Linux traces put the remaining stroke latency in presentation queueing (the app's frame fits
in one refresh; the rest waits on the swap chain), and an NVIDIA user cured it by forcing
vsync off. Testers can now compare without rebuilding: PHOTOCRAFT_PRESENT_MODE (fifo,
mailbox, immediate, autovsync, autonovsync) and PHOTOCRAFT_FRAME_LATENCY (1-3), applied over
the platform default. Bad values are logged and ignored. The active mode is logged at start,
kept in GpuInfo.present and shown in every stroke trace line.
RTX 5090, Vulkan, 120 Hz: default autovsync/latency 1 waits 6 ms per 8.3 ms frame; mailbox
renders every 2.3 ms with 0.2 ms wait, so each vsync shows the newest frame.
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