PVH locks held: None CORE 3 PVH locks held: None CORE 4 PVH locks held: None CORE 5 PVH locks held: None CORE 6 PVH locks held: None CORE 7 PVH locks held: None CORE 8 PVH locks held: None CORE 9 PVH locks held: None CORE 10 PVH locks held: None CORE 11 PVH locks held: None CORE 12 PVH locks held: None CORE 13 PVH locks held: None CORE 0: PC=0xfffffe0026abfa40, LR=0xfffffe0026ae4fc8, FP=0xfffffe65b8703980 CORE 1: PC=0x0000000193ae2730, LR=0x000000019389d108, FP=0x000000016f43e590 CORE 2: PC=0xfffffe0026911e84, LR=0xfffffe0026911e84, FP=0xfffffe65b850bed0 CORE 3: PC=0xfffffe0026911e84, LR=0xfffffe0026911e84, FP=0xfffffe65b8ee7ed0 CORE 4: PC=0xfffffe0026911e84, LR=0xfffffe0026911e84, FP=0xfffffe65b7eebed0 CORE 5: PC=0xfffffe0026a3ac1c, LR=0xfffffe0026a3ac18, FP=0xfffffe65b8c63e40 CORE 6: PC=0xfffffe0026911e84, LR=0xfffffe0026911e84, FP=0xfffffe65b7033ed0 CORE 7 is the one that panicked. Check the full backtrace for details. CORE 8: PC=0xfffffe0026a3ac1c, LR=0xfffffe0026a3ac18, FP=0xfffffe65b737be40 CORE 9: PC=0xfffffe0026911e84, LR=0xfffffe0026911e84, FP=0xfffffe65b8f1fed0 CORE 10: PC=0xfffffe0026911e84, LR=0xfffffe0026911e84, FP=0xfffffe65b7fe7ed0 CORE 11: PC=0xfffffe0026a3ac1c, LR=0xfffffe0026a3ac18, FP=0xfffffe65b870fe40 CORE 12: PC=0xfffffe0026911e84, LR=0xfffffe0026911e84, FP=0xfffffe65b80a7ed0 CORE 13: PC=0xfffffe0026a3ac1c, LR=0xfffffe0026a3ac18, FP=0xfffffe65b685fe40 Compressor Info: 6% of compressed pages limit (OK) and 16% of segments limit (OK) with 0 swapfiles and OK swap space Panicked task 0xfffffe23153cb940: 10375 pages, 28 threads: pid 406: WindowServer Panicked thread: 0xfffffe29e4ef5ee0, backtrace: 0xfffffe65b6f07210, tid: 5146 lr: 0xfffffe00268d53d4 fp: 0xfffffe65b6f072a0 lr: 0xfffffe0026a36da0 fp: 0xfffffe65b6f07310 lr: 0xfffffe0026a35114 fp: 0xfffffe65b6f073d0 lr: 0xfffffe002687f8b0 fp: 0xfffffe65b6f073e0 lr: 0xfffffe00268d5710 fp: 0xfffffe65b6f077b0 lr: 0xfffffe0027169290 fp: 0xfffffe65b6f077d0 lr: 0xfffffe0027f61d5c fp: 0xfffffe65b6f07850 lr: 0xfffffe0029186878 fp: 0xfffffe65b6f07880 lr: 0xfffffe00270bd2a0 fp: 0xfffffe65b6f078b0 lr: 0xfffffe00270bd5b0 fp: 0xfffffe65b6f07a40 lr: 0xfffffe0026a00194 fp: 0xfffffe65b6f07b60 lr: 0xfffffe00268dcd48 fp: 0xfffffe65b6f07c00 lr: 0xfffffe00268b2ed4 fp: 0xfffffe65b6f07c60 lr: 0xfffffe00268c6868 fp: 0xfffffe65b6f07cb0 lr: 0xfffffe00268c6c80 fp: 0xfffffe65b6f07da0 lr: 0xfffffe0026a29bbc fp: 0xfffffe65b6f07e50 lr: 0xfffffe0026a355a4 fp: 0xfffffe65b6f07f10 lr: 0xfffffe002687f8b0 fp: 0xfffffe65b6f07f20 lr: 0x000000018dc89c34 fp: 0x0000000000000000 Kernel Extensions in backtrace: com.apple.iokit.IOMobileGraphicsFamily(343.0)[6C8CFA29-99CD-39D4-81BC-2B0F147BE64F]@0xfffffe002917d860->0xfffffe00291a024f