diff --git a/api/assign_ticket.php b/api/assign_ticket.php
index 351da55..0bd59d4 100644
--- a/api/assign_ticket.php
+++ b/api/assign_ticket.php
@@ -12,10 +12,10 @@ if (!is_array($data)) {
     exit;
 }
 
-$ticketId = isset($data['ticket_id']) ? (int)$data['ticket_id'] : null;
+$ticketId = isset($data['ticket_id']) ? (int)$data['ticket_id'] : 0;
 $assignedTo = $data['assigned_to'] ?? null;
 
-if (!$ticketId) {
+if ($ticketId <= 0) {
     http_response_code(400);
     echo json_encode(['success' => false, 'error' => 'Ticket ID required']);
     exit;
@@ -34,7 +34,7 @@ if (!$ticket || !$ticketModel->canUserAccessTicket($ticket, $currentUser)) {
 }
 
 // Authorization: only admins or the ticket creator/assignee can reassign
-if (!$isAdmin && $ticket['created_by'] !== $userId && $ticket['assigned_to'] !== $userId) {
+if (!$isAdmin && (int)$ticket['created_by'] !== (int)$userId && (int)$ticket['assigned_to'] !== (int)$userId) {
     http_response_code(403);
     echo json_encode(['success' => false, 'error' => 'Permission denied']);
     exit;
@@ -51,6 +51,7 @@ if ($assignedTo === null || $assignedTo === '') {
     $assignedTo = (int)$assignedTo;
     $targetUser = $userModel->getUserById($assignedTo);
     if (!$targetUser) {
+        http_response_code(400);
         echo json_encode(['success' => false, 'error' => 'Invalid user ID']);
         exit;
     }
diff --git a/api/export_tickets.php b/api/export_tickets.php
index 0e33b8e..68e19c7 100644
--- a/api/export_tickets.php
+++ b/api/export_tickets.php
@@ -21,7 +21,7 @@ try {
     require_once dirname(__DIR__) . '/models/TicketModel.php';
 
     // Check authentication via session
-    session_start();
+    if (session_status() === PHP_SESSION_NONE) { session_start(); }
     if (!isset($_SESSION['user']) || !isset($_SESSION['user']['user_id'])) {
         header('Content-Type: application/json');
         http_response_code(401);
diff --git a/assets/js/ticket.js b/assets/js/ticket.js
index efb6b27..81d4e3c 100644
--- a/assets/js/ticket.js
+++ b/assets/js/ticket.js
@@ -512,7 +512,7 @@ function renderDependencies(dependencies) {
                         <span class="dependency-title">${lt.escHtml(dep.title)}</span>
                         <span class="status-badge ${statusClass}">${lt.escHtml(dep.status)}</span>
                     </div>
-                    <button data-action="remove-dependency" data-dependency-id="${dep.dependency_id}" class="lt-btn lt-btn-sm">REMOVE</button>
+                    <button data-action="remove-dependency" data-dependency-id="${lt.escHtml(String(dep.dependency_id))}" class="lt-btn lt-btn-sm">REMOVE</button>
                 </div>`;
             });
 
diff --git a/models/CommentModel.php b/models/CommentModel.php
index b38e0ca..e0ae669 100644
--- a/models/CommentModel.php
+++ b/models/CommentModel.php
@@ -126,7 +126,7 @@ class CommentModel {
     private function buildCommentThread($comment, &$allComments) {
         $comment['replies'] = [];
         foreach ($allComments as $c) {
-            if ($c['parent_comment_id'] == $comment['comment_id']
+            if ((int)$c['parent_comment_id'] === (int)$comment['comment_id']
                 && isset($allComments[$c['comment_id']])) {
                 $comment['replies'][] = $this->buildCommentThread($c, $allComments);
             }
diff --git a/models/UserModel.php b/models/UserModel.php
index 0b34865..80a5bfb 100644
--- a/models/UserModel.php
+++ b/models/UserModel.php
@@ -227,7 +227,7 @@ class UserModel {
      * @return bool True if user is admin
      */
     public function isAdmin(array $user): bool {
-        return isset($user['is_admin']) && $user['is_admin'] == 1;
+        return isset($user['is_admin']) && (int)$user['is_admin'] === 1;
     }
 
     /**
diff --git a/views/TicketView.php b/views/TicketView.php
index a58d08e..c7a0d87 100644
--- a/views/TicketView.php
+++ b/views/TicketView.php
@@ -151,7 +151,7 @@ include __DIR__ . '/layout_header.php';
         <span class="lt-kv-value">
           <select id="prioritySelect" class="lt-select lt-select-sm editable-metadata" disabled aria-label="Priority">
             <?php foreach ([1=>'P1 - Critical',2=>'P2 - High',3=>'P3 - Medium',4=>'P4 - Low',5=>'P5 - Minimal'] as $v=>$l): ?>
-              <option value="<?= $v ?>" <?= $ticket['priority'] == $v ? 'selected' : '' ?>><?= $l ?></option>
+              <option value="<?= $v ?>" <?= (int)$ticket['priority'] === $v ? 'selected' : '' ?>><?= $l ?></option>
             <?php endforeach ?>
           </select>
         </span>
@@ -183,7 +183,7 @@ include __DIR__ . '/layout_header.php';
             <option value="">Unassigned</option>
             <?php foreach ($allUsers as $u): ?>
               <option value="<?= (int)$u['user_id'] ?>"
-                <?= ($ticket['assigned_to'] == $u['user_id']) ? 'selected' : '' ?>>
+                <?= ((int)$ticket['assigned_to'] === (int)$u['user_id']) ? 'selected' : '' ?>>
                 <?= htmlspecialchars($u['display_name'] ?? $u['username']) ?>
               </option>
             <?php endforeach ?>
@@ -361,7 +361,7 @@ include __DIR__ . '/layout_header.php';
           function renderComment(array $comment, ?int $currentUserId, bool $isAdmin, int $depth = 0): void {
               $displayName    = $comment['display_name_formatted'] ?? $comment['user_name'] ?? 'Unknown User';
               $commentId      = (int)$comment['comment_id'];
-              $isOwner        = ($comment['user_id'] == $currentUserId);
+              $isOwner        = ((int)$comment['user_id'] === (int)$currentUserId);
               $canModify      = $isOwner || $isAdmin;
               $markdownEnabled = (bool)($comment['markdown_enabled'] ?? false);
               $threadDepth    = (int)($comment['thread_depth'] ?? $depth);