fix(openai): type service_tier in ws response schema

Declare service_tier on wsResponseCompletedEventSchema so the WS
Responses handler can read it without a double cast, mirroring the
pattern in responses/llm.ts. Fixes prettier line-length lint error.

Author: piyush-gambhir

plugins/openai/src/ws/llm.ts

@@ -584,7 +584,7 @@ export class WSLLMStream extends llm.LLMStream {
           promptTokens: event.response.usage.input_tokens,
           promptCachedTokens: event.response.usage.input_tokens_details.cached_tokens,
           totalTokens: event.response.usage.total_tokens,
-          serviceTier: (event.response as Record<string, unknown>).service_tier as string | undefined,
+          serviceTier: event.response.service_tier ?? undefined,
         },
       };
     }

plugins/openai/src/ws/types.ts

@@ -66,6 +66,7 @@ export const wsResponseCompletedEventSchema = z.object({
   response: z
     .object({
       id: z.string(),
+      service_tier: z.string().nullable().optional(),
       usage: z
         .object({
           output_tokens: z.number(),