diff --git a/open-sse/services/combo.js b/open-sse/services/combo.js
index 85a874b9..011b484c 100644
--- a/open-sse/services/combo.js
+++ b/open-sse/services/combo.js
@@ -52,11 +52,20 @@ export async function handleComboChat({ body, models, handleSingleModel, log })
     let errorText = result.statusText || "";
     try {
       const errorBody = await result.clone().json();
-      errorText = errorBody.error || errorBody.message || errorText;
+      errorText = errorBody?.error ?? errorBody?.message ?? errorText;
     } catch {
       // Ignore JSON parse errors
     }
 
+    // Normalize error text to string (Worker-safe)
+    if (typeof errorText !== "string") {
+      try {
+        errorText = JSON.stringify(errorText);
+      } catch {
+        errorText = String(errorText);
+      }
+    }
+
     // Check if should fallback to next model
     const { shouldFallback } = checkFallbackError(result.status, errorText);
     
diff --git a/open-sse/translator/request/claude-to-openai.js b/open-sse/translator/request/claude-to-openai.js
index 98d6006b..d9545933 100644
--- a/open-sse/translator/request/claude-to-openai.js
+++ b/open-sse/translator/request/claude-to-openai.js
@@ -3,7 +3,7 @@ import { FORMATS } from "../formats.js";
 import { adjustMaxTokens } from "../helpers/maxTokensHelper.js";
 
 // Convert Claude request to OpenAI format
-function claudeToOpenAIRequest(model, body, stream) {
+export function claudeToOpenAIRequest(model, body, stream) {
   const result = {
     model: model,
     messages: [],
diff --git a/open-sse/translator/request/gemini-to-openai.js b/open-sse/translator/request/gemini-to-openai.js
index 87f88839..5b3d0f01 100644
--- a/open-sse/translator/request/gemini-to-openai.js
+++ b/open-sse/translator/request/gemini-to-openai.js
@@ -3,7 +3,7 @@ import { FORMATS } from "../formats.js";
 import { adjustMaxTokens } from "../helpers/maxTokensHelper.js";
 
 // Convert Gemini request to OpenAI format
-function geminiToOpenAIRequest(model, body, stream) {
+export function geminiToOpenAIRequest(model, body, stream) {
   const result = {
     model: model,
     messages: [],
diff --git a/open-sse/translator/request/openai-responses.js b/open-sse/translator/request/openai-responses.js
index d2ffa54c..4467c8e7 100644
--- a/open-sse/translator/request/openai-responses.js
+++ b/open-sse/translator/request/openai-responses.js
@@ -10,7 +10,7 @@ import { FORMATS } from "../formats.js";
 /**
  * Convert OpenAI Responses API request to OpenAI Chat Completions format
  */
-function openaiResponsesToOpenAIRequest(model, body, stream, credentials) {
+export function openaiResponsesToOpenAIRequest(model, body, stream, credentials) {
   if (!body.input) return body;
 
   const result = { ...body };
@@ -134,7 +134,7 @@ function openaiResponsesToOpenAIRequest(model, body, stream, credentials) {
 /**
  * Convert OpenAI Chat Completions to OpenAI Responses API format
  */
-function openaiToOpenAIResponsesRequest(model, body, stream, credentials) {
+export function openaiToOpenAIResponsesRequest(model, body, stream, credentials) {
   const result = {
     model,
     input: [],
diff --git a/open-sse/translator/request/openai-to-claude.js b/open-sse/translator/request/openai-to-claude.js
index 3dd98ecc..8ab59187 100644
--- a/open-sse/translator/request/openai-to-claude.js
+++ b/open-sse/translator/request/openai-to-claude.js
@@ -7,7 +7,7 @@ import { adjustMaxTokens } from "../helpers/maxTokensHelper.js";
 const CLAUDE_OAUTH_TOOL_PREFIX = "proxy_";
 
 // Convert OpenAI request to Claude format
-function openaiToClaudeRequest(model, body, stream) {
+export function openaiToClaudeRequest(model, body, stream) {
   // Tool name mapping for Claude OAuth (capitalizedName → originalName)
   const toolNameMap = new Map();
   const result = {
diff --git a/open-sse/translator/request/openai-to-gemini.js b/open-sse/translator/request/openai-to-gemini.js
index fa6bde4e..e09b436a 100644
--- a/open-sse/translator/request/openai-to-gemini.js
+++ b/open-sse/translator/request/openai-to-gemini.js
@@ -191,12 +191,12 @@ function openaiToGeminiBase(model, body, stream) {
 }
 
 // OpenAI -> Gemini (standard API)
-function openaiToGeminiRequest(model, body, stream) {
+export function openaiToGeminiRequest(model, body, stream) {
   return openaiToGeminiBase(model, body, stream);
 }
 
 // OpenAI -> Gemini CLI (Cloud Code Assist)
-function openaiToGeminiCLIRequest(model, body, stream) {
+export function openaiToGeminiCLIRequest(model, body, stream) {
   const gemini = openaiToGeminiBase(model, body, stream);
   const isClaude = model.toLowerCase().includes("claude");
 
