refactor(extend-app-start): Return ExtendedAppStart from the listener instead of a callback

The listener now returns the created transaction+span (or null to decline)
rather than calling back into onExtended() while extendAppStart() holds the
lock. This removes the re-entrant lock acquisition and the A->B->A round trip,
collapsing two public methods into one linear flow.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: buenaflor

sentry-android-core/api/sentry-android-core.api

@@ -192,13 +192,18 @@ public final class io/sentry/android/core/AppStartExtension : io/sentry/IAppStar
 	public fun getExtendedAppStartSpan ()Lio/sentry/ISpan;
 	public fun getExtendedEndTime ()Lio/sentry/SentryDate;
 	public fun isActive ()Z
-	public fun onExtended (Lio/sentry/ITransaction;Lio/sentry/ISpan;)V
 	public fun reset ()V
 	public fun setExtendAppStartListener (Lio/sentry/android/core/AppStartExtension$ExtendAppStartListener;)V
 }
 
 public abstract interface class io/sentry/android/core/AppStartExtension$ExtendAppStartListener {
-	public abstract fun onExtendAppStartRequested ()V
+	public abstract fun onExtendAppStartRequested ()Lio/sentry/android/core/AppStartExtension$ExtendedAppStart;
+}
+
+public final class io/sentry/android/core/AppStartExtension$ExtendedAppStart {
+	public final field span Lio/sentry/ISpan;
+	public final field transaction Lio/sentry/ITransaction;
+	public fun <init> (Lio/sentry/ITransaction;Lio/sentry/ISpan;)V
 }
 
 public final class io/sentry/android/core/AppState : java/io/Closeable {

sentry-android-core/src/main/java/io/sentry/android/core/AppStartExtension.java

@@ -21,22 +21,36 @@
  * keeps the new "extend app start" concern out of that already-large class.
  *
  * <p>Both the eager standalone App Start {@link ITransaction} and its extended child {@link ISpan}
- * are created by the integration (which has access to scopes) and handed back here via {@link
- * #onExtended(ITransaction, ISpan)}. This component owns them from then on: it never stores them in
- * the integration's shared transaction field, so the per-activity cleanup can never cancel an
- * eagerly-created extension.
+ * are created by the integration (which has access to scopes) and returned to this component from
+ * {@link ExtendAppStartListener#onExtendAppStartRequested()}. This component owns them from then
+ * on: it never stores them in the integration's shared transaction field, so the per-activity
+ * cleanup can never cancel an eagerly-created extension.
  */
 @ApiStatus.Internal
 public final class AppStartExtension implements IAppStartExtender {
 
+  /**
+   * The standalone App Start transaction and its extended child span, created by the integration.
+   */
+  public static final class ExtendedAppStart {
+    public final @NotNull ITransaction transaction;
+    public final @NotNull ISpan span;
+
+    public ExtendedAppStart(final @NotNull ITransaction transaction, final @NotNull ISpan span) {
+      this.transaction = transaction;
+      this.span = span;
+    }
+  }
+
   /**
    * Notifies the integration that an extension was requested. The integration creates the
-   * standalone App Start transaction + extended child span (it has scopes) and hands them back via
-   * {@link #onExtended(ITransaction, ISpan)}. When no listener is registered (e.g. standalone
-   * tracing is disabled), {@link #extendAppStart()} is inert and the whole API stays a no-op.
+   * standalone App Start transaction + extended child span (it has scopes) and returns them, or
+   * returns {@code null} to decline (e.g. standalone tracing is disabled). When no listener is
+   * registered, {@link #extendAppStart()} is inert and the whole API stays a no-op.
    */
   public interface ExtendAppStartListener {
-    void onExtendAppStartRequested();
+    @Nullable
+    ExtendedAppStart onExtendAppStartRequested();
   }
 
   private final @NotNull AppStartMetrics metrics;
@@ -81,24 +95,15 @@ public void extendAppStart() {
       }
       final @Nullable ExtendAppStartListener listener = extendAppStartListener;
       if (listener != null) {
-        listener.onExtendAppStartRequested();
+        final @Nullable ExtendedAppStart extended = listener.onExtendAppStartRequested();
+        if (extended != null) {
+          this.extendedTransaction = extended.transaction;
+          this.extendedSpan = extended.span;
+        }
       }
     }
   }
 
