Runnable now — the Linux standalone on a real desktop (ADR-0131)

Not hardware-gated for any one vendor, and it is the only functional check the Linux capture path has: no CI runner has a sound server with something playing, so capture_linux.rs is compiled and linted on every push and executed only here. The scope is the artifact that ships — the .tar.gz from a v* tag or a workflow_dispatch run, unpacked on a real desktop — not a cargo run, whose binary was linked against the box’s own glibc and says nothing about the runner’s. Plan 0214 Phase 6 runs this list on the Ubuntu box.

Run it from the graphical session, not over SSH — there is no user sound server to reach there — with music playing at a normal volume.

• It extracts and launches. Record whether chmod +x ritmolux was needed (the tar header carries the bit; packaging/linux/stage.sh asserts it), and the distribution, version and $XDG_SESSION_TYPE.
• F3’s audio line reads live PulseAudio 48000/2 @DEFAULT_MONITOR@, and the visuals react. The endpoint is the server’s special name because the simple API cannot ask what it resolved to; pactl get-default-sink names the sink behind it. A failed PulseAudio … line is a finding with its reason attached; unsupported means the wrong arm compiled.
• ~/.local/share/Ritmolux/ appears (capital R) and holds config.toml, the preset copy and diagnostics.log, whose capture column carries the same token.
• F toggles fullscreen. D moves to the next monitor, or is a no-op — expected under Wayland, where the compositor places windows. Recorded either way, not treated as a bug.
• The frame rate F3 shows, the adapter the # renderer adapter line of diagnostics.log names, and whether the tier auto-dropped. On a laptop with two GPUs, note which one wgpu picked; ritmolux --list-adapters prints the roster.
• Capture follows a change of default sink. Stop the app, switch the default output in the desktop’s sound settings (or pactl set-default-sink), relaunch: the bands move with what the new sink plays. A Bluetooth sink is worth one run, since that is what Plan 0120 Phase 1 probed against.
• Stopping the sound server mid-run degrades rather than hangs. systemctl --user restart pipewire-pulse while it runs: the capture column moves off live, the shell’s bounded recovery reopens @DEFAULT_MONITOR@, and closing the window afterwards exits at once.

Anything that fails becomes a backlog entry, not a silent fix.