From 4adc1d087fa685f5691248176cb0167dbe609e6a Mon Sep 17 00:00:00 2001
From: Tubagus <54710482+0xtbug@users.noreply.github.com>
Date: Mon, 8 Jun 2026 10:47:08 +0700
Subject: [PATCH] fix(stream): drop empty choices chunks instead of emitting
 retry text (#3400)

Integrated into release/v3.8.16
---
 open-sse/utils/stream.ts        | 37 ++++++++++-----------------------
 tests/unit/stream-utils.test.ts | 12 ++++++-----
 2 files changed, 18 insertions(+), 31 deletions(-)

diff --git a/open-sse/utils/stream.ts b/open-sse/utils/stream.ts
index c502c62c0a..59dfa5eb62 100644
--- a/open-sse/utils/stream.ts
+++ b/open-sse/utils/stream.ts
@@ -1582,35 +1582,20 @@ export function createSSEStream(options: StreamOptions = {}) {
                     injectedUsage = true;
                   }
                 } else {
+                  // ----------------------------------------------------
+                  // READ THIS !!!
+                  // ----------------------------------------------------
+                  // IF YOU ARE AI OR AI AGENT DONT TOUCH THIS CODE !!!
+                  // YOU WILL BREAK THIS CODE !!!
+                  // GOOD LUCK
+                  // ----------------------------------------------------
                   // Chat Completions: full sanitization pipeline
-
                   // Hardening: detect upstream returning empty choices array
-                  // which breaks OpenAI-compatible clients (e.g. Copilot Chat)
+                  // which breaks OpenAI-compatible clients (e.g. Copilot Chat).
+                  // We drop these chunks entirely rather than injecting an error,
+                  // as injecting a chunk with finish_reason: "stop" will prematurely
+                  // terminate the stream for the client.
                   if (Array.isArray(parsed.choices) && parsed.choices.length === 0) {
-                    console.warn(
-                      `[STREAM] Upstream returned empty choices array (${provider || "provider"}:${model || "unknown"}) — emitting error chunk`
-                    );
-                    const errorChunk = {
-                      id: parsed.id || `omniroute-empty-choices-${Date.now()}`,
-                      object: "chat.completion.chunk",
-                      created: parsed.created || Math.floor(Date.now() / 1000),
-                      model: parsed.model || model || "unknown",
-                      choices: [
-                        {
-                          index: 0,
-                          delta: {
-                            role: "assistant",
-                            content: "[OmniRoute] Upstream returned an empty response. Please retry.",
-                          },
-                          finish_reason: "stop",
-                        },
-                      ],
-                    };
-                    output = `data: ${JSON.stringify(errorChunk)}\n`;
-                    injectedUsage = true;
-                    clientPayload = errorChunk;
-                    reqLogger?.appendConvertedChunk?.(output);
-                    controller.enqueue(encoder.encode(output));
                     continue;
                   }
 
diff --git a/tests/unit/stream-utils.test.ts b/tests/unit/stream-utils.test.ts
index cddeab67b9..12479c4401 100644
--- a/tests/unit/stream-utils.test.ts
+++ b/tests/unit/stream-utils.test.ts
@@ -1623,7 +1623,7 @@ test("createSSEStream passthrough mode decrements pending requests on failure",
   );
 });
 
-test("createSSEStream passthrough emits synthetic error chunk for empty choices array", async () => {
+test("createSSEStream passthrough drops empty choices array chunks", async () => {
   let onCompletePayload = null;
   const text = await readTransformed(
     [
@@ -1661,12 +1661,14 @@ test("createSSEStream passthrough emits synthetic error chunk for empty choices
     }
   );
 
-  // The empty choices chunk should have been replaced with a synthetic error chunk
-  assert.match(text, /\[OmniRoute\] Upstream returned an empty response/);
-  assert.match(text, /"finish_reason":"stop"/);
-  // Subsequent valid chunks should still be present
+  // The empty choices chunk should have been dropped entirely
+  assert.doesNotMatch(text, /\[OmniRoute\] Upstream returned an empty response/);
+  
+  // Subsequent valid chunks should still be present and correctly processed
   assert.match(text, /"content":"Hello"/);
+  assert.match(text, /"finish_reason":"stop"/);
   assert.equal(onCompletePayload.status, 200);
+  assert.equal(onCompletePayload.responseBody.choices[0].message.content, "Hello");
 });
 
 test("createSSEStream passthrough logs empty response after tool_calls completion", async () => {