diff --git a/phpstan.neon b/phpstan.neon
index 64e5e97c..93f52b64 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -1,5 +1,5 @@
 parameters:
-    level: 2
+    level: 3
     paths:
         - src/
         - tests/
diff --git a/src/Application/CommandBus.php b/src/Application/CommandBus.php
index 354c7488..cdc3eef8 100644
--- a/src/Application/CommandBus.php
+++ b/src/Application/CommandBus.php
@@ -14,7 +14,7 @@
 namespace Streak\Application;
 
 use Streak\Domain;
-use Streak\Domain\Exception\CommandNotSupported;
+use Streak\Domain\Exception;
 
 /**
  * @author Alan Gabriel Bem <alan.bem@gmail.com>
@@ -22,7 +22,8 @@
 interface CommandBus
 {
     /**
-     * @throws CommandNotSupported
+     * @throws Exception\CommandNotSupported
+     * @throws Exception\ConcurrentWriteDetected
      */
     public function dispatch(Domain\Command $command): void;
 }
diff --git a/src/Domain/AggregateRoot/EventSourcing.php b/src/Domain/AggregateRoot/EventSourcing.php
index 139a985a..7171e8c6 100644
--- a/src/Domain/AggregateRoot/EventSourcing.php
+++ b/src/Domain/AggregateRoot/EventSourcing.php
@@ -101,7 +101,6 @@ final public function applyEvent(Event\Envelope $event): void
         }
 
         foreach ($this->eventSourcedEntities() as $entity) {
-            /** @var Event\Sourced\Entity $entity */
             if ($entity->id()->equals($event->entityId())) {
                 $aggregate = $entity;
                 $stack = [];
@@ -147,9 +146,9 @@ private function apply(Event $event): void
     }
 
     /**
-     * @return Event\Sourced\Entity[]
+     * @return \Generator<Event\Sourced\Entity>
      */
-    private function eventSourcedEntities(): iterable
+    private function eventSourcedEntities(): \Generator
     {
         yield from Event\Sourced\Entity\Helper::for($this)->extractEventSourcedEntities();
     }
diff --git a/src/Domain/Envelope.php b/src/Domain/Envelope.php
index 382b79cb..5e6bec7a 100644
--- a/src/Domain/Envelope.php
+++ b/src/Domain/Envelope.php
@@ -16,6 +16,8 @@
 use Streak\Domain\Id\UUID;
 
 /**
+ * @template T of object
+ *
  * @author Alan Gabriel Bem <alan.bem@gmail.com>
  */
 interface Envelope extends ValueObject
@@ -24,12 +26,15 @@ public function uuid(): UUID;
 
     public function name(): string;
 
+    /**
+     * @return T
+     */
     public function message();
 
     /**
      * @param string $name
      *
-     * @return float|int|string|null
+     * @return null|scalar
      */
     public function get($name);
 
diff --git a/src/Domain/Event/Converter.php b/src/Domain/Event/Converter.php
index 52ccba95..c9f9e751 100644
--- a/src/Domain/Event/Converter.php
+++ b/src/Domain/Event/Converter.php
@@ -20,11 +20,13 @@ interface Converter
 {
     /**
      * @throws Exception\ConversionToArrayNotPossible
+     * @throws \Exception
      */
     public function objectToArray(object $object): array;
 
     /**
      * @throws Exception\ConversionToObjectNotPossible
+     * @throws \Exception
      */
     public function arrayToObject(array $data): object;
 }
diff --git a/src/Domain/Event/Envelope.php b/src/Domain/Event/Envelope.php
index 47ac1484..cb6e1471 100644
--- a/src/Domain/Event/Envelope.php
+++ b/src/Domain/Event/Envelope.php
@@ -20,7 +20,8 @@
 /**
  * @author Alan Gabriel Bem <alan.bem@gmail.com>
  *
- * @template T of Event
+ * @template TMessage as Event
+ * @implements Domain\Envelope<TMessage>
  *
  * @see \Streak\Domain\Event\EnvelopeTest
  */
@@ -33,26 +34,45 @@ final class Envelope implements Domain\Envelope
     public const METADATA_PRODUCER_ID = 'producer_id';
     public const METADATA_ENTITY_TYPE = 'entity_type';
     public const METADATA_ENTITY_ID = 'entity_id';
-    private array $metadata = [];
 
     /**
-     * @param T $message
+     * @var-phpstan non-empty-array<non-empty-string, scalar>
+     * @var-psalm non-empty-array<non-empty-string, scalar>&array{
+     *          uuid: non-empty-string,
+     *          name: non-empty-string,
+     *          producer_type: class-string<Domain\Id>,
+     *          producer_id: non-empty-string,
+     *          entity_type: class-string<Domain\Id>,
+     *          entity_id: non-empty-string,
+     *          version?: positive-int,
+     * }
+     */
+    private array $metadata;
+
+    /**
+     * @param non-empty-string $name
+     * @param TMessage $message
      */
     public function __construct(UUID $uuid, string $name, private Event $message, Domain\Id $producerId, Domain\Id $entityId, ?int $version = null)
     {
-        $this->metadata[self::METADATA_UUID] = $uuid->toString();
-        $this->metadata[self::METADATA_NAME] = $name;
-        $this->metadata[self::METADATA_PRODUCER_TYPE] = $producerId::class;
-        $this->metadata[self::METADATA_PRODUCER_ID] = $producerId->toString();
-        $this->metadata[self::METADATA_ENTITY_TYPE] = $entityId::class;
-        $this->metadata[self::METADATA_ENTITY_ID] = $entityId->toString();
+        $this->metadata = [
+            self::METADATA_UUID => $uuid->toString(),
+            self::METADATA_NAME => $name,
+            self::METADATA_PRODUCER_TYPE => $producerId::class,
+            self::METADATA_PRODUCER_ID => $producerId->toString(),
+            self::METADATA_ENTITY_TYPE => $entityId::class,
+            self::METADATA_ENTITY_ID => $entityId->toString(),
+        ];
         if (null !== $version) {
             $this->metadata[self::METADATA_VERSION] = $version;
         }
     }
 
