[Rovey]

Why

#65 made runs and the logon apply refuse a PC with more than one NVIDIA GPU, and listed three places that did not: the window's Apply saved tune, gao --apply and the tray watchdog's re-apply. They write a saved tune without testing it, so with two cards they could write it to a card it was not made for.

What

• saved_tune_for(driver, gpu_id, nvidia_gpus, refusal): the count goes to decide_boot, which returns SeveralGpus first. Callers: the Apply button and gao --apply pass Nvml::DeviceCount(); the undervolt on the saved tune passes 1, because its run already refused before it began.
• Watchdog: a second NVIDIA GPU counts as another card (gpu_ok false). The tune is not put back; the refusal goes to boot.log and the short balloon (kSeveralGpusBalloon) is shown once.
• docs/development.md: the "not refused yet" part of the design-decision row now says what refuses.

An integrated Intel or AMD GPU is not counted by NVML, so a one-card PC is not affected; an unknown count (-1) does not refuse, as before.

Tests

• cmake --workflow --preset ci: builds with /W4 /WX; core_tests and app_tests pass. The count rules are covered by the existing decide_boot / several_gpus tests; saved_tune_for itself reads gao.json and has no unit test.
• Not on a PC with two cards (none available). On the RTX 5070 the count is 1, so Apply and the watchdog behave as before.

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