Fix native reasoning passthrough history

Author: Codex

src/adapters/openai-responses.ts

@@ -22,6 +22,26 @@ export const FORWARD_HEADERS = [
   "x-responsesapi-include-timing-metrics",
 ];
 
+function sanitizeReasoningInputContent(body: unknown): unknown {
+  if (!body || typeof body !== "object" || Array.isArray(body)) return body;
+  const raw = body as Record<string, unknown>;
+  if (!Array.isArray(raw.input)) return body;
+
+  let changed = false;
+  const input = raw.input.map(item => {
+    if (!item || typeof item !== "object" || Array.isArray(item)) return item;
+    const rec = item as Record<string, unknown>;
+    if (rec.type !== "reasoning" || !Array.isArray(rec.content) || rec.content.length === 0) return item;
+    changed = true;
+    // Routed models can produce raw `reasoning_text` output items. Codex echoes those in later
+    // native GPT requests, but ChatGPT's Responses backend accepts reasoning input only with empty
+    // `content`; keep summaries/ids and drop the raw content so native passthrough does not 400.
+    return { ...rec, content: [] };
+  });
+
+  return changed ? { ...raw, input } : body;
+}
+
 export function createResponsesPassthroughAdapter(provider: OcxProviderConfig): ProviderAdapter & { passthrough: true } {
   return {
     name: "openai-responses",
@@ -49,7 +69,7 @@ export function createResponsesPassthroughAdapter(provider: OcxProviderConfig):
         url,
         method: "POST",
         headers,
-        body: JSON.stringify(parsed._rawBody),
+        body: JSON.stringify(sanitizeReasoningInputContent(parsed._rawBody)),
       };
     },
 

tests/openai-responses-passthrough.test.ts

@@ -0,0 +1,49 @@
+import { describe, expect, test } from "bun:test";
+import { createResponsesPassthroughAdapter } from "../src/adapters/openai-responses";
+
+const provider = {
+  adapter: "openai-responses",
+  baseUrl: "https://chatgpt.example/backend-api/codex",
+  authMode: "forward" as const,
+};
+
+describe("OpenAI Responses passthrough sanitization", () => {
+  test("drops raw reasoning input content before native GPT passthrough", () => {
+    const adapter = createResponsesPassthroughAdapter(provider);
+    const request = adapter.buildRequest({
+      modelId: "gpt-5.5",
+      context: { messages: [] },
+      stream: true,
+      options: {},
+      _rawBody: {
+        model: "gpt-5.5",
+        input: [
+          {
+            type: "reasoning",
+            id: "rs_1",
+            summary: [],
+            content: [{ type: "reasoning_text", text: "raw routed reasoning" }],
+          },
+          {
+            type: "message",
+            role: "user",
+            content: [{ type: "input_text", text: "hi" }],
+          },
+        ],
+      },
+    }, { headers: new Headers({ authorization: "Bearer token" }) });
+    const body = JSON.parse(request.body) as { input: Record<string, unknown>[] };
+
+    expect(body.input[0]).toMatchObject({
+      type: "reasoning",
+      id: "rs_1",
+      summary: [],
+      content: [],
+    });
+    expect(body.input[1]).toMatchObject({
+      type: "message",
+      role: "user",
+      content: [{ type: "input_text", text: "hi" }],
+    });
+  });
+});