     /**
-     * @return Envelope<T>
+     * @template TEvent of Event
+     * @param TEvent $message
+     *
+     * @return self<TEvent>
      */
     public static function new(Event $message, Domain\Id $producerId, ?int $version = null): self
     {
@@ -61,55 +81,54 @@ public static function new(Event $message, Domain\Id $producerId, ?int $version
 
     public function uuid(): UUID
     {
-        return new UUID($this->get(self::METADATA_UUID));
+        return new UUID($this->metadata[self::METADATA_UUID]);
     }
 
+    /**
+     * @return non-empty-string
+     */
     public function name(): string
     {
-        return $this->get(self::METADATA_NAME);
+        return $this->metadata[self::METADATA_NAME];
     }
 
-    /**
-     * @return T
-     */
-    public function message(): Event
+    public function message()
     {
         return $this->message;
     }
 
     public function producerId(): Domain\Id
     {
-        $class = $this->get(self::METADATA_PRODUCER_TYPE);
+        $class = $this->metadata[self::METADATA_PRODUCER_TYPE];
+        $id = $this->metadata[self::METADATA_PRODUCER_ID];
 
         /** @var class-string<Domain\Id> $class */
-        /** @phpstan-var class-string<Domain\Id> $class */
-        /** @psalm-var class-string<Domain\Id> $class */
-        return $class::fromString($this->get(self::METADATA_PRODUCER_ID));
+        return $class::fromString($id);
     }
 
     public function entityId(): Domain\Id
     {
-        $class = $this->get(self::METADATA_ENTITY_TYPE);
+        $class = $this->metadata[self::METADATA_ENTITY_TYPE];
+        $id = $this->metadata[self::METADATA_ENTITY_ID];
 
         /** @var class-string<Domain\Id> $class */
-        /** @phpstan-var class-string<Domain\Id> $class */
-        /** @psalm-var class-string<Domain\Id> $class */
-        return $class::fromString($this->get(self::METADATA_ENTITY_ID));
+        return $class::fromString($id);
     }
 
     public function version(): ?int
     {
-        return $this->get(self::METADATA_VERSION);
+        return $this->metadata[self::METADATA_VERSION] ?? null;
     }
 
-    public function set(string $name, $value): self
+    /**
+     * @param non-empty-string $name
+     * @return self<TMessage>
+     */
+    public function set(string $name, bool|float|int|string $value): self
     {
-        if (empty($name)) {
+        if (empty($name)) { // @phpstan-ignore-line
             throw new \InvalidArgumentException('Name of the attribute can not be empty.');
         }
-        if (!\is_scalar($value)) {
-            throw new \InvalidArgumentException(sprintf('Value for attribute "%s" is a scalar.', $name));
-        }
 
         $new = new self(
             $this->uuid(),
@@ -149,6 +168,9 @@ public function equals(object $envelope): bool
         return true;
     }
 
+    /**
+     * @return self<TMessage>
+     */
     public function defineVersion(int $version): self
     {
         return new self(
@@ -161,6 +183,9 @@ public function defineVersion(int $version): self
         );
     }
 
+    /**
+     * @return self<TMessage>
+     */
     public function defineEntityId(Domain\Id $entityId): self
     {
         return new self(
diff --git a/src/Domain/Event/Exception/SourcingObjectWithEventFailed.php b/src/Domain/Event/Exception/SourcingObjectWithEventFailed.php
index e5a948b0..a3df9899 100644
--- a/src/Domain/Event/Exception/SourcingObjectWithEventFailed.php
+++ b/src/Domain/Event/Exception/SourcingObjectWithEventFailed.php
@@ -29,7 +29,7 @@ public function __construct(private object $subject, private Event\Envelope $eve
         parent::__construct($message, 0, $previous);
     }
 
-    public function subject()
+    public function subject(): object
     {
         return $this->subject;
     }
diff --git a/src/Domain/Event/Listener/Factory.php b/src/Domain/Event/Listener/Factory.php
index 1ca6760d..6a42573d 100644
--- a/src/Domain/Event/Listener/Factory.php
+++ b/src/Domain/Event/Listener/Factory.php
@@ -15,20 +15,25 @@
 
 use Streak\Domain\Event;
 use Streak\Domain\Event\Exception\InvalidEventGiven;
-use Streak\Domain\Event\Listener;
 use Streak\Domain\Exception\InvalidIdGiven;
 
 /**
+ * @template T of Event\Listener
+ *
  * @author Alan Gabriel Bem <alan.bem@gmail.com>
  */
 interface Factory
 {
     /**
+     * @return T
+     *
      * @throws InvalidIdGiven
      */
-    public function create(Listener\Id $id): Listener;
+    public function create(Event\Listener\Id $id): Event\Listener;
 
     /**
+     * @return T
+     *
      * @throws InvalidEventGiven
      */
     public function createFor(Event\Envelope $event): Event\Listener;
diff --git a/src/Domain/Event/Metadata.php b/src/Domain/Event/Metadata.php
index b10c7b4d..6e272bbf 100644
--- a/src/Domain/Event/Metadata.php
+++ b/src/Domain/Event/Metadata.php
@@ -20,6 +20,9 @@
  */
 final class Metadata
 {
+    /**
+     * @var array<string, string>
+     */
     private array $metadata = [];
 
     private function __construct(array $metadata)
@@ -34,7 +37,7 @@ public function set(string $name, string $value): void
         $this->metadata[$name] = $value;
     }
 
