refactor(translator): P4 concern #5 buildUsage — apply to kiro/ollama/commandcode

- Replace 3 inline {prompt,completion,total} usage objects with buildUsage()
- Preserves ?? vs total fallback semantics (commandcode)
- Golden tests pass, identical output

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

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 { buildUsage } from "../helpers/usageHelper.js";
 import { reasoningDelta } from "../helpers/reasoningHelper.js";
 import { toOpenAIFinish } from "../concerns/finishReasonMap.js";
 
@@ -157,11 +158,12 @@ export function convertCommandCodeToOpenAI(chunk, state) {
       const finalChunk = makeChunk(state, {}, finishReason);
       const totalUsage = event.totalUsage || state.usage;
       if (totalUsage) {
-        finalChunk.usage = {
-          prompt_tokens: totalUsage.inputTokens ?? 0,
-          completion_tokens: totalUsage.outputTokens ?? 0,
-          total_tokens: totalUsage.totalTokens ?? ((totalUsage.inputTokens ?? 0) + (totalUsage.outputTokens ?? 0)),
-        };
+        const inTok = totalUsage.inputTokens ?? 0, outTok = totalUsage.outputTokens ?? 0;
+        finalChunk.usage = buildUsage({
+          promptTokens: inTok,
+          completionTokens: outTok,
+          totalTokens: totalUsage.totalTokens ?? (inTok + outTok),
+        });
       }
       out.push(finalChunk);
       break;

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

@@ -5,6 +5,7 @@
 import { register } from "../index.js";
 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";
 
@@ -143,11 +144,8 @@ export function convertKiroToOpenAI(chunk, state) {
   if (eventType === "usageEvent" || data.usageEvent) {
     const usage = data.usageEvent || data;
     if (usage && typeof usage === 'object') {
-      state.usage = {
-        prompt_tokens: usage.inputTokens || 0,
-        completion_tokens: usage.outputTokens || 0,
-        total_tokens: (usage.inputTokens || 0) + (usage.outputTokens || 0)
-      };
+      const inTok = usage.inputTokens || 0, outTok = usage.outputTokens || 0;
+      state.usage = buildUsage({ promptTokens: inTok, completionTokens: outTok, totalTokens: inTok + outTok });
     }
     return null;
   }

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

@@ -1,6 +1,7 @@
 import { register } from "../index.js";
 import { FORMATS } from "../formats.js";
 import { buildChunk } from "../helpers/chunkBuilder.js";
+import { buildUsage } from "../helpers/usageHelper.js";
 import { fallbackToolCallId } from "../helpers/toolCallHelper.js";
 
 /**
@@ -79,11 +80,8 @@ export function ollamaToOpenAI(chunk, state) {
  * Extract usage stats from Ollama response
  */
 function extractUsage(ollamaChunk) {
-  return {
-    prompt_tokens: ollamaChunk.prompt_eval_count || 0,
-    completion_tokens: ollamaChunk.eval_count || 0,
-    total_tokens: (ollamaChunk.prompt_eval_count || 0) + (ollamaChunk.eval_count || 0)
-  };
+  const inTok = ollamaChunk.prompt_eval_count || 0, outTok = ollamaChunk.eval_count || 0;
+  return buildUsage({ promptTokens: inTok, completionTokens: outTok, totalTokens: inTok + outTok });
 }
 
 /**