fix(openai): map system prompts to top-level instructions for ChatGPT auth requests

ts/smartai.middleware.openai.ts

@@ -0,0 +1,46 @@
+import type { JSONObject, LanguageModelV3CallOptions, LanguageModelV3Middleware } from '@ai-sdk/provider';
+
+const isNonEmptyString = (value: unknown): value is string => typeof value === 'string' && value.trim().length > 0;
+
+const getSystemInstructions = (prompt: LanguageModelV3CallOptions['prompt']): string | undefined => {
+  const instructions = prompt
+    .filter((message) => message.role === 'system')
+    .map((message) => message.content)
+    .filter(isNonEmptyString);
+
+  return instructions.length > 0 ? instructions.join('\n') : undefined;
+};
+
+/**
+ * ChatGPT's Codex backend requires top-level Responses API instructions.
+ * The standard OpenAI provider otherwise serializes system prompts as input items.
+ */
+export function createOpenAiChatGptInstructionsMiddleware(): LanguageModelV3Middleware {
+  return {
+    specificationVersion: 'v3',
+    transformParams: async ({ params }) => {
+      const instructions = getSystemInstructions(params.prompt);
+      if (!instructions) {
+        return params;
+      }
+
+      const providerOptions = params.providerOptions ?? {};
+      const openAiProviderOptions = providerOptions.openai ?? {};
+      if (isNonEmptyString(openAiProviderOptions.instructions)) {
+        return params;
+      }
+
+      return {
+        ...params,
+        prompt: params.prompt.filter((message) => message.role !== 'system'),
+        providerOptions: {
+          ...providerOptions,
+          openai: {
+            ...openAiProviderOptions,
+            instructions,
+          } as JSONObject,
+        },
+      } satisfies LanguageModelV3CallOptions;
+    },
+  };
+}