-    public function has(string $name)
+    public function has(string $name): bool
     {
         if (isset($this->metadata[$name])) {
             return true;
@@ -52,7 +55,7 @@ public function get(string $name, string $default = null): ?string
         return $this->metadata[$name];
     }
 
-    public static function fromObject($object): self
+    public static function fromObject(object $object): self
     {
         if (!isset($object->__streak_metadata)) {
             return new self([]);
@@ -77,7 +80,7 @@ public static function fromArray(array $metadata): self
         return new self($metadata);
     }
 
-    public function toObject($object): void
+    public function toObject(object $object): void
     {
         $object->__streak_metadata = $this->metadata;
     }
diff --git a/src/Domain/Event/Sourced/Entity/Helper.php b/src/Domain/Event/Sourced/Entity/Helper.php
index 61e2efcf..76514cb8 100644
--- a/src/Domain/Event/Sourced/Entity/Helper.php
+++ b/src/Domain/Event/Sourced/Entity/Helper.php
@@ -42,9 +42,9 @@ public function applyEvent(Event\Envelope $event): void
     }
 
     /**
-     * @return Event\Sourced\Entity[]
+     * @return \Generator<int, Event\Sourced\Entity>
      */
-    public function extractEventSourcedEntities(): iterable
+    public function extractEventSourcedEntities(): \Generator
     {
         yield from self::doExtractEventSourcedEntities($this->object);
     }
@@ -128,8 +128,10 @@ private static function applyEventByArgumentType(Event\Envelope $event, object &
 
     /**
      * Extract event sourced entities recursively.
+     *
+     * @return \Generator<int, Event\Sourced\Entity>
      */
-    private static function doExtractEventSourcedEntities(object $object, array &$ignored = []): iterable
+    private static function doExtractEventSourcedEntities(object $object, array &$ignored = []): \Generator
     {
         $ignored[] = $object;
 
diff --git a/src/Domain/Event/Subscription/Factory.php b/src/Domain/Event/Subscription/Factory.php
index b5ddf677..40d3a030 100644
--- a/src/Domain/Event/Subscription/Factory.php
+++ b/src/Domain/Event/Subscription/Factory.php
@@ -16,9 +16,14 @@
 use Streak\Domain\Event;
 
 /**
+ * @template T of Event\Subscription
+ *
  * @author Alan Gabriel Bem <alan.bem@gmail.com>
  */
 interface Factory
 {
+    /**
+     * @return T
+     */
     public function create(Event\Listener $listener): Event\Subscription;
 }
diff --git a/src/Domain/Id.php b/src/Domain/Id.php
index a68b7ec6..6ff97d06 100644
--- a/src/Domain/Id.php
+++ b/src/Domain/Id.php
@@ -20,7 +20,13 @@
  */
 interface Id extends Domain\ValueObject
 {
+    /**
+     * @return non-empty-string
+     */
     public function toString(): string;
 
-    public static function fromString(string $id): Domain\Id;
+    /**
+     * @param non-empty-string $id
+     */
+    public static function fromString(string $id): static;
 }
diff --git a/src/Domain/Id/UUID.php b/src/Domain/Id/UUID.php
index fbd16182..ac00e000 100644
--- a/src/Domain/Id/UUID.php
+++ b/src/Domain/Id/UUID.php
@@ -25,8 +25,12 @@
  */
 class UUID implements Domain\Id
 {
+    /** @var non-empty-string */
     private string $value;
 
+    /**
+     * @param non-empty-string $value
+     */
     final public function __construct(string $value)
     {
         $value = mb_strtolower($value);
@@ -44,10 +48,10 @@ final public function __construct(string $value)
             throw new \InvalidArgumentException();
         }
 
-        $this->value = $value;
+        $this->value = $value; // @phpstan-ignore-line
     }
 
-    public static function random()
+    public static function random(): static
     {
         $uuid = \Ramsey\Uuid\Uuid::uuid4()->toString();
 
@@ -72,10 +76,7 @@ public function toString(): string
         return $this->value;
     }
 
-    /**
-     * @return static
-     */
-    public static function fromString(string $id): Domain\Id
+    public static function fromString(string $id): static
     {
         return new static($id);
     }
diff --git a/src/Infrastructure/Application/Sensor/CommittingSensor/Factory.php b/src/Infrastructure/Application/Sensor/CommittingSensor/Factory.php
index 78c114cc..38721aeb 100644
--- a/src/Infrastructure/Application/Sensor/CommittingSensor/Factory.php
+++ b/src/Infrastructure/Application/Sensor/CommittingSensor/Factory.php
@@ -28,7 +28,7 @@ public function __construct(private Sensor\Factory $factory, private UnitOfWork
     {
     }
 
-    public function create(): Sensor
+    public function create(): CommittingSensor
     {
         $sensor = $this->factory->create();
 
diff --git a/src/Infrastructure/Domain/AggregateRoot/Snapshotter/Storage/RedisStorage.php b/src/Infrastructure/Domain/AggregateRoot/Snapshotter/Storage/RedisStorage.php
index af3316d1..9055aa3c 100644
--- a/src/Infrastructure/Domain/AggregateRoot/Snapshotter/Storage/RedisStorage.php
+++ b/src/Infrastructure/Domain/AggregateRoot/Snapshotter/Storage/RedisStorage.php
@@ -20,6 +20,8 @@
 
 /**
  * @author Alan Gabriel Bem <alan.bem@gmail.com>
+ *
+ * @see \Streak\Infrastructure\Domain\AggregateRoot\Snapshotter\Storage\RedisStorageTest
  */
 final class RedisStorage implements Storage, Resettable
 {
@@ -38,12 +40,17 @@ public function find(AggregateRoot $aggregate): string
             throw new SnapshotNotFound($aggregate);
         }
 
