From f816ffbd047346bce6353ec686ff26f6e1c4d7c7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=D0=94=D0=BC=D0=B8=D1=82=D1=80=D0=B8=D0=B9=20=D0=92=D0=BE?=
 =?UTF-8?q?=D0=BB=D0=BE=D0=B1=D1=83=D0=B5=D0=B2?=
 <77577658+simon100500@users.noreply.github.com>
Date: Mon, 16 Mar 2026 00:26:19 +0300
Subject: [PATCH] fix(pipeline): handle duplicate finish_reason chunks from
 OpenRouter
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Some OpenRouter model providers (e.g. google/gemini-3.1-flash-lite-preview)
send two consecutive SSE chunks with finish_reason='tool_calls'. The second
chunk arrives after streamingToolCallParser.reset() has been called, so it
carries empty parts — no functionCall entries.

The original handleChunkMerging treated every finish chunk as authoritative
and overwrote pendingFinishResponse, discarding the functionCall parts that
were correctly assembled from the first finish chunk.

Fix: when a second finish chunk arrives and a pendingFinishResponse already
exists, only merge usageMetadata (if present) and keep the candidates from
the first finish chunk.
---
 .../core/openaiContentGenerator/pipeline.ts   | 20 ++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/packages/core/src/core/openaiContentGenerator/pipeline.ts b/packages/core/src/core/openaiContentGenerator/pipeline.ts
index 5c6cdc6824..4e2d42bd80 100644
--- a/packages/core/src/core/openaiContentGenerator/pipeline.ts
+++ b/packages/core/src/core/openaiContentGenerator/pipeline.ts
@@ -255,9 +255,23 @@ export class ContentGenerationPipeline {
         .candidates?.[0]?.finishReason;
 
     if (isFinishChunk) {
-      // This is a finish reason chunk
-      collectedGeminiResponses.push(response);
-      setPendingFinish(response);
+      if (hasPendingFinish) {
+        // Duplicate finish chunk (e.g. from OpenRouter providers that send two
+        // finish_reason chunks for tool calls). The streaming tool call parser
+        // was already reset after the first finish chunk, so the second one
+        // carries no functionCall parts. Merge only usageMetadata and keep the
+        // candidates (including functionCall parts) from the first finish chunk.
+        const lastResponse =
+          collectedGeminiResponses[collectedGeminiResponses.length - 1];
+        if (response.usageMetadata) {
+          lastResponse.usageMetadata = response.usageMetadata;
+        }
+        setPendingFinish(lastResponse);
+      } else {
+        // This is a finish reason chunk
+        collectedGeminiResponses.push(response);
+        setPendingFinish(response);
+      }
       return false; // Don't yield yet, wait for potential subsequent chunks to merge
     } else if (hasPendingFinish) {
       // We have a pending finish chunk, merge this chunk's data into it