Removes system message concept

docs/ARCHITECTURE.md

@@ -312,7 +312,7 @@ direction LR
             +withMessageParts(...MessagePart $part) self
             +withHistory(...Message $messages) self
             +usingModel(ModelInterface $model) self
-            +usingSystemInstruction(string|MessagePart[]|Message $systemInstruction) self
+            +usingSystemInstruction(string $systemInstruction) self
             +usingMaxTokens(int $maxTokens) self
             +usingTemperature(float $temperature) self
             +usingTopP(float $topP) self
@@ -475,7 +475,7 @@ direction LR
             +withMessageParts(...MessagePart $part) self
             +withHistory(...Message $messages) self
             +usingModel(ModelInterface $model) self
-            +usingSystemInstruction(string|MessagePart[]|Message $systemInstruction) self
+            +usingSystemInstruction(string $systemInstruction) self
             +usingMaxTokens(int $maxTokens) self
             +usingTemperature(float $temperature) self
             +usingTopP(float $topP) self
@@ -566,8 +566,6 @@ direction LR
         }
         class ModelMessage {
         }
-        class SystemMessage {
-        }
         class UserMessage {
         }
     }
@@ -582,7 +580,6 @@ direction LR
         class MessageRoleEnum {
             USER
             MODEL
-            SYSTEM
         }
         class ModalityEnum {
             TEXT
@@ -778,7 +775,6 @@ direction LR
     Candidate ..> FinishReasonEnum
     Message <|-- UserMessage
     Message <|-- ModelMessage
-    Message <|-- SystemMessage
     OperationInterface <|-- GenerativeAiOperation
     OperationInterface <|-- EmbeddingOperation
     ResultInterface <|-- GenerativeAiResult
@@ -944,8 +940,8 @@ direction LR
         class ModelConfig {
             +setOutputModalities(ModalityEnum[] $modalities) void
             +getOutputModalities() ModalityEnum[]
-            +setSystemInstruction(string|MessagePart|MessagePart[]|Message $systemInstruction) void
-            +getSystemInstruction() Message?
+            +setSystemInstruction(string $systemInstruction) void
+            +getSystemInstruction() string?
             +setCandidateCount(int $candidateCount) void
             +getCandidateCount() int
             +setMaxTokens(int $maxTokens) void

src/Messages/DTO/Message.php

@@ -142,8 +142,8 @@ final public static function fromArray(array $array): self
         } elseif ($role->isModel()) {
             return new ModelMessage($parts);
         } else {
-            // System is the only remaining option
-            return new SystemMessage($parts);
+            // Only USER and MODEL roles are supported
+            throw new \InvalidArgumentException('Invalid message role: ' . $role->value);
         }
     }
 }

src/Messages/Enums/MessageRoleEnum.php

@@ -13,10 +13,8 @@
  *
  * @method static self user() Creates an instance for USER role.
  * @method static self model() Creates an instance for MODEL role.
- * @method static self system() Creates an instance for SYSTEM role.
  * @method bool isUser() Checks if the role is USER.
  * @method bool isModel() Checks if the role is MODEL.
- * @method bool isSystem() Checks if the role is SYSTEM.
  */
 class MessageRoleEnum extends AbstractEnum
 {
@@ -29,9 +27,4 @@ class MessageRoleEnum extends AbstractEnum
      * Model role - messages from the AI model.
      */
     public const MODEL = 'model';
-
-    /**
-     * System role - system instructions.
-     */
-    public const SYSTEM = 'system';
 }

tests/unit/Messages/DTO/MessageTest.php

@@ -62,7 +62,7 @@ public function testCreateWithMultipleParts(): void
      */
     public function testCreateWithEmptyParts(): void
     {
-        $role = MessageRoleEnum::system();
+        $role = MessageRoleEnum::user();
         $message = new Message($role, []);
 
         $this->assertEquals($role, $message->getRole());
@@ -93,7 +93,6 @@ public function testWithDifferentRoles(MessageRoleEnum $role): void
     public function roleProvider(): array
     {
         return [
-            'system' => [MessageRoleEnum::system()],
             'user' => [MessageRoleEnum::user()],
             'model' => [MessageRoleEnum::model()],
         ];
@@ -151,7 +150,6 @@ public function testJsonSchema(): void
         $roleSchema = $schema['properties'][Message::KEY_ROLE];
         $this->assertEquals('string', $roleSchema['type']);
         $this->assertArrayHasKey('enum', $roleSchema);
-        $this->assertContains('system', $roleSchema['enum']);
         $this->assertContains('user', $roleSchema['enum']);
         $this->assertContains('model', $roleSchema['enum']);
 
@@ -263,21 +261,21 @@ public function testToArray(): void
     public function testFromArray(): void
     {
         $json = [
-            Message::KEY_ROLE => MessageRoleEnum::system()->value,
+            Message::KEY_ROLE => MessageRoleEnum::user()->value,
             Message::KEY_PARTS => [
                 [
                     MessagePart::KEY_TYPE => MessagePartTypeEnum::text()->value,
-                    MessagePart::KEY_TEXT => 'You are a helpful assistant.'
+                    MessagePart::KEY_TEXT => 'Hello, how can you help me?'
                 ]
             ]
         ];
 
         $message = Message::fromArray($json);
 
         $this->assertInstanceOf(Message::class, $message);
-        $this->assertEquals(MessageRoleEnum::system(), $message->getRole());
+        $this->assertEquals(MessageRoleEnum::user(), $message->getRole());
         $this->assertCount(1, $message->getParts());
-        $this->assertEquals('You are a helpful assistant.', $message->getParts()[0]->getText());
+        $this->assertEquals('Hello, how can you help me?', $message->getParts()[0]->getText());
     }
 
     /**