+        // Redis::get() can return Redis instance when it's in multi() mode.
+        if ($snapshot instanceof \Redis) {
+            throw new SnapshotNotFound($aggregate);
+        }
+
         return $snapshot;
     }
 
     public function store(AggregateRoot $aggregate, string $snapshot): void
     {
-        $this->redis->set($this->key($aggregate), (string) $snapshot);
+        $this->redis->set($this->key($aggregate), $snapshot);
     }
 
     public function reset(): bool
diff --git a/src/Infrastructure/Domain/Event/Converter/CompositeConverter.php b/src/Infrastructure/Domain/Event/Converter/CompositeConverter.php
index bbf8f50a..9555fcbc 100644
--- a/src/Infrastructure/Domain/Event/Converter/CompositeConverter.php
+++ b/src/Infrastructure/Domain/Event/Converter/CompositeConverter.php
@@ -38,9 +38,6 @@ public function addConverter(Converter $converter): void
         $this->converters[] = $converter;
     }
 
-    /**
-     * @throws Exception\ConversionToArrayNotPossible
-     */
     public function objectToArray(object $object): array
     {
         foreach ($this->converters as $converter) {
@@ -56,9 +53,6 @@ public function objectToArray(object $object): array
         throw new Exception\ConversionToArrayNotPossible($object);
     }
 
-    /**
-     * @throws Exception\ConversionToObjectNotPossible
-     */
     public function arrayToObject(array $data): object
     {
         $previous = null;
diff --git a/src/Infrastructure/Domain/Event/LoggingListener/Factory.php b/src/Infrastructure/Domain/Event/LoggingListener/Factory.php
index 761a368d..798e628c 100644
--- a/src/Infrastructure/Domain/Event/LoggingListener/Factory.php
+++ b/src/Infrastructure/Domain/Event/LoggingListener/Factory.php
@@ -18,6 +18,8 @@
 use Streak\Infrastructure\Domain\Event\LoggingListener;
 
 /**
+ * @implements Event\Listener\Factory<LoggingListener>
+ *
  * @author Alan Gabriel Bem <alan.bem@gmail.com>
  *
  * @see \Streak\Infrastructure\Domain\Event\LoggingListener\FactoryTest
@@ -28,14 +30,14 @@ public function __construct(private Event\Listener\Factory $factory, private Log
     {
     }
 
-    public function create(Event\Listener\Id $id): Event\Listener
+    public function create(Event\Listener\Id $id): LoggingListener
     {
         $saga = $this->factory->create($id);
 
         return new LoggingListener($saga, $this->logger);
     }
 
-    public function createFor(Event\Envelope $event): Event\Listener
+    public function createFor(Event\Envelope $event): LoggingListener
     {
         $listener = $this->factory->createFor($event);
 
diff --git a/src/Infrastructure/Domain/Event/NullListener.php b/src/Infrastructure/Domain/Event/NullListener.php
index 26fa4569..ebd12a25 100644
--- a/src/Infrastructure/Domain/Event/NullListener.php
+++ b/src/Infrastructure/Domain/Event/NullListener.php
@@ -30,7 +30,7 @@ public function on(Event\Envelope $event): bool
         return true;
     }
 
-    public static function from(Event\Listener $listener)
+    public static function from(Event\Listener $listener): self
     {
         return new self($listener->id());
     }
diff --git a/src/Infrastructure/Domain/Event/Sourced/Subscription/InMemoryState.php b/src/Infrastructure/Domain/Event/Sourced/Subscription/InMemoryState.php
index 3364262a..72b6d265 100644
--- a/src/Infrastructure/Domain/Event/Sourced/Subscription/InMemoryState.php
+++ b/src/Infrastructure/Domain/Event/Sourced/Subscription/InMemoryState.php
@@ -22,6 +22,9 @@
  */
 class InMemoryState implements State
 {
+    /**
+     * @var array<string, scalar>
+     */
     private array $state = [];
 
     private function __construct()
@@ -55,7 +58,10 @@ public function get(string $name)
         return $this->state[$name];
     }
 
-    public function set(string $name, $value): State
+    /**
+     * @param array|scalar|null $value
+     */
+    public function set(string $name, $value): self
     {
         $this->validate($name, $value);
 
@@ -94,6 +100,9 @@ public static function empty(): self
         return new self();
     }
 
+    /**
+     * @param array|scalar|null $value
+     */
     private function validate(string $name, $value): void
     {
         if (true === empty($name)) {
diff --git a/src/Infrastructure/Domain/Event/Subscription/CommittingSubscription/Factory.php b/src/Infrastructure/Domain/Event/Subscription/CommittingSubscription/Factory.php
index b46bfc3f..3eb9460c 100644
--- a/src/Infrastructure/Domain/Event/Subscription/CommittingSubscription/Factory.php
+++ b/src/Infrastructure/Domain/Event/Subscription/CommittingSubscription/Factory.php
@@ -19,6 +19,8 @@
 use Streak\Infrastructure\Domain\UnitOfWork;
 
 /**
+ * @implements Event\Subscription\Factory<CommittingSubscription>
+ *
  * @author Alan Gabriel Bem <alan.bem@gmail.com>
  *
  * @see \Streak\Infrastructure\Domain\Event\Subscription\CommittingSubscription\FactoryTest
@@ -29,7 +31,7 @@ public function __construct(private Subscription\Factory $factory, private UnitO
     {
     }
 
