applyFailoverWarmTargets ran on the manager's single scheduler goroutine
(Sync -> Tick), so a slow or hung PreloadModelByName call froze probing
and fail-back for every chain. Keep the watchdog pin synchronous but run
the preload loop in its own goroutine. Adds a seam (preloadModelByName)
so a unit test can substitute a blocking loader and assert the callback
still returns promptly.
Assisted-by: Claude:claude-opus-5-5
Warm local targets are pinned in the watchdog and preloaded. Switches
and target health are exported as metrics, skipped attempts as traces.
Assisted-by: Claude:claude-opus-5-5
Ettore Di Giacinto