@@ -386,7 +386,7 @@ function wrapInCloudCodeEnvelopeForClaude(model, claudeRequest, credentials = nu
 }
 
 // OpenAI -> Antigravity (Sandbox Cloud Code with wrapper)
-function openaiToAntigravityRequest(model, body, stream, credentials = null) {
+export function openaiToAntigravityRequest(model, body, stream, credentials = null) {
   const isClaude = model.toLowerCase().includes("claude");
   
   if (isClaude) {
diff --git a/open-sse/translator/request/openai-to-kiro.js b/open-sse/translator/request/openai-to-kiro.js
index eb91d470..75ac04f6 100644
--- a/open-sse/translator/request/openai-to-kiro.js
+++ b/open-sse/translator/request/openai-to-kiro.js
@@ -230,7 +230,7 @@ function convertMessages(messages, tools, model) {
 /**
  * Build Kiro payload from OpenAI format
  */
-function buildKiroPayload(model, body, stream, credentials) {
+export function buildKiroPayload(model, body, stream, credentials) {
   const messages = body.messages || [];
   const tools = body.tools || [];
   const maxTokens = 32000;
@@ -278,5 +278,3 @@ function buildKiroPayload(model, body, stream, credentials) {
 }
 
 register(FORMATS.OPENAI, FORMATS.KIRO, buildKiroPayload, null);
-
-export { buildKiroPayload };
diff --git a/open-sse/translator/response/claude-to-openai.js b/open-sse/translator/response/claude-to-openai.js
index 3c2ce2d4..09ead173 100644
--- a/open-sse/translator/response/claude-to-openai.js
+++ b/open-sse/translator/response/claude-to-openai.js
@@ -17,7 +17,7 @@ function createChunk(state, delta, finishReason = null) {
 }
 
 // Convert Claude stream chunk to OpenAI format
-function claudeToOpenAIResponse(chunk, state) {
+export function claudeToOpenAIResponse(chunk, state) {
   if (!chunk) return null;
 
   const results = [];
diff --git a/open-sse/translator/response/gemini-to-openai.js b/open-sse/translator/response/gemini-to-openai.js
index 1a73b7ad..6abecaa6 100644
--- a/open-sse/translator/response/gemini-to-openai.js
+++ b/open-sse/translator/response/gemini-to-openai.js
@@ -2,7 +2,7 @@ import { register } from "../index.js";
 import { FORMATS } from "../formats.js";
 
 // Convert Gemini response chunk to OpenAI format
-function geminiToOpenAIResponse(chunk, state) {
+export function geminiToOpenAIResponse(chunk, state) {
   if (!chunk) return null;
   
   // Handle Antigravity wrapper
diff --git a/open-sse/translator/response/kiro-to-openai.js b/open-sse/translator/response/kiro-to-openai.js
index 5f3d136a..4fe0b624 100644
--- a/open-sse/translator/response/kiro-to-openai.js
+++ b/open-sse/translator/response/kiro-to-openai.js
@@ -9,7 +9,7 @@ import { FORMATS } from "../formats.js";
  * Parse Kiro SSE event and convert to OpenAI format
  * Kiro events: assistantResponseEvent, codeEvent, supplementaryWebLinksEvent, etc.
  */
-function convertKiroToOpenAI(chunk, state) {
+export function convertKiroToOpenAI(chunk, state) {
   
   if (!chunk) return null;
 
@@ -181,5 +181,3 @@ function convertKiroToOpenAI(chunk, state) {
 
 // Register translator
 register(FORMATS.KIRO, FORMATS.OPENAI, null, convertKiroToOpenAI);
-
-export { convertKiroToOpenAI };
diff --git a/open-sse/translator/response/openai-responses.js b/open-sse/translator/response/openai-responses.js
index 3596b5fc..9789bbbc 100644
--- a/open-sse/translator/response/openai-responses.js
+++ b/open-sse/translator/response/openai-responses.js
@@ -9,7 +9,7 @@ import { FORMATS } from "../formats.js";
  * Translate OpenAI chunk to Responses API events
  * @returns {Array} Array of events with { event, data } structure
  */
-function openaiToOpenAIResponsesResponse(chunk, state) {
+export function openaiToOpenAIResponsesResponse(chunk, state) {
   if (!chunk) {
     return flushEvents(state);
   }
@@ -359,7 +359,7 @@ function flushEvents(state) {
  * Translate OpenAI Responses API chunk to OpenAI Chat Completions format
  * This is for when Codex returns data and we need to send it to an OpenAI-compatible client
  */
-function openaiResponsesToOpenAIResponse(chunk, state) {
+export function openaiResponsesToOpenAIResponse(chunk, state) {
   if (!chunk) {
     // Flush: send final chunk with finish_reason
     if (!state.finishReasonSent && state.started) {
diff --git a/open-sse/translator/response/openai-to-claude.js b/open-sse/translator/response/openai-to-claude.js
index ca4270e7..ad625ed2 100644
--- a/open-sse/translator/response/openai-to-claude.js
+++ b/open-sse/translator/response/openai-to-claude.js
@@ -26,7 +26,7 @@ function stopTextBlock(state, results) {
 }
 