-    public function create(Event\Listener $listener): Event\Subscription
+    public function create(Event\Listener $listener): CommittingSubscription
     {
         $subscription = $this->factory->create($listener);
 
diff --git a/src/Infrastructure/Domain/Event/Subscription/DAO.php b/src/Infrastructure/Domain/Event/Subscription/DAO.php
index 8087dcc0..465ae458 100644
--- a/src/Infrastructure/Domain/Event/Subscription/DAO.php
+++ b/src/Infrastructure/Domain/Event/Subscription/DAO.php
@@ -30,7 +30,7 @@ public function exists(Listener\Id $id): bool;
     /**
      * @param string[] $types
      *
-     * @return DAO\Subscription[]
+     * @return iterable<int,Subscription>
      */
     public function all(array $types = [], ?bool $completed = null): iterable;
 }
diff --git a/src/Infrastructure/Domain/Event/Subscription/DAO/DbalPostgresDAO.php b/src/Infrastructure/Domain/Event/Subscription/DAO/DbalPostgresDAO.php
index 409ebb42..47874063 100644
--- a/src/Infrastructure/Domain/Event/Subscription/DAO/DbalPostgresDAO.php
+++ b/src/Infrastructure/Domain/Event/Subscription/DAO/DbalPostgresDAO.php
@@ -30,8 +30,13 @@
  */
 class DbalPostgresDAO implements DAO
 {
-    public function __construct(private Subscription\Factory $subscriptions, private Event\Listener\Factory $listeners, private Connection $connection, private Event\Converter $converter)
-    {
+    public function __construct(
+        /** @var Subscription\Factory<DAO\Subscription> */
+        private Subscription\Factory $subscriptions,
+        private Event\Listener\Factory $listeners,
+        private Connection $connection,
+        private Event\Converter $converter
+    ) {
     }
 
     /**
@@ -69,11 +74,9 @@ public function exists(Listener\Id $id): bool
     }
 
     /**
-     * @param string[] $types
+     * @return \Generator<int, Subscription>
      *
      * @throws \Doctrine\DBAL\DBALException
-     *
-     * @return Subscription[]
      */
     public function all(array $types = [], ?bool $completed = null): iterable
     {
@@ -186,7 +189,7 @@ public function drop(): void
         $statement->execute();
     }
 
-    private function fromRow($row): Subscription
+    private function fromRow($row): DAO\Subscription
     {
         $id = $row['subscription_type'];
         $id = $id::fromString($row['subscription_id']);
@@ -306,11 +309,9 @@ private function doSave(DAO\Subscription $subscription): void
     }
 
     /**
-     *
      * @throws \Doctrine\DBAL\DBALException
-     * @return \Streak\Infrastructure\Domain\Event\Subscription\DAO\Subscription|null
      */
-    private function doOne(Event\Listener\Id $id)
+    private function doOne(Event\Listener\Id $id): ?DAO\Subscription
     {
         $sql = 'SELECT subscription_type, subscription_id, subscription_version, state, started_by, started_at, last_processed_event, last_event_processed_at, completed, paused_at FROM subscriptions WHERE subscription_type = :subscription_type AND subscription_id = :subscription_id LIMIT 1';
 
@@ -354,6 +355,8 @@ private function doExists(Listener\Id $id): bool
     }
 
     /**
+     * @return \Generator<int, Subscription>
+     *
      * @throws \Doctrine\DBAL\DBALException
      */
     private function doAll(array $types, ?bool $completed): \Generator
diff --git a/src/Infrastructure/Domain/Event/Subscription/DAO/InMemoryDAO.php b/src/Infrastructure/Domain/Event/Subscription/DAO/InMemoryDAO.php
index 56360950..cac5f52f 100644
--- a/src/Infrastructure/Domain/Event/Subscription/DAO/InMemoryDAO.php
+++ b/src/Infrastructure/Domain/Event/Subscription/DAO/InMemoryDAO.php
@@ -60,7 +60,7 @@ public function exists(Listener\Id $id): bool
 
     public function all(array $types = [], ?bool $completed = null): iterable
     {
-        foreach ($this->subscriptions as $key => $stored) {
+        foreach ($this->subscriptions as $stored) {
             if (\count($types)) {
                 $type = $stored->id()::class;
                 if (false === \in_array($type, $types)) {
diff --git a/src/Infrastructure/Domain/Event/Subscription/DAO/Subscription.php b/src/Infrastructure/Domain/Event/Subscription/DAO/Subscription.php
index 3c09522f..29b2e418 100644
--- a/src/Infrastructure/Domain/Event/Subscription/DAO/Subscription.php
+++ b/src/Infrastructure/Domain/Event/Subscription/DAO/Subscription.php
@@ -16,6 +16,7 @@
 use Streak\Domain\Clock;
 use Streak\Domain\Event;
 use Streak\Domain\Event\Listener;
+use Streak\Domain\Event\Listener\State;
 use Streak\Domain\Event\Subscription\Exception;
 use Streak\Domain\EventStore;
 use Streak\Infrastructure\Domain\Event\Sourced\Subscription\InMemoryState;
@@ -28,12 +29,12 @@
 class Subscription implements Event\Subscription
 {
     private const LIMIT_TO_INITIAL_STREAM = 0;
-    private InMemoryState $state;
+    private State $state;
     private ?Event\Envelope $startedBy = null;
-    private ?\DateTimeImmutable $startedAt = null;
+    private ?\DateTimeImmutable $startedAt = null; // @TODO: check if needed
     private ?\DateTimeImmutable $pausedAt = null;
     private ?Event\Envelope $lastProcessedEvent = null;
-    private ?\DateTimeImmutable $lastEventProcessedAt = null;
+    private ?\DateTimeImmutable $lastEventProcessedAt = null; // @TODO: check if needed
     private int $version = 0;
     private bool $completed = false;
 
diff --git a/src/Infrastructure/Domain/Event/Subscription/DAO/Subscription/Factory.php b/src/Infrastructure/Domain/Event/Subscription/DAO/Subscription/Factory.php
index 3568288c..ccfc119e 100644
--- a/src/Infrastructure/Domain/Event/Subscription/DAO/Subscription/Factory.php
+++ b/src/Infrastructure/Domain/Event/Subscription/DAO/Subscription/Factory.php
@@ -15,9 +15,11 @@
 
 use Streak\Domain\Clock;
 use Streak\Domain\Event;
-use Streak\Infrastructure\Domain\Event\Subscription\DAO\Subscription;
+use Streak\Infrastructure\Domain\Event\Subscription\DAO;
 
