Add @mentions extraction service with tests

includes/Services/MentionService.php

@@ -0,0 +1,28 @@
+<?php
+
+namespace Escalated\Services;
+
+class MentionService
+{
+    private const MENTION_REGEX = '/@(\w+(?:\.\w+)*)/';
+
+    public static function extractMentions(?string $text): array
+    {
+        if (empty($text)) {
+            return [];
+        }
+        preg_match_all(self::MENTION_REGEX, $text, $matches);
+
+        return array_values(array_unique($matches[1] ?? []));
+    }
+
+    public static function extractUsernameFromEmail(string $email): string
+    {
+        if (empty($email)) {
+            return '';
+        }
+        $parts = explode('@', $email);
+
+        return $parts[0] ?? $email;
+    }
+}

tests/Test_Mention_Service.php

@@ -0,0 +1,49 @@
+<?php
+
+use Escalated\Services\MentionService;
+use PHPUnit\Framework\TestCase;
+
+class Test_Mention_Service extends TestCase
+{
+    public function test_single_mention()
+    {
+        $this->assertEquals(['john'], MentionService::extractMentions('Hello @john review'));
+    }
+
+    public function test_multiple_mentions()
+    {
+        $result = MentionService::extractMentions('@alice and @bob');
+        $this->assertContains('alice', $result);
+        $this->assertContains('bob', $result);
+    }
+
+    public function test_dotted_username()
+    {
+        $this->assertEquals(['john.doe'], MentionService::extractMentions('cc @john.doe'));
+    }
+
+    public function test_deduplicates()
+    {
+        $this->assertCount(1, MentionService::extractMentions('@alice @alice'));
+    }
+
+    public function test_empty()
+    {
+        $this->assertEmpty(MentionService::extractMentions(''));
+    }
+
+    public function test_null()
+    {
+        $this->assertEmpty(MentionService::extractMentions(null));
+    }
+
+    public function test_no_mentions()
+    {
+        $this->assertEmpty(MentionService::extractMentions('No mentions'));
+    }
+
+    public function test_username_from_email()
+    {
+        $this->assertEquals('john', MentionService::extractUsernameFromEmail('john@example.com'));
+    }
+}