refactor: add UserRateLimitEntry constructor and settings_changed method

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/src/app_state.rs

@@ -37,6 +37,25 @@ pub struct UserRateLimitEntry {
     pub limiter: RateLimiter,
 }
 
+impl UserRateLimitEntry {
+    /// Create a new entry, building the underlying rate limiter from the given settings.
+    pub fn new(max_requests: i32, window_seconds: i32) -> Self {
+        Self {
+            max_requests,
+            window_seconds,
+            limiter: RateLimiter::new(
+                max_requests as usize,
+                std::time::Duration::from_secs(window_seconds as u64),
+            ),
+        }
+    }
+
+    /// Returns `true` if the cached settings differ from the given values.
+    pub fn settings_changed(&self, max_requests: i32, window_seconds: i32) -> bool {
+        self.max_requests != max_requests || self.window_seconds != window_seconds
+    }
+}
+
 impl AppState {
     /// Create a new `AppState` instance.
     pub fn new(config: AppConfig, pool: PgPool, http_client: reqwest::Client) -> Self {

backend/src/services/synthesis.rs

@@ -397,26 +397,13 @@ fn get_user_rate_limiter(
         settings.rate_limit_time_window_seconds,
     ) {
         (Some(max_req), Some(window_sec)) => {
-            let mut entry = state.user_rate_limiters.entry(user_id).or_insert_with(|| {
-                UserRateLimitEntry {
-                    max_requests: max_req,
-                    window_seconds: window_sec,
-                    limiter: crate::services::rate_limiter::RateLimiter::new(
-                        max_req as usize,
-                        Duration::from_secs(window_sec as u64),
-                    ),
-                }
-            });
+            let mut entry = state
+                .user_rate_limiters
+                .entry(user_id)
+                .or_insert_with(|| UserRateLimitEntry::new(max_req, window_sec));
             // Replace if user's settings changed since the limiter was created
-            if entry.max_requests != max_req || entry.window_seconds != window_sec {
-                *entry = UserRateLimitEntry {
-                    max_requests: max_req,
-                    window_seconds: window_sec,
-                    limiter: crate::services::rate_limiter::RateLimiter::new(
-                        max_req as usize,
-                        Duration::from_secs(window_sec as u64),
-                    ),
-                };
+            if entry.settings_changed(max_req, window_sec) {
+                *entry = UserRateLimitEntry::new(max_req, window_sec);
             }
             Some(entry.limiter.clone())
         }