 /**
+ * @implements Event\Subscription\Factory<DAO\Subscription>
+ *
  * @author Alan Gabriel Bem <alan.bem@gmail.com>
  *
  * @see \Streak\Infrastructure\Domain\Event\Subscription\DAO\Subscription\FactoryTest
@@ -28,8 +30,8 @@ public function __construct(private Clock $clock)
     {
     }
 
-    public function create(Event\Listener $listener): Event\Subscription
+    public function create(Event\Listener $listener): DAO\Subscription
     {
-        return new Subscription($listener, $this->clock);
+        return new DAO\Subscription($listener, $this->clock);
     }
 }
diff --git a/src/Infrastructure/Domain/Event/Subscription/DbalTransactionalSubscription/Factory.php b/src/Infrastructure/Domain/Event/Subscription/DbalTransactionalSubscription/Factory.php
index 86c89620..0fc0e64c 100644
--- a/src/Infrastructure/Domain/Event/Subscription/DbalTransactionalSubscription/Factory.php
+++ b/src/Infrastructure/Domain/Event/Subscription/DbalTransactionalSubscription/Factory.php
@@ -18,6 +18,8 @@
 use Streak\Infrastructure\Domain\Event\Subscription\DbalTransactionalSubscription;
 
 /**
+ * @implements Event\Subscription\Factory<DbalTransactionalSubscription>
+ *
  * @author Alan Gabriel Bem <alan.bem@gmail.com>
  *
  * @see \Streak\Infrastructure\Domain\Event\Subscription\DbalTransactionalSubscription\FactoryTest
@@ -35,7 +37,7 @@ public function __construct(private Event\Subscription\Factory $factory, private
         $this->maxTransactionSize = $maxTransactionSize;
     }
 
-    public function create(Event\Listener $listener): Event\Subscription
+    public function create(Event\Listener $listener): DbalTransactionalSubscription
     {
         $subscription = $this->factory->create($listener);
 
diff --git a/src/Infrastructure/Domain/EventBus/InMemoryEventBus.php b/src/Infrastructure/Domain/EventBus/InMemoryEventBus.php
index 1e12e4cc..01277abf 100644
--- a/src/Infrastructure/Domain/EventBus/InMemoryEventBus.php
+++ b/src/Infrastructure/Domain/EventBus/InMemoryEventBus.php
@@ -48,7 +48,7 @@ public function add(Event\Listener $listener): void
             }
         }
 
-        $this->listeners[] = $listener;
+        $this->listeners->enqueue($listener);
     }
 
     public function remove(Event\Listener $listener): void
diff --git a/src/Infrastructure/Domain/EventStore/DbalPostgresEventStore.php b/src/Infrastructure/Domain/EventStore/DbalPostgresEventStore.php
index 43ec1b1d..0bb95097 100644
--- a/src/Infrastructure/Domain/EventStore/DbalPostgresEventStore.php
+++ b/src/Infrastructure/Domain/EventStore/DbalPostgresEventStore.php
@@ -691,7 +691,7 @@ private function toRow(Event\Envelope $event): array
         ];
     }
 
-    private function extractIdForConcurrentWrite(UniqueConstraintViolationException $e)
+    private function extractIdForConcurrentWrite(UniqueConstraintViolationException $e): Domain\Id|null
     {
         // example:
         // SQLSTATE[23505]: Unique violation: 7 ERROR:  duplicate key value violates unique constraint "events_producer_type_producer_id_producer_version_key"
@@ -717,7 +717,7 @@ private function extractIdForConcurrentWrite(UniqueConstraintViolationException
         return $this->toId($matches['type'], $matches['id']);
     }
 
-    private function extractIdForEventAlreadyInStore(UniqueConstraintViolationException $e)
+    private function extractIdForEventAlreadyInStore(UniqueConstraintViolationException $e): UUID|null
     {
         // example:
         // SQLSTATE[23505]: Unique violation: 7 ERROR:  duplicate key value violates unique constraint "events_uuid_key"
diff --git a/src/Infrastructure/Domain/Serializer.php b/src/Infrastructure/Domain/Serializer.php
index a477381c..5fb5bccb 100644
--- a/src/Infrastructure/Domain/Serializer.php
+++ b/src/Infrastructure/Domain/Serializer.php
@@ -20,5 +20,5 @@ interface Serializer
 {
     public function serialize($subject): string;
 
-    public function unserialize($serialized);
+    public function unserialize(string $serialized);
 }
diff --git a/src/Infrastructure/Domain/Serializer/IGBinarySerializer.php b/src/Infrastructure/Domain/Serializer/IGBinarySerializer.php
index 5bccb1b5..59f824ae 100644
--- a/src/Infrastructure/Domain/Serializer/IGBinarySerializer.php
+++ b/src/Infrastructure/Domain/Serializer/IGBinarySerializer.php
@@ -27,7 +27,7 @@ public function serialize($subject): string
         return igbinary_serialize($subject);
     }
 
