diff --git a/src/Entity/BookStackConfiguration.php b/src/Entity/BookStackConfiguration.php
index 48300fe..5bc546e 100644
--- a/src/Entity/BookStackConfiguration.php
+++ b/src/Entity/BookStackConfiguration.php
@@ -6,6 +6,7 @@ namespace App\Entity;
 
 use App\Repository\BookStackConfigurationRepository;
 use Doctrine\ORM\Mapping as ORM;
+use Symfony\Component\Validator\Constraints as Assert;
 
 #[ORM\Entity(repositoryClass: BookStackConfigurationRepository::class)]
 class BookStackConfiguration
@@ -16,6 +17,7 @@ class BookStackConfiguration
     private ?int $id = null;
 
     #[ORM\Column(length: 255, nullable: true)]
+    #[Assert\Url]
     private ?string $url = null;
 
     #[ORM\Column(type: 'text', nullable: true)]
diff --git a/src/Entity/ClientTicket.php b/src/Entity/ClientTicket.php
index e4daf47..54a4d7e 100644
--- a/src/Entity/ClientTicket.php
+++ b/src/Entity/ClientTicket.php
@@ -19,6 +19,7 @@ use Doctrine\Common\Collections\ArrayCollection;
 use Doctrine\Common\Collections\Collection;
 use Doctrine\ORM\Mapping as ORM;
 use Symfony\Component\Serializer\Attribute\Groups;
+use Symfony\Component\Validator\Constraints as Assert;
 
 #[ApiResource(
     operations: [
@@ -54,6 +55,27 @@ use Symfony\Component\Serializer\Attribute\Groups;
 )]
 class ClientTicket
 {
+    public const string TYPE_BUG         = 'bug';
+    public const string TYPE_IMPROVEMENT = 'improvement';
+    public const string TYPE_OTHER       = 'other';
+
+    public const array TYPES = [
+        self::TYPE_BUG,
+        self::TYPE_IMPROVEMENT,
+        self::TYPE_OTHER,
+    ];
+
+    public const string STATUS_NEW         = 'new';
+    public const string STATUS_IN_PROGRESS = 'in_progress';
+    public const string STATUS_DONE        = 'done';
+    public const string STATUS_REJECTED    = 'rejected';
+
+    public const array STATUSES = [
+        self::STATUS_NEW,
+        self::STATUS_IN_PROGRESS,
+        self::STATUS_DONE,
+        self::STATUS_REJECTED,
+    ];
     #[ORM\Id]
     #[ORM\GeneratedValue]
     #[ORM\Column]
@@ -66,6 +88,7 @@ class ClientTicket
 
     #[ORM\Column(length: 20)]
     #[Groups(['client_ticket:read', 'client_ticket:write', 'task:read'])]
+    #[Assert\Choice(choices: self::TYPES)]
     private ?string $type = null;
 
     #[ORM\Column(length: 255)]
@@ -78,10 +101,12 @@ class ClientTicket
 
     #[ORM\Column(length: 255, nullable: true)]
     #[Groups(['client_ticket:read', 'client_ticket:write'])]
+    #[Assert\Url]
     private ?string $url = null;
 
     #[ORM\Column(length: 20)]
     #[Groups(['client_ticket:read', 'client_ticket:write', 'task:read'])]
+    #[Assert\Choice(choices: self::STATUSES)]
     private ?string $status = 'new';
 
     #[ORM\Column(type: 'text', nullable: true)]
diff --git a/src/Entity/GiteaConfiguration.php b/src/Entity/GiteaConfiguration.php
index 0469ac5..45345ad 100644
--- a/src/Entity/GiteaConfiguration.php
+++ b/src/Entity/GiteaConfiguration.php
@@ -6,6 +6,7 @@ namespace App\Entity;
 
 use App\Repository\GiteaConfigurationRepository;
 use Doctrine\ORM\Mapping as ORM;
+use Symfony\Component\Validator\Constraints as Assert;
 
 #[ORM\Entity(repositoryClass: GiteaConfigurationRepository::class)]
 class GiteaConfiguration
@@ -16,6 +17,7 @@ class GiteaConfiguration
     private ?int $id = null;
 
     #[ORM\Column(length: 255, nullable: true)]
+    #[Assert\Url]
     private ?string $url = null;
 
