From a35f96f427e93cdfbfa7882d0c5ff1de7402f8b5 Mon Sep 17 00:00:00 2001
From: Kit Langton <kit.langton@gmail.com>
Date: Fri, 28 Aug 2026 16:55:13 -0400
Subject: [PATCH] fix(core): preserve late opaque reasoning (#45694)

---
 .../openai-compatible-chat-language-model.ts  |  6 ++++-
 .../github-copilot/copilot-chat-model.test.ts | 26 +++++++++++++++++--
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/packages/core/src/github-copilot/chat/openai-compatible-chat-language-model.ts b/packages/core/src/github-copilot/chat/openai-compatible-chat-language-model.ts
index 6ad8757eb8a..de277fa69e9 100644
--- a/packages/core/src/github-copilot/chat/openai-compatible-chat-language-model.ts
+++ b/packages/core/src/github-copilot/chat/openai-compatible-chat-language-model.ts
@@ -653,7 +653,11 @@ export class OpenAICompatibleChatLanguageModel implements LanguageModelV3 {
             }
 
             if (isActiveText) {
-              controller.enqueue({ type: "text-end", id: "txt-0" })
+              controller.enqueue({
+                type: "text-end",
+                id: "txt-0",
+                providerMetadata: reasoningOpaque ? { copilot: { reasoningOpaque } } : undefined,
+              })
             }
 
             // go through all tool calls and send the ones that are not finished
diff --git a/packages/core/test/github-copilot/copilot-chat-model.test.ts b/packages/core/test/github-copilot/copilot-chat-model.test.ts
index bc1e2ecd956..0bc388787d5 100644
--- a/packages/core/test/github-copilot/copilot-chat-model.test.ts
+++ b/packages/core/test/github-copilot/copilot-chat-model.test.ts
@@ -244,14 +244,25 @@ describe("doStream", () => {
     expect(reasoningEndIndex).toBeLessThan(textStartIndex)
 
     // In this fixture, reasoning_opaque comes AFTER content has started (in chunk 4)
-    // So it arrives too late to be attached to reasoning-end. But it should still
-    // be captured and included in the finish event's providerMetadata.
+    // So it arrives too late to be attached to reasoning-end. It should still be
+    // captured on the completed text part and the finish event.
     const reasoningEnd = parts.find((p) => p.type === "reasoning-end")
     expect(reasoningEnd).toMatchObject({
       type: "reasoning-end",
       id: "reasoning-0",
     })
 
+    const textEnd = parts.find((p) => p.type === "text-end")
+    expect(textEnd).toEqual({
+      type: "text-end",
+      id: "txt-0",
+      providerMetadata: {
+        copilot: {
+          reasoningOpaque: "/PMlTqxqSJZnUBDHgnnJKLVI4eZQ",
+        },
+      },
+    })
+
     // reasoning_opaque should be in the finish event's providerMetadata
     const finish = parts.find((p) => p.type === "finish")
     expect(finish).toMatchObject({
@@ -305,6 +316,17 @@ describe("doStream", () => {
       },
     })
 
+    const textEnd = parts.find((p) => p.type === "text-end")
+    expect(textEnd).toEqual({
+      type: "text-end",
+      id: "txt-0",
+      providerMetadata: {
+        copilot: {
+          reasoningOpaque: "ExXaGwW7jBo39OXRe9EPoFGN1rOtLJBx",
+        },
+      },
+    })
+
     // Check text deltas
     const textDeltas = parts.filter((p) => p.type === "text-delta")
     expect(textDeltas).toHaveLength(2)