The bare spawn builds gamescope's argv itself. The two managed modes hand the
flags over indirectly — `gamescope-session-plus` through `GAMESCOPE_BIN` +
`PF_HDR_ARGS`, SteamOS through a PATH shim — and a session free to ignore
either would exec the distro's gamescope carrying none of them.
Half of that failure was already loud: HDR dies on the bit depth the Welcome
fixed before the display existed. The other half was silent. The host had been
told the compositor would paint the pointer, so it stopped painting one, and
nobody did — a stream that is correct in every respect except that it has no
cursor, which nothing in the logs would have said.
So both managed paths now read the running compositor's `/proc/<pid>/cmdline`
once its node appears, and refuse the session when a flag we passed is missing.
The plan is fixed by then (`cursor_blend` feeds the encoder open, which
precedes the display), so this session cannot be corrected in place; instead
the capability is latched off for the process and the spawn fails, and the
retry resolves a correct SDR host-composited session. One rejected attempt per
boot, then it converges.
Fails OPEN at every ambiguity: no flags expected, or no readable gamescope in
`/proc`, says nothing. And it accepts ANY running gamescope carrying the flags,
because a box commonly has a second one — the Nobara test box runs its own
game-mode `/usr/bin/gamescope --steam` beside ours. That leaves only false
PASSES possible, and the flag that matters cannot produce one:
`--pipewire-composite-cursor` exists nowhere but our patch set.
Two things fell out of writing it. `gamescope_argvs` matches argv[0]'s basename
with `ends_with`, not `==` — the old equality test would have missed our own
`punktfunk-gamescope`, which is what `current_gamescope_output_size` was
already scanning for. And `hdr-probe` gained a line for who paints the cursor,
the one capability with no symptom of its own until you compare two streams.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
enricobuehlerandClaude Opus 5
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