-    public function unserialize($serialized)
+    public function unserialize(string $serialized)
     {
         return igbinary_unserialize($serialized);
     }
diff --git a/src/Infrastructure/Domain/Serializer/PhpSerializer.php b/src/Infrastructure/Domain/Serializer/PhpSerializer.php
index f2873f25..d15f75b3 100644
--- a/src/Infrastructure/Domain/Serializer/PhpSerializer.php
+++ b/src/Infrastructure/Domain/Serializer/PhpSerializer.php
@@ -27,7 +27,7 @@ public function serialize($subject): string
         return serialize($subject);
     }
 
-    public function unserialize($serialized)
+    public function unserialize(string $serialized)
     {
         return unserialize($serialized);
     }
diff --git a/src/Infrastructure/Domain/Testing/AggregateRoot/TestCase.php b/src/Infrastructure/Domain/Testing/AggregateRoot/TestCase.php
index 7b187577..71e776cf 100644
--- a/src/Infrastructure/Domain/Testing/AggregateRoot/TestCase.php
+++ b/src/Infrastructure/Domain/Testing/AggregateRoot/TestCase.php
@@ -59,7 +59,7 @@ protected function createSnapshotterSerializer(): Serializer
         return new PhpSerializer();
     }
 
-    protected function createSnapshotterStorage()
+    protected function createSnapshotterStorage(): Snapshotter\Storage\InMemoryStorage
     {
         return new Snapshotter\Storage\InMemoryStorage();
     }
diff --git a/src/Infrastructure/Domain/Testing/Listener/TestCase.php b/src/Infrastructure/Domain/Testing/Listener/TestCase.php
index 903298ac..a227596e 100644
--- a/src/Infrastructure/Domain/Testing/Listener/TestCase.php
+++ b/src/Infrastructure/Domain/Testing/Listener/TestCase.php
@@ -38,7 +38,7 @@ public function given(Domain\Event ...$events): Scenario\When
 
     abstract public function createFactory(Application\CommandBus $bus): Domain\Event\Listener\Factory;
 
-    private function createScenario(Application\CommandBus $bus, Domain\Event\Listener\Factory $factory): Listener\Scenario
+    private function createScenario(SynchronousCommandBus $bus, Domain\Event\Listener\Factory $factory): Listener\Scenario
     {
         return new Listener\Scenario($bus, $factory);
     }
diff --git a/src/Infrastructure/Domain/UnitOfWork/SubscriptionDAOUnitOfWork.php b/src/Infrastructure/Domain/UnitOfWork/SubscriptionDAOUnitOfWork.php
index 186cfd3a..69f2b0ae 100644
--- a/src/Infrastructure/Domain/UnitOfWork/SubscriptionDAOUnitOfWork.php
+++ b/src/Infrastructure/Domain/UnitOfWork/SubscriptionDAOUnitOfWork.php
@@ -27,7 +27,7 @@
 class SubscriptionDAOUnitOfWork implements UnitOfWork
 {
     /**
-     * @var Subscription[]
+     * @var DAO\Subscription[]
      */
     private array $uncommited = [];
 
@@ -98,7 +98,7 @@ public function commit(): \Generator
 
             try {
                 while ($object = array_shift($this->uncommited)) {
-                    /** @var Subscription $object */
+                    /** @var DAO\Subscription $object */
                     try {
                         $this->dao->save($object);
 
@@ -125,16 +125,12 @@ public function clear(): void
 
     private function supports(object $subscription): bool
     {
-        if ($subscription instanceof DAO\Subscription) {
-            return true;
-        }
-
         while ($subscription instanceof Subscription\Decorator) {
             $subscription = $subscription->subscription();
+        }
 
-            if ($subscription instanceof DAO\Subscription) {
-                return true;
-            }
+        if ($subscription instanceof DAO\Subscription) {
+            return true;
         }
 
         return false;
diff --git a/tests/Domain/Event/EnvelopeTest.php b/tests/Domain/Event/EnvelopeTest.php
index d0624e6f..2a938761 100644
--- a/tests/Domain/Event/EnvelopeTest.php
+++ b/tests/Domain/Event/EnvelopeTest.php
@@ -127,29 +127,6 @@ public function testSettingEmptyAttributeName(): void
 
         $envelope->set('', 'value-1');
     }
-
-    public function nonScalarValues()
-    {
-        return [
-            [[]],
-            [new \stdClass()],
-        ];
-    }
-
-    /**
-     * @dataProvider nonScalarValues
-     *
-     * @param mixed $value
-     */
-    public function testSettingNonScalarAttribute($value): void
-    {
-        $envelope = Event\Envelope::new($this->event1, UUID::random(), \PHP_INT_MAX);
-
-        $exception = new \InvalidArgumentException('Value for attribute "attr-1" is a scalar.');
-        $this->expectExceptionObject($exception);
-
-        $envelope->set('attr-1', $value);
-    }
 }
 
 namespace Streak\Domain\Event\EnvelopeTest;
diff --git a/tests/Domain/EventSourcingTest.php b/tests/Domain/EventSourcingTest.php
index 85ac0bd0..bbe4da6e 100644
--- a/tests/Domain/EventSourcingTest.php
+++ b/tests/Domain/EventSourcingTest.php
@@ -637,7 +637,7 @@ class EventSourcedAggregateStub implements Event\Sourced\Aggregate
     use Aggregate\Identification;
 
     /**
-     * @var Event\Envelope[]
+     * @var array<int, Event\Envelope>
      */
     private array $appliedEvents = [];
 
