fix(sample): Attribute initial Nav3 crashes correctly

Crash only after the first Checkout composition is applied so the navigation transaction and scenario tags are available for attribution. Apply the scenario tag directly to the scope transaction to keep history filtering robust.

Refs JAVA-274
Co-Authored-By: OpenAI Codex <noreply@openai.com>

Author: 0xadam-brown

sentry-samples/sentry-samples-android/src/main/java/io/sentry/samples/android/navigation/nav3/Nav3MultiActivity.kt

@@ -270,8 +270,8 @@ internal fun MultiActivityRoute(onOpenProducts: () -> Unit) {
  *   covered by another one.
  * @param onCompleteOrder Handles Checkout's "Complete Order" outside this root (e.g., by returning
  *   a result). When `null`, the confirmation is pushed onto this root's own back stack.
- * @param crashOnFirstComposition Crashes while composing the Checkout destination, i.e., while the
- *   root's first screen is being created, to check that the crash is attributed to that screen.
+ * @param crashOnFirstComposition Crashes when the Checkout destination's first composition is
+ *   applied, so its navigation transaction and tags can attribute the crash to that screen.
  */
 @OptIn(ExperimentalComposeUiApi::class)
 @Composable
@@ -417,12 +417,14 @@ internal fun MultiRootNavDisplay(
               }
             }
             entry<Nav3Route.Checkout> { route ->
-              if (crashOnFirstComposition) {
-                throw RuntimeException(
-                  "Fatal Nav3 ${scenario.label} crash during first composition"
-                )
-              }
               TracedNav3Route(route, scenario) {
+                if (crashOnFirstComposition) {
+                  SideEffect {
+                    throw RuntimeException(
+                      "Fatal Nav3 ${scenario.label} crash after first composition"
+                    )
+                  }
+                }
                 Nav3RouteWorkEffect(route, routeWorkOptions)
                 CheckoutRoute(
                   route = route,

sentry-samples/sentry-samples-android/src/main/java/io/sentry/samples/android/navigation/nav3/Nav3RouteScreens.kt

@@ -95,6 +95,7 @@ private fun tagCurrentNav3Scenario(scenario: Nav3Scenario, activityName: String)
   }
   Sentry.configureScope { scope ->
     scope.withTransaction { transaction ->
+      transaction?.setTag(NAV3_SCENARIO_TAG, scenario.label)
       transaction?.setTag(NAVIGATION_SAMPLE_ACTIVITY_TAG, activityName)
       transaction?.setTag(NAVIGATION_SAMPLE_SESSION_TAG, sessionId)
     }