feat(release): add reversible production cutover gates

apps/api/src/canary-gateway.ts

@@ -18,6 +18,7 @@ export const CANARY_DEFAULT_UPSTREAM_HOST = '127.0.0.1';
 export const CANARY_DEFAULT_UPSTREAM_PORT = 8790;
 
 const RESERVED_PORTS = new Set([8788, 8790]);
+export const PRODUCTION_GATEWAY_PORT = 8788;
 const BASE_HOP_BY_HOP_HEADERS = new Set([
   'connection',
   'keep-alive',
@@ -62,6 +63,8 @@ export interface CanaryGatewayOptions {
   readonly port?: number;
   readonly upstreamHost?: string;
   readonly upstreamPort?: number;
+  /** Set only after the production runtime validates its explicit acknowledgement. */
+  readonly ownsProductionPort?: boolean;
 }
 
 export interface CanaryGateway {
@@ -201,7 +204,7 @@ export function createCanaryGateway(options: CanaryGatewayOptions): CanaryGatewa
     throw new Error('Canary upstream must use a loopback host');
   }
   if (!Number.isInteger(port) || port < 0 || port > 65_535) throw new Error('Invalid canary port');
-  if (RESERVED_PORTS.has(port))
+  if (RESERVED_PORTS.has(port) && !(port === PRODUCTION_GATEWAY_PORT && options.ownsProductionPort))
     throw new Error(`Port ${port} is reserved and cannot run the canary`);
   if (!options.distDir) throw new Error('distDir is required');