From cb1f961ea91ffcb341f36663544c7657afb6fc4a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pascal=20Andr=C3=A9?= <pascalandr@gmail.com>
Date: Fri, 21 Aug 2026 12:00:01 +0200
Subject: [PATCH] fix(chat): handle truncated diff headers

---
 .../chat/message/parts/ToolPart.test.ts       | 25 ++++++++++++++++++-
 .../components/chat/message/toolRenderers.tsx |  2 +-
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/packages/ui/src/components/chat/message/parts/ToolPart.test.ts b/packages/ui/src/components/chat/message/parts/ToolPart.test.ts
index 2faf34c3..d0697c59 100644
--- a/packages/ui/src/components/chat/message/parts/ToolPart.test.ts
+++ b/packages/ui/src/components/chat/message/parts/ToolPart.test.ts
@@ -2,7 +2,7 @@ import { describe, expect, test } from 'bun:test';
 
 import { getStreamingOutputAppend, getToolOutput, renderTerminalOutput } from './toolOutput';
 import { readTaskTagSessionIdFromOutput } from './taskSessionIdParser';
-import { tryParseJsonOutput } from '../toolRenderers';
+import { parseDiffToUnified, tryParseJsonOutput } from '../toolRenderers';
 import { getStreamingThrottleText } from '../../hooks/useStreamingTextThrottle';
 import { getToolDescriptionFallback } from './toolRenderUtils';
 
@@ -42,6 +42,29 @@ describe('getToolOutput', () => {
     });
 });
 
+describe('parseDiffToUnified', () => {
+    test('handles a streamed diff with a bare Index header', () => {
+        expect(parseDiffToUnified('Index:')).toEqual([]);
+        expect(parseDiffToUnified('Index:\n@@ -1,1 +1,1 @@\n-old\n+new')).toEqual([
+            {
+                file: 'file',
+                oldStart: 1,
+                newStart: 1,
+                lines: [
+                    { type: 'removed', lineNumber: 1, content: 'old' },
+                    { type: 'added', lineNumber: 1, content: 'new' },
+                ],
+            },
+        ]);
+    });
+
+    test('preserves spaces when extracting the indexed filename', () => {
+        const [hunk] = parseDiffToUnified('Index: src/my file.ts\n@@ -1,1 +1,1 @@\n-old\n+new');
+
+        expect(hunk?.file).toBe('my file.ts');
+    });
+});
+
 describe('renderTerminalOutput', () => {
     test('renders carriage-return progress updates as their latest value', () => {
         expect(renderTerminalOutput('Downloading 10%\r\u001B[2KDownloading 90%')).toBe('Downloading 90%');
diff --git a/packages/ui/src/components/chat/message/toolRenderers.tsx b/packages/ui/src/components/chat/message/toolRenderers.tsx
index 3c4dd773..3a5cd403 100644
--- a/packages/ui/src/components/chat/message/toolRenderers.tsx
+++ b/packages/ui/src/components/chat/message/toolRenderers.tsx
@@ -575,7 +575,7 @@ export const parseDiffToUnified = (diffText: string): UnifiedDiffHunk[] => {
 
         if (line.startsWith('Index:') || line.startsWith('===') || line.startsWith('---') || line.startsWith('+++')) {
             if (line.startsWith('Index:')) {
-                currentFile = line.split(' ')[1].split('/').pop() || 'file';
+                currentFile = line.slice('Index:'.length).trim().split('/').pop() || 'file';
             }
             i++;
             continue;