-  /**
-   * Hands the eagerly-created standalone App Start transaction and its extended child span over to
-   * this component, which owns them from now on. Called synchronously by the integration while
-   * handling {@link ExtendAppStartListener#onExtendAppStartRequested()}.
-   */
-  public void onExtended(
-      final @NotNull ITransaction transaction, final @NotNull ISpan extendedSpan) {
-    try (final @NotNull ISentryLifecycleToken ignored = lock.acquire()) {
-      this.extendedTransaction = transaction;
-      this.extendedSpan = extendedSpan;
-    }
-  }
-
   @Override
   public void finishAppStart() {
     try (final @NotNull ISentryLifecycleToken ignored = lock.acquire()) {

sentry-android-core/src/test/java/io/sentry/android/core/AppStartExtensionTest.kt

@@ -39,15 +39,18 @@ class AppStartExtensionTest {
     txn: ITransaction = mock(),
     span: ISpan = mock(),
   ): Pair<ITransaction, ISpan> {
-    setExtendAppStartListener { onExtended(txn, span) }
+    setExtendAppStartListener { AppStartExtension.ExtendedAppStart(txn, span) }
     return txn to span
   }
 
   @Test
   fun `extendAppStart fires the listener when the window is open`() {
     val ext = extension(windowOpen = true)
     val calls = AtomicInteger()
-    ext.setExtendAppStartListener { calls.incrementAndGet() }
+    ext.setExtendAppStartListener {
+      calls.incrementAndGet()
+      null
+    }
     ext.extendAppStart()
     assertEquals(1, calls.get())
   }
@@ -56,7 +59,10 @@ class AppStartExtensionTest {
   fun `extendAppStart does not fire the listener when the window is closed`() {
     val ext = extension(windowOpen = false)
     val calls = AtomicInteger()
-    ext.setExtendAppStartListener { calls.incrementAndGet() }
+    ext.setExtendAppStartListener {
+      calls.incrementAndGet()
+      null
+    }
     ext.extendAppStart()
     assertEquals(0, calls.get())
   }
@@ -77,7 +83,7 @@ class AppStartExtensionTest {
     val span = mock<ISpan>()
     ext.setExtendAppStartListener {
       calls.incrementAndGet()
-      ext.onExtended(txn, span)
+      AppStartExtension.ExtendedAppStart(txn, span)
     }
     ext.extendAppStart()
     ext.extendAppStart()

sentry-android-core/src/test/java/io/sentry/android/core/performance/AppStartMetricsTest.kt

@@ -13,6 +13,7 @@ import io.sentry.DateUtils
 import io.sentry.IContinuousProfiler
 import io.sentry.ITransactionProfiler
 import io.sentry.SentryNanotimeDate
+import io.sentry.android.core.AppStartExtension
 import io.sentry.android.core.ContextUtils
 import io.sentry.android.core.CurrentActivityHolder
 import io.sentry.android.core.SentryAndroidOptions
@@ -1067,22 +1068,31 @@ class AppStartMetricsTest {
     assertSame(metrics.appStartExtension, metrics.appStartExtension)
   }
 
+  /** Drives the singleton's eager extension into the active state via the listener path. */
+  private fun activateExtension(metrics: AppStartMetrics) {
+    metrics.appStartExtension.setExtendAppStartListener {
+      AppStartExtension.ExtendedAppStart(mock(), mock())
+    }
+    metrics.appStartExtension.extendAppStart()
+    assertTrue(metrics.appStartExtension.isActive)
+  }
+
   @Test
   fun `clear resets the extension state`() {
     val metrics = AppStartMetrics.getInstance()
-    metrics.appStartExtension.onExtended(mock(), mock())
-    assertTrue(metrics.appStartExtension.isActive)
+    activateExtension(metrics)
     metrics.clear()
     assertFalse(metrics.appStartExtension.isActive)
+    metrics.appStartExtension.setExtendAppStartListener(null)
   }
 
   @Test
   fun `onAppStartSpansSent resets the extension state`() {
     val metrics = AppStartMetrics.getInstance()
-    metrics.appStartExtension.onExtended(mock(), mock())
-    assertTrue(metrics.appStartExtension.isActive)
+    activateExtension(metrics)
     metrics.onAppStartSpansSent()
     assertFalse(metrics.appStartExtension.isActive)
+    metrics.appStartExtension.setExtendAppStartListener(null)
   }
 
   // endregion