 // Convert OpenAI stream chunk to Claude format
-function openaiToClaudeResponse(chunk, state) {
+export function openaiToClaudeResponse(chunk, state) {
   if (!chunk || !chunk.choices?.[0]) return null;
 
   const results = [];
diff --git a/open-sse/utils/stream.js b/open-sse/utils/stream.js
index d3bd4289..76ab5521 100644
--- a/open-sse/utils/stream.js
+++ b/open-sse/utils/stream.js
@@ -2,6 +2,10 @@ import { translateResponse, initState } from "../translator/index.js";
 import { FORMATS } from "../translator/formats.js";
 import { saveRequestUsage, trackPendingRequest, appendRequestLog } from "@/lib/usageDb.js";
 
+// Singleton TextEncoder/Decoder for performance (reuse across all streams)
+const sharedDecoder = new TextDecoder();
+const sharedEncoder = new TextEncoder();
+
 // Get HH:MM:SS timestamp
 function getTimeString() {
   return new Date().toLocaleTimeString("en-US", { hour12: false, hour: "2-digit", minute: "2-digit", second: "2-digit" });
@@ -91,9 +95,9 @@ function logUsage(provider, usage, model = null, connectionId = null) {
   });
 }
 
-// Parse SSE data line
+// Parse SSE data line (optimized - reduce string operations)
 function parseSSELine(line) {
-  if (!line || !line.startsWith("data:")) return null;
+  if (!line || line.charCodeAt(0) !== 100) return null; // 'd' = 100
 
   const data = line.slice(5).trim();
   if (data === "[DONE]") return { done: true };
@@ -178,8 +182,6 @@ export function createSSEStream(options = {}) {
     connectionId = null
   } = options;
 
-  const decoder = new TextDecoder();
-  const encoder = new TextEncoder();
   let buffer = "";
   let usage = null;
 
@@ -188,7 +190,7 @@ export function createSSEStream(options = {}) {
 
   return new TransformStream({
     transform(chunk, controller) {
-      const text = decoder.decode(chunk, { stream: true });
+      const text = sharedDecoder.decode(chunk, { stream: true });
       buffer += text;
       reqLogger?.appendProviderChunk?.(text);
 
@@ -215,7 +217,7 @@ export function createSSEStream(options = {}) {
             output = line + "\n";
           }
           reqLogger?.appendConvertedChunk?.(output);
-          controller.enqueue(encoder.encode(output));
+          controller.enqueue(sharedEncoder.encode(output));
           continue;
         }
 
@@ -228,7 +230,7 @@ export function createSSEStream(options = {}) {
         if (parsed && parsed.done) {
           const output = "data: [DONE]\n\n";
           reqLogger?.appendConvertedChunk?.(output);
-          controller.enqueue(encoder.encode(output));
+          controller.enqueue(sharedEncoder.encode(output));
           continue;
         }
 
@@ -251,7 +253,7 @@ export function createSSEStream(options = {}) {
           for (const item of translated) {
             const output = formatSSE(item, sourceFormat);
             reqLogger?.appendConvertedChunk?.(output);
-            controller.enqueue(encoder.encode(output));
+            controller.enqueue(sharedEncoder.encode(output));
           }
         }
       }
@@ -260,7 +262,7 @@ export function createSSEStream(options = {}) {
     flush(controller) {
       trackPendingRequest(model, provider, connectionId, false);
       try {
-        const remaining = decoder.decode();
+        const remaining = sharedDecoder.decode();
         if (remaining) buffer += remaining;
 
         if (mode === STREAM_MODE.PASSTHROUGH) {
@@ -270,7 +272,7 @@ export function createSSEStream(options = {}) {
               output = "data: " + buffer.slice(5);
             }
             reqLogger?.appendConvertedChunk?.(output);
-            controller.enqueue(encoder.encode(output));
+            controller.enqueue(sharedEncoder.encode(output));
           }
           if (usage) {
             logUsage(provider, usage, model, connectionId);
@@ -299,7 +301,7 @@ export function createSSEStream(options = {}) {
               for (const item of translated) {
                 const output = formatSSE(item, sourceFormat);
                 reqLogger?.appendConvertedChunk?.(output);
-                controller.enqueue(encoder.encode(output));
+                controller.enqueue(sharedEncoder.encode(output));
               }
             }
           }
@@ -320,14 +322,14 @@ export function createSSEStream(options = {}) {
           for (const item of flushed) {
             const output = formatSSE(item, sourceFormat);
             reqLogger?.appendConvertedChunk?.(output);
-            controller.enqueue(encoder.encode(output));
+            controller.enqueue(sharedEncoder.encode(output));
           }
         }
 
         // Send [DONE] and log usage
         const doneOutput = "data: [DONE]\n\n";
         reqLogger?.appendConvertedChunk?.(doneOutput);
-        controller.enqueue(encoder.encode(doneOutput));
+        controller.enqueue(sharedEncoder.encode(doneOutput));
 
         if (state?.usage) {
           logUsage(state.provider || targetFormat, state.usage, model, connectionId);