Release 3.8.2.5: cheaper idle UI poll and tighter hot paths.

Delta getState by rev, pause when hidden, cancellable background loops,
hostCache bounds, unlock PollUI around engine status, corebin singleflight,
PingAll worker pool.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/config/config.go

@@ -327,6 +327,7 @@ func WriteExample(path string) error {
 
 // Save writes config as indented JSON (atomic replace).
 func Save(path string, cfg Config) error {
+	InvalidateHostCache()
 	if err := cfg.Validate(); err != nil {
 		return err
 	}