perf(core): Detect Sentry executor thread without name scan (JAVA-607)

PersistingScopeObserver.serializeToDisk gated the on-executor fast path by
scanning Thread.currentThread().getName(), which allocates a String and
scans it on every scope mutation (breadcrumb, tag, trace, ...). Tag the
executor threads with a marker Thread subclass and expose an allocation-free
SentryExecutorService.isSentryExecutorThread() check instead.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: runningcode

sentry/api/sentry.api

@@ -3181,6 +3181,7 @@ public final class io/sentry/SentryExecutorService : io/sentry/ISentryExecutorSe
 	public fun <init> (Lio/sentry/SentryOptions;)V
 	public fun close (J)V
 	public fun isClosed ()Z
+	public static fun isSentryExecutorThread ()Z
 	public fun prewarm ()V
 	public fun schedule (Ljava/lang/Runnable;J)Ljava/util/concurrent/Future;
 	public fun submit (Ljava/lang/Runnable;)Ljava/util/concurrent/Future;

sentry/src/main/java/io/sentry/SentryExecutorService.java

@@ -149,17 +149,33 @@ public void prewarm() {
     }
   }
 
+  /**
+   * Whether the calling thread is one of the Sentry executor threads. Allocation-free replacement
+   * for scanning {@code Thread.currentThread().getName()}, which is on hot paths (e.g. scope
+   * persistence on every scope mutation).
+   */
+  public static boolean isSentryExecutorThread() {
+    return Thread.currentThread() instanceof SentryExecutorServiceThread;
+  }
+
   private static final class SentryExecutorServiceThreadFactory implements ThreadFactory {
     private int cnt;
 
     @Override
     public @NotNull Thread newThread(final @NotNull Runnable r) {
-      final Thread ret = new Thread(r, "SentryExecutorServiceThreadFactory-" + cnt++);
+      final Thread ret =
+          new SentryExecutorServiceThread(r, "SentryExecutorServiceThreadFactory-" + cnt++);
       ret.setDaemon(true);
       return ret;
     }
   }
 
+  private static final class SentryExecutorServiceThread extends Thread {
+    SentryExecutorServiceThread(final @NotNull Runnable r, final @NotNull String name) {
+      super(r, name);
+    }
+  }
+
   private static final class CancelledFuture<T> implements Future<T> {
     @Override
     public boolean cancel(final boolean mayInterruptIfRunning) {

sentry/src/main/java/io/sentry/cache/PersistingScopeObserver.java

@@ -7,6 +7,7 @@
 import io.sentry.Breadcrumb;
 import io.sentry.IScope;
 import io.sentry.ScopeObserverAdapter;
+import io.sentry.SentryExecutorService;
 import io.sentry.SentryLevel;
 import io.sentry.SentryOptions;
 import io.sentry.SpanContext;
@@ -229,7 +230,7 @@ private void serializeToDisk(final @NotNull Runnable task) {
     if (!options.isEnableScopePersistence()) {
       return;
     }
-    if (Thread.currentThread().getName().contains("SentryExecutor")) {
+    if (SentryExecutorService.isSentryExecutorThread()) {
       // we're already on the sentry executor thread, so we can just execute it directly
       try {
         task.run();