A field reporter installed punktfunk-gamescope under a running host
and kept streaming SDR, with no error to explain it. The host probes
the gamescope binary once per process and caches the answer, because
a session's bit depth must be settled before the display exists - so
a build installed mid-run is never seen.
The install section listed a command for every distro and never
mentioned the restart. Add it, and name the two startup log lines
that tell the two states apart.
A SteamOS-style session (Valve's /usr/lib/steamos/gamescope-session, as
CachyOS ships it) never got --custom-refresh-rates, so Steam's
in-session display menu showed one refresh entry and no resolutions,
and games paced themselves to that single number.
The two gamescope-session-plus paths hand the set to the SCRIPT as
CUSTOM_REFRESH_RATES and let it build the flag. Valve's script has
never read that variable, and the PATH shim forwards only
PF_HDR_ARGS - so the flag reached no SteamOS session at all.
Chain refresh_rate_args into that drop-in's PF_HDR_ARGS, keyed on the
session's own mode like launch_session's `offered`. Split the list
formatting into a pure refresh_rate_list so the no-whitespace
invariant that the unquoted ${PF_HDR_ARGS} depends on has a test.