From 7723e46c2697a1e89b697fb19685f6656d4931d1 Mon Sep 17 00:00:00 2001
From: AveryanAlex <alex@averyan.ru>
Date: Sun, 29 Mar 2026 00:23:54 +0300
Subject: [PATCH] =?UTF-8?q?fix:=20emit=20reasoning=5Fcontent=20in=20Respon?=
 =?UTF-8?q?ses=E2=86=92Chat=20streaming=20translation?=
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---
 .../translator/response/openai-responses.ts     | 17 ++++++++++++++---
 tests/unit/responses-translation-fixes.test.mjs | 17 ++++++++++++++++-
 2 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/open-sse/translator/response/openai-responses.ts b/open-sse/translator/response/openai-responses.ts
index 41e40e4f66..745b643de8 100644
--- a/open-sse/translator/response/openai-responses.ts
+++ b/open-sse/translator/response/openai-responses.ts
@@ -602,10 +602,21 @@ export function openaiResponsesToOpenAIResponse(chunk, state) {
     return null;
   }
 
-  // Reasoning events (convert to content or skip)
+  // Reasoning events — emit as reasoning_content in Chat format
   if (eventType === "response.reasoning_summary_text.delta") {
-    // Optionally include reasoning as content, or skip
-    return null;
+    const reasoningDelta = data.delta || "";
+    if (!reasoningDelta) return null;
+    return {
+      id: state.chatId,
+      object: "chat.completion.chunk",
+      created: state.created,
+      model: state.model || "gpt-4",
+      choices: [{
+        index: 0,
+        delta: { reasoning_content: reasoningDelta },
+        finish_reason: null,
+      }],
+    };
   }
 
   // Ignore other events
diff --git a/tests/unit/responses-translation-fixes.test.mjs b/tests/unit/responses-translation-fixes.test.mjs
index 20c827f96a..8ecf34f4bd 100644
--- a/tests/unit/responses-translation-fixes.test.mjs
+++ b/tests/unit/responses-translation-fixes.test.mjs
@@ -342,7 +342,7 @@ test("Chat→Responses: deprecated function role message converted to function_c
   assert.equal(fcOutput.call_id, fcItem.call_id);
 });
 
-const { openaiToOpenAIResponsesResponse } = await import(
+const { openaiToOpenAIResponsesResponse, openaiResponsesToOpenAIResponse } = await import(
   "../../open-sse/translator/response/openai-responses.ts"
 );
 const { initState } = await import("../../open-sse/translator/index.ts");
@@ -388,3 +388,18 @@ test("Chat→Responses streaming: completed event includes accumulated output",
   const msgOutput = completedEvent.data.response.output.find((o) => o.type === "message");
   assert.ok(msgOutput, "should have message output item");
 });
+
+test("Responses→Chat streaming: reasoning delta emits reasoning_content in Chat chunk", () => {
+  const state = { started: false, chatId: null, created: null, toolCallIndex: 0, finishReasonSent: false };
+
+  const chunk = {
+    type: "response.reasoning_summary_text.delta",
+    delta: "thinking step...",
+    item_id: "rs_1",
+    output_index: 0,
+    summary_index: 0,
+  };
+  const result = openaiResponsesToOpenAIResponse(chunk, state);
+  assert.ok(result, "should return a chunk");
+  assert.equal(result.choices[0].delta.reasoning_content, "thinking step...");
+});