Hardens the renderer auto-detect so users never need the manual
options (the anti-videogame-settings goal).
Ladder (phase 1): a failed start now walks one rung down instead of
jumping to GL — wgpu (default adapter) -> wgpu (opposite
PowerPreference) -> GL -> software. The alt rung exists because the
#542 family is an ADAPTER mixup, not a wgpu failure; its survival is
version-stamped at disarm time (renderer_wgpu_alt) so later starts arm
it directly. GL-rung failures continue to software through the
non-auto branch (the persisted 'gl' carries the 'auto-gl' sentinel
value; a user-picked gl arms the literal 'gl' — unambiguous).
Auto-degradations are version-keyed (renderer_auto_degraded): a new
build re-probes auto once, the ladder re-degrades within a start if
the stack is still broken; manual picks clear both markers.
Sentinel disarm reworked: was a fixed 5s timer that lost the race
against late startup crashes (#558's swapchain error loops forever);
now first real input / close request / clean exit, with a 30s
no-touch fallback. The 5s timer keeps only its DPR-persist duty.
User-picked 'software' no longer arms (it cannot fail to start).
Watchdog (phase 2, #555 diagnosis aid): background thread probes the
event loop's cross-thread dispatch latency every 2s (30s startup
grace, clamped against suspend, 10 consecutive >250ms probes flag
once). Detection only — never switches tiers; surfaces as the 'UI
Loop Latency' Diagnostics row + bundle line so field reports carry a
number. The #555 lag is renderer-independent, so this measures the
layer where it actually lives.
One msgid x7 (the degradation toast is now rung-generic).
cc
vicrodh
7d3fc2a3aa