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fix: use D-Bus auto-activation for AT-SPI bus in isolated sessions #14

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fix: use D-Bus auto-activation for AT-SPI bus in isolated sessions #14

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1 change: 1 addition & 0 deletions CHANGELOG.md
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Expand Up @@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
### Fixed

- Segfault on Python 3.14 caused by missing `argtypes` on variadic `ei_seat_bind_capabilities` ctypes call
- `accessibility_tree`, `find_ui_elements`, `wait_for_element`, `list_windows`, and `focus_window` now work in isolated virtual sessions on Fedora, Debian, Ubuntu, and any other distro that installs the AT-SPI bus launcher outside `/usr/lib` (e.g. `/usr/libexec`). Instead of executing a hardcoded path, the AT-SPI bus is now brought up via D-Bus auto-activation (`gdbus call org.a11y.Bus.GetAddress`), which defers binary-path resolution to `dbus-daemon` and the distro-provided service file. The registry daemon is auto-activated transparently when apps first touch the a11y bus, so no manual bootstrap is required. Thanks to @davidselassie for reporting the Fedora failure in [#8](https://github.com/isac322/kwin-mcp/pull/8).

## [0.7.0] - 2026-03-29

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31 changes: 22 additions & 9 deletions src/kwin_mcp/session.py
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Expand Up @@ -333,19 +333,32 @@ def _build_wrapper_script(self, config: SessionConfig) -> str:
return f"""\
echo "DBUS_SESSION_BUS_ADDRESS=$DBUS_SESSION_BUS_ADDRESS"

# Ensure all child processes are cleaned up on exit
# Ensure all child processes are cleaned up on exit.
# The AT-SPI bus launcher and registryd are started via D-Bus
# auto-activation below; they are terminated automatically when our
# isolated session bus exits (dbus-run-session tears the bus down on
# parent exit), so we only need to track KWin explicitly here.
cleanup() {{
kill $KWIN_PID $AT_SPI_PID 2>/dev/null
wait $KWIN_PID $AT_SPI_PID 2>/dev/null
kill $KWIN_PID 2>/dev/null
wait $KWIN_PID 2>/dev/null
}}
trap cleanup EXIT TERM INT HUP

# Start the AT-SPI accessibility bus.
# ATSPI_DBUS_IMPLEMENTATION is set in _build_env() to force dbus-daemon
# instead of dbus-broker (which reuses the host's AT-SPI bus).
/usr/lib/at-spi-bus-launcher --launch-immediately &
AT_SPI_PID=$!
sleep 0.2
# Bring up the AT-SPI accessibility bus via D-Bus auto-activation.
# Calling org.a11y.Bus.GetAddress makes dbus-daemon resolve the
# service file (/usr/share/dbus-1/services/org.a11y.Bus.service) and
# exec the launcher at whatever path the current distro uses — Arch
# /usr/lib, Fedora/Debian/Ubuntu /usr/libexec, Flatpak /app/libexec,
# etc. Hardcoding a path breaks on everything except Arch.
# ATSPI_DBUS_IMPLEMENTATION=dbus-daemon (set in _build_env) prevents
# dbus-broker from sharing the host's a11y bus.
# The registryd comes up on its own when apps first touch the a11y
# bus, so no manual bootstrap is needed here.
gdbus call --session \\
--dest=org.a11y.Bus \\
--object-path=/org/a11y/bus \\
--method=org.a11y.Bus.GetAddress >/dev/null 2>&1 || true
sleep 0.3

# Pre-set D-Bus activation environment BEFORE starting KWin.
# When KWin triggers portal auto-activation, portal-kde will get
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