     #[ORM\Column(type: 'text', nullable: true)]
diff --git a/src/Entity/TaskBookStackLink.php b/src/Entity/TaskBookStackLink.php
index 5bac0e5..34b3f01 100644
--- a/src/Entity/TaskBookStackLink.php
+++ b/src/Entity/TaskBookStackLink.php
@@ -7,6 +7,7 @@ namespace App\Entity;
 use App\Repository\TaskBookStackLinkRepository;
 use DateTimeImmutable;
 use Doctrine\ORM\Mapping as ORM;
+use Symfony\Component\Validator\Constraints as Assert;
 
 #[ORM\Entity(repositoryClass: TaskBookStackLinkRepository::class)]
 #[ORM\UniqueConstraint(name: 'UNIQ_task_bookstack_link', columns: ['task_id', 'bookstack_id', 'bookstack_type'])]
@@ -31,6 +32,7 @@ class TaskBookStackLink
     private string $title;
 
     #[ORM\Column(length: 500)]
+    #[Assert\Url]
     private string $url;
 
     #[ORM\Column]
diff --git a/src/Repository/ClientTicketRepository.php b/src/Repository/ClientTicketRepository.php
index 37815b0..9ca3726 100644
--- a/src/Repository/ClientTicketRepository.php
+++ b/src/Repository/ClientTicketRepository.php
@@ -20,18 +20,26 @@ class ClientTicketRepository extends ServiceEntityRepository
     }
 
     /**
-     * Returns the next ticket number for a project, using a row-level lock
+     * Returns the max ticket number for a project, using an advisory lock
      * to prevent race conditions when creating tickets concurrently.
      */
-    public function findNextNumberForProjectForUpdate(Project $project): int
+    public function findMaxNumberByProjectForUpdate(Project $project): int
     {
         $conn = $this->getEntityManager()->getConnection();
 
+        // Use PostgreSQL advisory lock instead of FOR UPDATE
+        // because FOR UPDATE is not allowed with aggregate functions in PostgreSQL.
+        // Offset by 1000000 to avoid collision with task locks on the same project ID.
+        $conn->executeStatement(
+            'SELECT pg_advisory_xact_lock(:lockKey)',
+            ['lockKey' => $project->getId() + 1000000],
+        );
+
         $result = $conn->fetchOne(
-            'SELECT COALESCE(MAX(number), 0) FROM client_ticket WHERE project_id = :project FOR UPDATE',
+            'SELECT COALESCE(MAX(number), 0) FROM client_ticket WHERE project_id = :project',
             ['project' => $project->getId()],
         );
 
-        return ((int) $result) + 1;
+        return (int) $result;
     }
 }
diff --git a/src/Repository/TaskRepository.php b/src/Repository/TaskRepository.php
index 99857a5..5922bcc 100644
--- a/src/Repository/TaskRepository.php
+++ b/src/Repository/TaskRepository.php
@@ -20,13 +20,20 @@ class TaskRepository extends ServiceEntityRepository
     }
 
     /**
-     * Returns the max task number for a project, using a row-level lock
+     * Returns the max task number for a project, using an advisory lock
      * to prevent race conditions when creating tasks concurrently.
      */
     public function findMaxNumberByProjectForUpdate(Project $project): int
     {
         $conn = $this->getEntityManager()->getConnection();
 
+        // Use PostgreSQL advisory lock (project ID as lock key) instead of FOR UPDATE
+        // because FOR UPDATE is not allowed with aggregate functions in PostgreSQL.
+        $conn->executeStatement(
+            'SELECT pg_advisory_xact_lock(:project)',
+            ['project' => $project->getId()],
+        );
+
         $result = $conn->fetchOne(
             'SELECT COALESCE(MAX(number), 0) FROM task WHERE project_id = :project',
             ['project' => $project->getId()],
diff --git a/src/State/ClientTicketNumberProcessor.php b/src/State/ClientTicketNumberProcessor.php
index f96e4ba..49bebcc 100644
--- a/src/State/ClientTicketNumberProcessor.php
+++ b/src/State/ClientTicketNumberProcessor.php
@@ -53,7 +53,8 @@ final readonly class ClientTicketNumberProcessor implements ProcessorInterface
 
         $now = new DateTimeImmutable();
 
-        $data->setNumber($this->clientTicketRepository->findNextNumberForProjectForUpdate($project));
+        $maxNumber = $this->clientTicketRepository->findMaxNumberByProjectForUpdate($project);
+        $data->setNumber($maxNumber + 1);
         $data->setSubmittedBy($user);
         $data->setStatus('new');
         $data->setCreatedAt($now);