Implement IMAP email-to-ticket gateway

RuntimeConfig.php

@@ -0,0 +1,44 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Box\Mod\Mailgateway;
+
+class RuntimeConfig
+{
+    public static function get(string $key): mixed
+    {
+        static $settings = null;
+        $settings ??= self::load(__DIR__ . '/config.php');
+        return $settings[$key] ?? throw new \RuntimeException('Unknown Mail Gateway operational setting: ' . $key);
+    }
+
+    public static function load(string $path): array
+    {
+        $settings = require $path;
+        if (!is_array($settings)) {
+            throw new \RuntimeException('Mail Gateway config.php must return an array');
+        }
+        foreach (['poll_interval_seconds', 'messages_per_mailbox', 'poll_budget_seconds',
+            'imap_timeout_seconds', 'max_message_bytes', 'max_ticket_body_bytes',
+            'notification_cooldown_seconds', 'composer_timeout_seconds'] as $key) {
+            if (!isset($settings[$key]) || !is_int($settings[$key]) || $settings[$key] < 1) {
+                throw new \RuntimeException('Mail Gateway config.php requires a positive integer for ' . $key);
+            }
+        }
+        if ($settings['max_ticket_body_bytes'] > 65535) {
+            throw new \RuntimeException('Mail Gateway ticket body limit cannot exceed 65535 bytes');
+        }
+        foreach (['php_cli_paths', 'composer_paths'] as $key) {
+            if (!isset($settings[$key]) || !is_array($settings[$key]) || $settings[$key] === []) {
+                throw new \RuntimeException('Mail Gateway config.php requires executable paths for ' . $key);
+            }
+            foreach ($settings[$key] as $value) {
+                if (!is_string($value) || !str_starts_with($value, '/') || str_contains($value, "\0")) {
+                    throw new \RuntimeException('Mail Gateway executable paths must be absolute paths');
+                }
+            }
+        }
+        return $settings;
+    }
+}