feat: add settings caching middleware for API routes

lib/mastodon/middleware/load-settings.js

@@ -0,0 +1,35 @@
+/**
+ * Settings cache middleware for Mastodon API hot paths.
+ *
+ * Loads settings once per minute (not per request) and attaches
+ * to req.app.locals.apSettings for all downstream handlers.
+ */
+import { getSettings } from "../../settings.js";
+
+let cachedSettings = null;
+let cacheExpiry = 0;
+const CACHE_TTL = 60_000; // 1 minute
+
+export async function loadSettingsMiddleware(req, res, next) {
+  try {
+    const now = Date.now();
+    if (cachedSettings && now < cacheExpiry) {
+      req.app.locals.apSettings = cachedSettings;
+      return next();
+    }
+
+    const collections = req.app.locals.application?.collections;
+    cachedSettings = await getSettings(collections);
+    cacheExpiry = now + CACHE_TTL;
+    req.app.locals.apSettings = cachedSettings;
+    next();
+  } catch {
+    // On error, use defaults
+    if (!cachedSettings) {
+      const { DEFAULTS } = await import("../../settings.js");
+      cachedSettings = { ...DEFAULTS };
+    }
+    req.app.locals.apSettings = cachedSettings;
+    next();
+  }
+}

lib/mastodon/router.js

@@ -8,6 +8,7 @@
 import express from "express";
 import rateLimit from "express-rate-limit";
 import { corsMiddleware } from "./middleware/cors.js";
+import { loadSettingsMiddleware } from "./middleware/load-settings.js";
 import { tokenRequired, optionalToken } from "./middleware/token-required.js";
 import { errorHandler, notImplementedHandler } from "./middleware/error-handler.js";
 
@@ -77,6 +78,10 @@ export function createMastodonRouter({ collections, pluginOptions = {} }) {
   // ─── CORS ───────────────────────────────────────────────────────────────
   router.use("/api", corsMiddleware);
   router.use("/oauth/token", corsMiddleware);
+
+  // ─── Settings cache ────────────────────────────────────────────────────
+  // Loads plugin settings once per minute, available as req.app.locals.apSettings
+  router.use("/api", loadSettingsMiddleware);
   router.use("/oauth/revoke", corsMiddleware);
   router.use("/.well-known/oauth-authorization-server", corsMiddleware);