Session detection already hands every backend the live session's env:
WAYLAND_DISPLAY from a socket scan, XDG_RUNTIME_DIR from the uid, the
session bus, XDG_CURRENT_DESKTOP, and Hyprland's instance signature. sway
was the exception — SWAYSOCK had to be INHERITED from the login shell, so
a systemd --user host that never saw one had no sway IPC at all: no
output enumeration, no capture chooser, no wlroots backend (its
is_available() keys off that very variable).
It is derivable, and by identity rather than guess: sway names its socket
sway-ipc.<uid>.<pid>.sock, and detection already knows the compositor
PID. Ladder: a valid inherited value, then the exact PID's socket, then
the newest one we own (a sway re-exec can leave the name pointing at a
PID we didn't see). None on river — the other wlroots desktop ships no
sway IPC, and saying so is what stops apply_session_env exporting a
SWAYSOCK that points at nothing.
Closes the session-env half of design/per-monitor-portal-capture.md §6
for a desktop-login host: nothing has to be exported for the host to find
its session.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
enricobuehlerandClaude Opus 5
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