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/corebin/cache_test.go

@@ -3,7 +3,10 @@ package corebin
 import (
 	"os"
 	"path/filepath"
+	"sync"
+	"sync/atomic"
 	"testing"
+	"time"
 )
 
 func TestResolveTrustsCacheWithoutStat(t *testing.T) {
@@ -35,6 +38,36 @@ func TestResolveTrustsCacheWithoutStat(t *testing.T) {
 	}
 }
 
+func TestResolveSingleflight(t *testing.T) {
+	Invalidate()
+	key := CacheKey(t.TempDir(), "naive")
+	var calls atomic.Int32
+	var started sync.WaitGroup
+	started.Add(1)
+	fn := func() (string, error) {
+		calls.Add(1)
+		started.Wait()
+		time.Sleep(20 * time.Millisecond)
+		return "embedded-test-core", nil
+	}
+	var wg sync.WaitGroup
+	for i := 0; i < 8; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			if _, err := Resolve(key, fn); err != nil {
+				t.Errorf("resolve: %v", err)
+			}
+		}()
+	}
+	time.Sleep(10 * time.Millisecond)
+	started.Done()
+	wg.Wait()
+	if calls.Load() != 1 {
+		t.Fatalf("expected 1 cold resolve, got %d", calls.Load())
+	}
+}
+
 func TestVirtualEmbeddedAWG(t *testing.T) {
 	Invalidate()
 	key := CacheKey("/bin", "awg")