Studio: persist new sampling keys through settings sanitizer

Codex P1: the runtime store added frequencyPenalty, seed, stop,
serviceTier, parallelToolCalls but the save/load path went through
sanitizeInferenceParams, which only whitelisted the older numeric set
plus systemPrompt / trustRemoteCode. The new keys were silently
stripped on save and dropped on reload.

Extend the whitelist:
- frequencyPenalty added to the numeric finite-number set.
- seed: integer or explicit null (null = "no seed field on the wire").
- stop: string array, capped at 4 entries per OpenAI's limit.
- serviceTier: nullable enum (auto/default/flex/priority/scale).
- parallelToolCalls: boolean.

studio/frontend/src/features/chat/utils/chat-settings-storage.ts

@@ -40,10 +40,21 @@ const NUMERIC_INFERENCE_FIELDS = [
   "minP",
   "repetitionPenalty",
   "presencePenalty",
+  "frequencyPenalty",
   "maxSeqLength",
   "maxTokens",
 ] as const satisfies readonly (keyof PersistedInferenceParams)[];
 
+// `seed` is numeric but nullable (null = "no seed field on the wire") so
+// it can't go through the NUMERIC_INFERENCE_FIELDS Finite-number filter.
+const VALID_SERVICE_TIERS = new Set([
+  "auto",
+  "default",
+  "flex",
+  "priority",
+  "scale",
+]);
+
 const CHAT_PRESET_SOURCES = new Set<string>([
   "builtin-default",
   "custom",
@@ -140,6 +151,29 @@ function sanitizeInferenceParams(
   if (typeof value.trustRemoteCode === "boolean") {
     params.trustRemoteCode = value.trustRemoteCode;
   }
+  // seed: nullable integer (null = no seed on the wire).
+  if (value.seed === null) {
+    params.seed = null;
+  } else if (typeof value.seed === "number" && Number.isInteger(value.seed)) {
+    params.seed = value.seed;
+  }
+  // stop: capped string array per OpenAI's max-4 rule.
+  if (Array.isArray(value.stop)) {
+    const stops = value.stop.filter((s): s is string => typeof s === "string");
+    if (stops.length > 0) params.stop = stops.slice(0, 4);
+  }
+  // serviceTier: nullable enum string.
+  if (value.serviceTier === null) {
+    params.serviceTier = null;
+  } else if (
+    typeof value.serviceTier === "string" &&
+    VALID_SERVICE_TIERS.has(value.serviceTier)
+  ) {
+    params.serviceTier = value.serviceTier as PersistedInferenceParams["serviceTier"];
+  }
+  if (typeof value.parallelToolCalls === "boolean") {
+    params.parallelToolCalls = value.parallelToolCalls;
+  }
   return hasKeys(params) ? params : undefined;
 }