refactor(open-sse): add reasoningDelta helper, dedup thinking deltas (B4)

Centralize the reasoning_content delta shape (optional assistant role) used by
claude/gemini/kiro/codex/commandcode response translators. Keeps the cross-format
convention consistent for future translators. Output byte-for-byte identical;
golden + gate clean. Ollama left as-is (mutates existing delta object).

Co-authored-by: Cursor <cursoragent@cursor.com>

open-sse/translator/helpers/reasoningHelper.js

@@ -0,0 +1,6 @@
+// Build OpenAI delta carrying reasoning_content (optional leading assistant role)
+export function reasoningDelta(text, withRole = false) {
+  return withRole
+    ? { role: "assistant", reasoning_content: text }
+    : { reasoning_content: text };
+}

open-sse/translator/response/claude-to-openai.js

@@ -2,6 +2,7 @@ import { register } from "../index.js";
 import { FORMATS } from "../formats.js";
 import { buildChunk } from "../helpers/chunkBuilder.js";
 import { buildUsage } from "../helpers/usageHelper.js";
+import { reasoningDelta } from "../helpers/reasoningHelper.js";
 
 // Create OpenAI chunk helper
 function createChunk(state, delta, finishReason = null) {
@@ -67,7 +68,7 @@ export function claudeToOpenAIResponse(chunk, state) {
       if (delta?.type === "text_delta" && delta.text) {
         results.push(createChunk(state, { content: delta.text }));
       } else if (delta?.type === "thinking_delta" && delta.thinking) {
-        results.push(createChunk(state, { reasoning_content: delta.thinking }));
+        results.push(createChunk(state, reasoningDelta(delta.thinking)));
       } else if (delta?.type === "input_json_delta" && delta.partial_json) {
         const toolCall = state.toolCalls.get(chunk.index);
         if (toolCall) {

open-sse/translator/response/commandcode-to-openai.js

@@ -18,6 +18,7 @@
 import { register } from "../index.js";
 import { FORMATS } from "../formats.js";
 import { buildChunk } from "../helpers/chunkBuilder.js";
+import { reasoningDelta } from "../helpers/reasoningHelper.js";
 
 function ensureState(state, model) {
   if (!state.responseId) {
@@ -96,9 +97,7 @@ export function convertCommandCodeToOpenAI(chunk, state) {
       const text = event.text || "";
       if (!text) break;
       // Map reasoning to OpenAI "reasoning_content" field (used by deepseek-reasoner-style clients).
-      const delta = state.chunkIndex === 0
+      const delta = reasoningDelta(text, state.chunkIndex === 0);
-        ? { role: "assistant", reasoning_content: text }
-        : { reasoning_content: text };
       state.chunkIndex++;
       out.push(makeChunk(state, delta));
       break;

open-sse/translator/response/gemini-to-openai.js

@@ -2,6 +2,7 @@ import { register } from "../index.js";
 import { FORMATS } from "../formats.js";
 import { buildChunk } from "../helpers/chunkBuilder.js";
 import { buildUsage } from "../helpers/usageHelper.js";
+import { reasoningDelta } from "../helpers/reasoningHelper.js";
 
 // Build chunk meta for current gemini state
 function chunkMeta(state) {
@@ -42,7 +43,7 @@ export function geminiToOpenAIResponse(chunk, state) {
         if (hasTextContent) {
           results.push(buildChunk(
             chunkMeta(state),
-            isThought ? { reasoning_content: part.text } : { content: part.text },
+            isThought ? reasoningDelta(part.text) : { content: part.text },
             null
           ));
         }
@@ -78,7 +79,7 @@ export function geminiToOpenAIResponse(chunk, state) {
       if (part.text !== undefined && part.text !== "") {
         results.push(buildChunk(
           chunkMeta(state),
-          isThought ? { reasoning_content: part.text } : { content: part.text },
+          isThought ? reasoningDelta(part.text) : { content: part.text },
           null
         ));
       }

open-sse/translator/response/kiro-to-openai.js

@@ -6,6 +6,7 @@ import { register } from "../index.js";
 import { FORMATS } from "../formats.js";
 import { buildChunk } from "../helpers/chunkBuilder.js";
 import { fallbackToolCallId } from "../helpers/toolCallHelper.js";
+import { reasoningDelta } from "../helpers/reasoningHelper.js";
 
 // Build chunk meta for current kiro state
 function chunkMeta(state) {
@@ -94,10 +95,7 @@ export function convertKiroToOpenAI(chunk, state) {
       : (reasoning.text || reasoning.content || data.content || "");
     if (!content) return null;
 
-    const openaiChunk = buildChunk(chunkMeta(state), {
+    const openaiChunk = buildChunk(chunkMeta(state), reasoningDelta(content, state.chunkIndex === 0), null);
-      ...(state.chunkIndex === 0 ? { role: "assistant" } : {}),
-      reasoning_content: content
-    }, null);
 
     state.chunkIndex++;
     return openaiChunk;

open-sse/translator/response/openai-responses.js

@@ -7,6 +7,7 @@ import { FORMATS } from "../formats.js";
 import { buildChunk } from "../helpers/chunkBuilder.js";
 import { buildUsage } from "../helpers/usageHelper.js";
 import { fallbackToolCallId } from "../helpers/toolCallHelper.js";
+import { reasoningDelta } from "../helpers/reasoningHelper.js";
 
 /**
  * Translate OpenAI chunk to Responses API events
@@ -519,7 +520,7 @@ export function openaiResponsesToOpenAIResponse(chunk, state) {
     if (!delta) return null;
     return buildChunk(
       { id: state.chatId, created: state.created, model: state.model || "unknown" },
-      { reasoning_content: delta }
+      reasoningDelta(delta)
     );
   }