On a Wayland HDR session, colors flickered between HDR and washed-out SDR every ~5 seconds: the mpv-leg timeout in apply_hdr_state was armed after SetHdrOutput returned, so a synchronous reply (the no-op short-circuit that runs on every playback restart and re-describe) orphaned the timer. Five seconds later it fired against a healthy plane and withdrew the live HDR image description; the next re-apply re-attached it and armed the next orphan.
Arm the timeout only while the reply is genuinely outstanding. An asynchronous reply still removes it, and a genuinely wedged core is still bounded.
Verified in a headless-sway Docker repro against the same PQ/BT.2020 file: 2.15.0 logs the false 'mpv never answered the output colour-space switch' warning 5 s after plane bring-up and again after source recognition; the fixed build logs none across bring-up, HDR playback, and seeks.
close#2016
edde746
4b6533d25b