make the cap of `activeRateLimitRequests` match the rate limit

It's trivial to have more than 128 requests in flight: open a busy
timeline, scroll a bit down, wait for many notes to arrive, scroll to
the top. The frontend will send "subscribe to note" messages for each
new note that it accumulated, all at once. We don't want to shut down
the connection in those common cases!

packages/backend/src/server/api/StreamingApiServerService.ts

@@ -151,7 +151,7 @@ export class StreamingApiServerService {
 				return this.rateLimitThis(user, requestIp, {
 					key: 'wsmessage',
 					duration: ms('2sec'),
-					max: 4090,
+					max: 4096,
 				});
 			};
 

packages/backend/src/server/api/stream/Connection.ts

@@ -120,7 +120,9 @@ export default class Connection {
 		if (this.closingConnection) return;
 
 		if (this.rateLimiter) {
-			if (this.activeRateLimitRequests <= 128) {
+			// this 4096 should match the `max` of the `rateLimiter`, see
+			// StreamingApiServerService
+			if (this.activeRateLimitRequests <= 4096) {
 				this.activeRateLimitRequests++;
 				const shouldRateLimit = await this.rateLimiter();
 				this.activeRateLimitRequests--;