fix(openai): strip non-msg item ids from passthrough message input

Drop agent_message ids during user-message conversion and guard native passthrough serialization against non-msg message ids.

Author: lidge-jun

src/adapters/openai-responses.ts

@@ -52,6 +52,23 @@ function sanitizeReasoningInputContent(body: unknown): unknown {
   return changed ? { ...raw, input } : body;
 }
 
+function stripInvalidMessageIds(body: unknown): unknown {
+  if (!isPlainObject(body) || !Array.isArray(body.input)) return body;
+
+  let changed = false;
+  const input = body.input.map(item => {
+    if (!isPlainObject(item) || item.type !== "message") return item;
+    if (typeof item.id === "string" && item.id.startsWith("msg_")) return item;
+    if (!("id" in item)) return item;
+    changed = true;
+    const next = { ...item };
+    delete next.id;
+    return next;
+  });
+
+  return changed ? { ...body, input } : body;
+}
+
 /**
  * Replace proxy-minted compaction items (`encrypted_content` starting with `ocx1:`) with plain
  * user messages before forwarding to the ChatGPT backend. Our envelope is transparent base64, not
@@ -282,7 +299,7 @@ export function createResponsesPassthroughAdapter(provider: OcxProviderConfig):
         url,
         method: "POST",
         headers,
-        body: JSON.stringify(stripUnsupportedHostedTools(sanitizeReasoningInputContent(scrubOcxCompactionItems(outBody)))),
+        body: JSON.stringify(stripInvalidMessageIds(stripUnsupportedHostedTools(sanitizeReasoningInputContent(scrubOcxCompactionItems(outBody))))),
       };
     },
 

src/server/responses.ts

@@ -346,9 +346,10 @@ export function sanitizeEncryptedContentInPlace(input: unknown): number {
           && (child as { type?: unknown }).type === "agent_message"
           && !hasEncryptedContentPart((child as { content?: unknown }).content)
         ) {
-          const message = child as { type: string; role?: string; author?: unknown; recipient?: unknown };
+          const message = child as { type: string; role?: string; id?: unknown; author?: unknown; recipient?: unknown };
           message.type = "message";
           message.role = "user";
+          delete message.id;
           delete message.author;
           delete message.recipient;
         }

tests/openai-responses-passthrough.test.ts

@@ -1,5 +1,6 @@
 import { describe, expect, test } from "bun:test";
 import { createResponsesPassthroughAdapter } from "../src/adapters/openai-responses";
+import { sanitizeEncryptedContentInPlace } from "../src/server/responses";
 
 const provider = {
   adapter: "openai-responses",
@@ -8,6 +9,50 @@ const provider = {
 };
 
 describe("OpenAI Responses passthrough sanitization", () => {
+  test("agent_message conversion removes its non-OpenAI item id", () => {
+    const input = [{
+      type: "agent_message",
+      id: "019f5e7f-ac31-7610-b69c-43ae41759fce",
+      author: "/root",
+      recipient: "/root/worker",
+      content: [{ type: "encrypted_content", encrypted_content: "delegated task" }],
+    }];
+
+    expect(sanitizeEncryptedContentInPlace(input)).toBe(1);
+    expect(input[0]).toEqual({
+      type: "message",
+      role: "user",
+      content: [{ type: "input_text", text: "delegated task" }],
+    });
+    expect(input[0]).not.toHaveProperty("id");
+  });
+
+  test("strips only non-msg ids from serialized message input items", () => {
+    const adapter = createResponsesPassthroughAdapter(provider);
+    const encryptedContent = "opaque-openai-encrypted-content";
+    const input = [
+      { type: "message", id: "019f5e7f-ac31-7610-b69c-43ae41759fce", role: "user", content: "first" },
+      { type: "message", id: "msg_abc", role: "assistant", content: "second" },
+      { type: "reasoning", id: "rs_1", summary: [], encrypted_content: encryptedContent },
+      { type: "function_call", id: "fc_1", call_id: "call_1", name: "ping", arguments: "{}" },
+      { type: "function_call_output", call_id: "call_1", output: "pong" },
+    ];
+    const request = adapter.buildRequest({
+      modelId: "gpt-5.5",
+      context: { messages: [] },
+      stream: true,
+      options: {},
+      _rawBody: { model: "gpt-5.5", input },
+    }, { headers: new Headers({ authorization: "Bearer token" }) });
+    const body = JSON.parse(request.body) as { input: Record<string, unknown>[] };
+
+    expect(body.input[0]).not.toHaveProperty("id");
+    expect(body.input[1].id).toBe("msg_abc");
+    expect(body.input[2]).toMatchObject({ id: "rs_1", encrypted_content: encryptedContent });
+    expect(body.input[3]).toMatchObject({ id: "fc_1", call_id: "call_1" });
+    expect(body.input[4]).toMatchObject({ type: "function_call_output", call_id: "call_1" });
+  });
+
   test("drops raw reasoning input content before native GPT passthrough", () => {
     const adapter = createResponsesPassthroughAdapter(provider);
     const request = adapter.buildRequest({