fix(openai-codex): match codex replay identity

src/agents/openai-transport-stream.test.ts

@@ -1020,7 +1020,7 @@ describe("openai transport stream", () => {
     expect(params.max_output_tokens).toBe(65_536);
   });
 
-  it("uses top-level instructions for Codex responses and strips unsupported ChatGPT params", () => {
+  it("uses top-level instructions for Codex responses and preserves prompt cache identity", () => {
     const params = buildOpenAIResponsesParams(
       {
         id: "gpt-5.4",
@@ -1059,7 +1059,7 @@ describe("openai transport stream", () => {
     expect(params.input?.some((item) => item.role === "system" || item.role === "developer")).toBe(
       false,
     );
-    expect(params).not.toHaveProperty("prompt_cache_key");
+    expect(params.prompt_cache_key).toBe("session-123");
     expect(params.store).toBe(false);
     expect(params).not.toHaveProperty("metadata");
     expect(params).not.toHaveProperty("max_output_tokens");
@@ -1068,7 +1068,7 @@ describe("openai transport stream", () => {
     expect(params).not.toHaveProperty("temperature");
   });
 
-  it("sanitizes Codex responses params after payload hooks mutate them", () => {
+  it("sanitizes Codex responses params after payload hooks mutate them without stripping cache identity", () => {
     const payload = {
       model: "gpt-5.4",
       input: [],
@@ -1097,7 +1097,7 @@ describe("openai transport stream", () => {
       payload,
     );
 
-    expect(sanitized).not.toHaveProperty("prompt_cache_key");
+    expect(sanitized.prompt_cache_key).toBe("session-123");
     expect(sanitized).not.toHaveProperty("metadata");
     expect(sanitized).not.toHaveProperty("max_output_tokens");
     expect(sanitized).not.toHaveProperty("prompt_cache_retention");
@@ -1257,10 +1257,16 @@ describe("openai transport stream", () => {
         id?: string;
         call_id?: string;
         phase?: string;
+        encrypted_content?: string;
       }>;
     };
 
-    expect(params.input?.some((item) => item.type === "reasoning")).toBe(false);
+    const reasoningItem = params.input?.find((item) => item.type === "reasoning");
+    expect(reasoningItem).toMatchObject({
+      type: "reasoning",
+      encrypted_content: "ciphertext",
+    });
+    expect(reasoningItem?.id).toBeUndefined();
     const assistantMessage = params.input?.find(
       (item) => item.type === "message" && item.role === "assistant",
     );

src/agents/openai-transport-stream.ts

@@ -20,6 +20,7 @@ import type {
   ResponseInputItem,
   ResponseInputMessageContentList,
   ResponseOutputMessage,
+  ResponseReasoningItem,
 } from "openai/resources/responses/responses.js";
 import type { ModelCompatConfig } from "../config/types.models.js";
 import { createSubsystemLogger } from "../logging/subsystem.js";
@@ -60,6 +61,7 @@ const OPENAI_CODEX_RESPONSES_EMPTY_INPUT_TEXT = " ";
 const log = createSubsystemLogger("openai-transport");
 
 type ReplayableResponseOutputMessage = Omit<ResponseOutputMessage, "id"> & { id?: string };
+type ReplayableResponseReasoningItem = Omit<ResponseReasoningItem, "id"> & { id?: string };
 
 type BaseStreamOptions = {
   temperature?: number;
@@ -299,7 +301,13 @@ function convertResponsesMessages(
       for (const block of msg.content) {
         if (block.type === "thinking") {
           if (shouldReplayReasoningItems && block.thinkingSignature) {
-            output.push(JSON.parse(block.thinkingSignature));
+            const reasoningItem = JSON.parse(
+              block.thinkingSignature,
+            ) as ReplayableResponseReasoningItem;
+            if (!shouldReplayResponsesItemIds) {
+              delete reasoningItem.id;
+            }
+            output.push(reasoningItem as ResponseInputItem);
           }
         } else if (block.type === "text") {
           const textSignature = parseTextSignature(block.textSignature);
@@ -927,7 +935,6 @@ function usesNativeOpenAICodexResponsesBackend(model: Model<Api>): boolean {
 const OPENAI_CODEX_RESPONSES_UNSUPPORTED_PARAMS = [
   "max_output_tokens",
   "metadata",
-  "prompt_cache_key",
   "prompt_cache_retention",
   "service_tier",
   "temperature",
@@ -987,7 +994,7 @@ export function buildOpenAIResponsesParams(
     {
       includeSystemPrompt: !isCodexResponses,
       supportsDeveloperRole,
-      replayReasoningItems: !isNativeCodexResponses,
+      replayReasoningItems: true,
       replayResponsesItemIds: !isNativeCodexResponses,
     },
   );