fix(analytics): resolve sessionId before assigning trackScreen state (v1.12.1+17)

The sessionId getter mints a fresh session on cold start or after a
30-min lapse, and as a side effect nulls _currentScreenName/_currentStepUid.
trackScreen() set those fields before calling the sessionId getter, so the
mint-on-cold-start side effect could immediately null the fields it had
just set, breaking the same-screen idempotency check and firing a
duplicate session_enter right after cold start.

Fix: resolve visitorId and sessionId into local variables before
assigning _currentScreenName/_currentStepUid, and use the locals in the
_enqueue() payload.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

lib/core/analytics/session_journey.dart

@@ -57,7 +57,13 @@
 /// `flutter_screen_views` row per screen; this is a Phase-1 backend gap,
 /// not a client bug, and applies identically here).
 ///
-/// Version: 1.0.0 | Created: 2026-09-25
+/// Version: 1.0.1 | Created: 2026-09-25 | Updated: 2026-09-25
+/// v1.0.1: trackScreen() resolved visitorId/sessionId into locals
+/// (resolvedVisitorId/resolvedSessionId) BEFORE assigning
+/// _currentScreenName/_currentStepUid, so the sessionId getter's
+/// mint-on-cold-start side effect (which nulls those fields) can no
+/// longer race the same-screen idempotency check and cause a duplicate
+/// session_enter right after cold start.
 library;
 
 import 'dart:async';
@@ -365,6 +371,17 @@ class SessionJourney extends WidgetsBindingObserver {
       return;
     }
     _leaveCurrentScreen();
+    // Resolve visitorId/sessionId BEFORE assigning _currentScreenName:
+    // sessionId's getter mints (and persists) a fresh session on a lapsed
+    // or cold window, and as a documented side effect of that mint it
+    // nulls _currentScreenName/_currentStepUid so the next trackScreen()
+    // re-enters cleanly under the new session. Reading it after already
+    // setting _currentScreenName below would immediately undo that
+    // assignment on every cold start, breaking this method's own
+    // same-screen idempotency and causing a duplicate session_enter on
+    // the very next call for the same screen. Found and fixed 2026-09-25.
+    final resolvedVisitorId = visitorId;
+    final resolvedSessionId = sessionId;
     final stepUid = newUuidV4();
     _currentScreenName = screenName;
     _currentStepUid = stepUid;
@@ -373,8 +390,8 @@ class SessionJourney extends WidgetsBindingObserver {
     _enqueue({
       'action': 'session_enter',
       'appKey': sessionJourneyAppKey,
-      'visitorId': visitorId,
-      'sessionId': sessionId,
+      'visitorId': resolvedVisitorId,
+      'sessionId': resolvedSessionId,
       'stepUid': stepUid,
       'platform': kIsWeb ? 'web' : 'unknown',
       'appVersion': appVersion,