@@ -671,12 +671,12 @@ public function appliedEvents(): array
 
     private function applyEvent1(Event1 $event): void
     {
-        $this->appliedEvents = [$event];
+        $this->appliedEvents[] = $event;
     }
 
     private function applyEvent2(Event2 $event): void
     {
-        $this->appliedEvents = [$event];
+        $this->appliedEvents[] = $event;
     }
 }
 
diff --git a/tests/Infrastructure/Domain/AggregateRoot/Snapshotter/Storage/PostgresStorageTest.php b/tests/Infrastructure/Domain/AggregateRoot/Snapshotter/Storage/PostgresStorageTest.php
index 28923a09..055f1311 100644
--- a/tests/Infrastructure/Domain/AggregateRoot/Snapshotter/Storage/PostgresStorageTest.php
+++ b/tests/Infrastructure/Domain/AggregateRoot/Snapshotter/Storage/PostgresStorageTest.php
@@ -15,7 +15,6 @@
 
 use Doctrine\DBAL\Connection;
 use Doctrine\DBAL\DriverManager;
-use Streak\Domain;
 use Streak\Domain\AggregateRoot;
 use Streak\Infrastructure\Domain\AggregateRoot\Snapshotter\Storage\Exception\SnapshotNotFound;
 
@@ -169,10 +168,12 @@ private function createAggregateRootStub(string $id): AggregateRoot
     }
 }
 
-class IdStub implements AggregateRoot\Id
+final class IdStub implements AggregateRoot\Id
 {
-    public function __construct(private string $id)
-    {
+    public function __construct(
+        /** @var non-empty-string $id */
+        private string $id
+    ) {
     }
 
     public function equals(object $object): bool
@@ -185,7 +186,7 @@ public function toString(): string
         return $this->id;
     }
 
-    public static function fromString(string $id): Domain\Id
+    public static function fromString(string $id): static
     {
         return new self($id);
     }
diff --git a/tests/Infrastructure/Domain/AggregateRoot/Snapshotter/Storage/RedisTest.php b/tests/Infrastructure/Domain/AggregateRoot/Snapshotter/Storage/RedisStorageTest.php
similarity index 74%
rename from tests/Infrastructure/Domain/AggregateRoot/Snapshotter/Storage/RedisTest.php
rename to tests/Infrastructure/Domain/AggregateRoot/Snapshotter/Storage/RedisStorageTest.php
index 3a52df2d..f66a8837 100644
--- a/tests/Infrastructure/Domain/AggregateRoot/Snapshotter/Storage/RedisTest.php
+++ b/tests/Infrastructure/Domain/AggregateRoot/Snapshotter/Storage/RedisStorageTest.php
@@ -23,7 +23,7 @@
  *
  * @covers \Streak\Infrastructure\Domain\AggregateRoot\Snapshotter\Storage\RedisStorage
  */
-class RedisTest extends Storage\TestCase
+class RedisStorageTest extends Storage\TestCase
 {
     public function testResetting(): void
     {
@@ -40,12 +40,27 @@ public function testResetting(): void
         $this->storage->find($this->aggregate1);
     }
 
+    public function testRedisInMultiMode(): void
+    {
+        $redis = $this->newRedis();
+        $storage = new RedisStorage($redis->multi());
+
+        $this->expectExceptionObject(new SnapshotNotFound($this->aggregate1));
+
+        $storage->find($this->aggregate1);
+    }
+
     protected function newStorage(): Storage
+    {
+        return new RedisStorage($this->newRedis());
+    }
+
+    private function newRedis(): \Redis
     {
         $redis = new \Redis();
         $redis->connect($_ENV['PHPUNIT_REDIS_HOSTNAME'], (int) $_ENV['PHPUNIT_REDIS_PORT']);
         $redis->select((int) $_ENV['PHPUNIT_REDIS_DATABASE']);
 
-        return new RedisStorage($redis);
+        return $redis;
     }
 }
diff --git a/tests/Infrastructure/Domain/Event/Subscription/EventSourcedRepositoryTest.php b/tests/Infrastructure/Domain/Event/Subscription/EventSourcedRepositoryTest.php
index 98bc5ef7..ad5cda86 100644
--- a/tests/Infrastructure/Domain/Event/Subscription/EventSourcedRepositoryTest.php
+++ b/tests/Infrastructure/Domain/Event/Subscription/EventSourcedRepositoryTest.php
@@ -243,7 +243,9 @@ public function testFindingSubscription(): void
             ->with(self::callback(function (Event\Stream $stream) use ($event1, $event2, $event3) {
                 $stream = iterator_to_array($stream);
 
-                return self::equalTo([$event1, $event2, $event3])->evaluate($stream);
+                self::equalTo([$event1, $event2, $event3])->evaluate($stream);
+
+                return true;
             }))
         ;
 
@@ -300,7 +302,9 @@ public function testFindingPreviouslyRestartedSubscription(): void
                 $stream = iterator_to_array($stream);
 
                 // streaming from SubscriptionRestarted event
-                return self::equalTo([$event1, $event2, $event3, $event4, $event5, $event6])->evaluate($stream);
+                self::equalTo([$event1, $event2, $event3, $event4, $event5, $event6])->evaluate($stream);
+
+                return true;
             }))
         ;
 
diff --git a/tests/Infrastructure/Domain/EventStore/EventStoreTestCase.php b/tests/Infrastructure/Domain/EventStore/EventStoreTestCase.php
index 0b6de8c2..a4e1ecb0 100644
--- a/tests/Infrastructure/Domain/EventStore/EventStoreTestCase.php
+++ b/tests/Infrastructure/Domain/EventStore/EventStoreTestCase.php
@@ -366,8 +366,10 @@ abstract protected function newEventStore(): EventStore;
 
 abstract class ValueId implements Domain\Id
 {
-    final public function __construct(private string $value)
-    {
+    final public function __construct(
+        /** @var non-empty-string $value */
+        private string $value
+    ) {
     }
 
     public function equals(object $id): bool
@@ -384,7 +386,7 @@ public function toString(): string
         return $this->value;
     }
 
-    public static function fromString(string $id): Domain\Id
+    public static function fromString(string $id): static
     {
         return new static($id);
     }