fix(core): preserve model request semantics (#30990)

packages/llm/src/protocols/openai-responses.ts

@@ -126,6 +126,7 @@ const OpenAIResponsesCoreFields = {
   tools: optionalArray(OpenAIResponsesTool),
   tool_choice: Schema.optional(OpenAIResponsesToolChoice),
   store: Schema.optional(Schema.Boolean),
+  service_tier: Schema.optional(OpenAIOptions.OpenAIServiceTier),
   prompt_cache_key: Schema.optional(Schema.String),
   include: optionalArray(OpenAIOptions.OpenAIResponseIncludable),
   reasoning: Schema.optional(
@@ -447,6 +448,7 @@ const lowerOptions = Effect.fn("OpenAIResponses.lowerOptions")(function* (reques
   const include = OpenAIOptions.include(request)
   const verbosity = OpenAIOptions.textVerbosity(request)
   const instructions = OpenAIOptions.instructions(request)
+  const serviceTier = OpenAIOptions.serviceTier(request)
   return {
     ...(instructions ? { instructions } : {}),
     ...(store !== undefined ? { store } : {}),
@@ -454,6 +456,7 @@ const lowerOptions = Effect.fn("OpenAIResponses.lowerOptions")(function* (reques
     ...(include ? { include } : {}),
     ...(effort || summary ? { reasoning: { effort, summary } } : {}),
     ...(verbosity ? { text: { verbosity } } : {}),
+    ...(serviceTier ? { service_tier: serviceTier } : {}),
   }
 })