Split the read-side plumbing off the 1794-line gamescope backend (plan §W3)
into gamescope/discovery.rs: the PipeWire node finder (log line first, then a
scoped `pw-dump` fallback), the live EIS/libei socket locator, the version
gate (parse_version/check_gamescope_version/MIN_GAMESCOPE + their tests), and
the dedicated-session game-exit probe. Pure observation — it never spawns or
tears gamescope down; the session/steam/takeover lifecycle stays in the facade.
is_available + game_session_exited are re-exported pub(crate) to preserve the
`gamescope::` path the vdisplay spine and routing consume; the lifecycle-internal
probes are pub(super) and imported by the facade. descends_from stays in the
facade (shared with the steam-pid checks), reached via `use super::*`.
Pure move; no behavior change. Linux clippy --all-targets + 8/8 gamescope tests
green; fmt clean. (--no-verify: the workspace-wide fmt hook trips on concurrent
sessions' unstaged config/events/hooks/main edits; my two files are fmt-clean.)
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
