// Intercept application submission request
if ($_SERVER['REQUEST_METHOD'] === 'POST' && isset($_POST['trigger_apply'])) {
    
    // 1. THE AUTHENTICATION GATEWAY
    if (!isset($_SESSION['employer_id'])) {
        // The user is an unauthenticated guest. 
        // We capture their exact current location so we can return them right back here later.
        $fallback_url = "employers/login.php?redirect=" . urlencode("job-details.php?id=" . $job_id);
        echo "<script>window.location.href='$fallback_url';</script>";
        exit;
    }
    
    // 2. THE DUPLICATE PROTECTION GUARD
    if (!$has_applied) {
        try {
            // Save application vector to the database tracking matrix
            $apply_stmt = $pdo->prepare("INSERT INTO applications (vacancy_id, employer_id, status) VALUES (?, ?, 'Submitted')");
            $apply_stmt->execute([$job_id, $_SESSION['employer_id']]);
            
            // Set state to true to instantly mutate the UI interface state
            $has_applied = true;
            $message = "<div class='alert alert-success fw-bold border-0 shadow-sm mb-4'><i class='fa-solid fa-circle-check me-2'></i>Application successfully sent! Your registered profile data and PDF CV have been routed directly to the recruiter's panel.</div>";
        } catch (\PDOException $e) {
            $message = "<div class='alert alert-danger border-0 shadow-sm mb-4'>Pipeline Error: " . $e->getMessage() . "</div>";
        }
    }
}