fix(android-nav3): Ignore no-op nav transactions

Treat no-op transactions from scopes.startTransaction as 'not started' in BackStackObserver.

This prevents ignored or incompatible nav transactions from being bound to the default scope, which could otherwise leave a finished no-op transaction attached and block later real transactions until the next top-of-stack change.

Add a regression test proving the observer leaves scope.transaction unset when startTransaction returns NoOpTransaction.

Co-Authored-By: OpenAI GPT-5.4 <noreply@openai.com>

Author: 0xadam-brown

sentry-android-navigation3/src/main/kotlin/io/sentry/compose/navigation3/BackStackObserver.kt

@@ -326,6 +326,10 @@ private class NavTransaction(private val scopes: IScopes) {
         transactionOptions,
       )
 
+    if (transaction.isNoOp) {
+      return null
+    }
+
     activeNavTransaction = transaction
 
     transaction.apply {

sentry-android-navigation3/src/test/kotlin/io/sentry/compose/navigation3/BackStackObserverTest.kt

@@ -8,6 +8,7 @@ import io.sentry.IScope
 import io.sentry.IScopes
 import io.sentry.ISpan
 import io.sentry.ITransaction
+import io.sentry.NoOpTransaction
 import io.sentry.Scope
 import io.sentry.ScopeCallback
 import io.sentry.SentryOptions
@@ -574,6 +575,20 @@ class BackStackObserverTest {
     assertThat(fixture.scope.transaction).isSameInstanceAs(fixture.startedTransactions.single())
   }
 
+  @Test
+  fun `onBackStackChanged does not bind a no-op nav transaction to the scope`() {
+    val fixture = Fixture()
+    whenever(fixture.scopes.startTransaction(any<TransactionContext>(), any<TransactionOptions>()))
+      .thenReturn(NoOpTransaction.getInstance())
+    val sut = fixture.getSut(config = ObserverConfig(enableNavigationTransactions = true))
+
+    sut.onBackStackChanged(listOf(HomeRoute()))
+
+    assertThat(fixture.startedTransactions).isEmpty()
+    assertThat(fixture.scope.transaction).isNull()
+    assertThat(fixture.scope.screen).isEqualTo("/HomeRoute")
+  }
+
   @Test
   fun `onBackStackChanged clears tracked scope state when the back stack becomes empty`() {
     val fixture = Fixture()