Summary
session_connect (and --default-live-session mode) crashes with SIGSEGV inside ei_seat_bind_capabilities on first call. Repro on a fresh KDE Plasma 6 Wayland session under Fedora 43 (Bazzite stable, May 2026 image).
Environment
- Distro: Bazzite stable (atomic Fedora 43, image
ghcr.io/ublue-os/bazzite:stable 44.20260508)
- Compositor: KDE Plasma 6 /
kwin_wayland (running)
- libei:
1.5.0-1.fc43
- libeis:
1.5.0-1.fc43
- Python:
3.14.3-2.fc43
- kwin-mcp:
0.7.0 (installed via pip into a venv with --system-site-packages to pick up Fedora's python3-cairo 1.28 + python3-gobject 3.54.5)
- a11y bus running (
org.a11y.Bus, org.freedesktop.a11y.Manager both present)
Repro
python3 -m venv --system-site-packages ~/kwin-venv
~/kwin-venv/bin/pip install kwin-mcp
~/kwin-venv/bin/kwin-mcp --default-live-session # stdio MCP server
# then send: initialize, notifications/initialized, tools/call session_connect
The handshake + tools/list work fine (returns 30 tools). The crash happens the moment session_connect is invoked.
Stack trace (coredumpctl)
Signal: 11 (SEGV)
#0 0x00007f1d816548e8 ei_seat_bind_capabilities (libei.so.1 + 0xd8e8)
#1 0x00007f1d81b64056 ffi_call_unix64 (libffi.so.8 + 0x8056)
#2 0x00007f1d81b5fd16 ffi_call_int.lto_priv.0 (libffi.so.8 + 0x3d16)
#3 0x00007f1d81b627ae ffi_call (libffi.so.8 + 0x67ae)
#4 0x00007f1d81b9904b _ctypes_callproc (_ctypes.cpython-314 + 0x1104b)
#5 0x00007f1d81b8b118 PyCFuncPtr_call.cold (_ctypes.cpython-314 + 0x3118)
#6 0x00007f1d92d6fdbc _PyObject_Call (libpython3.14.so.1.0 + 0x263dbc)
The crash is inside libei itself, called via raw ctypes — suggests the ctypes signature / caller assumptions in kwin_mcp/input.py (or wherever the EI seat is set up) don't match what libei 1.5 expects. Most likely candidates:
ei_seat_bind_capabilities is being called with an invalid/NULL ei_seat* (seat not yet ready in 1.5's lifecycle).- The capabilities argument's bit layout changed between libei 1.3/1.4 and 1.5.
- The seat needs an explicit handshake step (e.g.
ei_seat_add_listener / wait for "added" event) before bind, that older versions tolerated being skipped.
Suggested fix
Switch from raw ctypes to pyei (python3-pyei is in Fedora and tracks libei) or wait for the seat-added event before calling ei_seat_bind_capabilities. Happy to test patches.
Workaround (for users hitting this)
Disable kwin-mcp until fixed. Fall back to ydotool (kernel uinput) for mouse/keyboard or libei via libei's own client tools.
Summary
session_connect(and--default-live-sessionmode) crashes with SIGSEGV insideei_seat_bind_capabilitieson first call. Repro on a fresh KDE Plasma 6 Wayland session under Fedora 43 (Bazzite stable, May 2026 image).Environment
ghcr.io/ublue-os/bazzite:stable44.20260508)kwin_wayland(running)1.5.0-1.fc431.5.0-1.fc433.14.3-2.fc430.7.0(installed viapipinto a venv with--system-site-packagesto pick up Fedora'spython3-cairo1.28 +python3-gobject3.54.5)org.a11y.Bus,org.freedesktop.a11y.Managerboth present)Repro
The handshake +
tools/listwork fine (returns 30 tools). The crash happens the momentsession_connectis invoked.Stack trace (coredumpctl)
The crash is inside libei itself, called via raw ctypes — suggests the ctypes signature / caller assumptions in
kwin_mcp/input.py(or wherever the EI seat is set up) don't match what libei 1.5 expects. Most likely candidates:ei_seat_bind_capabilitiesis being called with an invalid/NULLei_seat*(seat not yet ready in 1.5's lifecycle).ei_seat_add_listener/ wait for "added" event) before bind, that older versions tolerated being skipped.Suggested fix
Switch from raw ctypes to
pyei(python3-pyeiis in Fedora and tracks libei) or wait for the seat-added event before callingei_seat_bind_capabilities. Happy to test patches.Workaround (for users hitting this)
Disable kwin-mcp until fixed. Fall back to ydotool (kernel uinput) for mouse/keyboard or libei via
libei's own client tools.