From 03317b7a45ccc1e03050a36783120f96dbb6be83 Mon Sep 17 00:00:00 2001
From: King Star <mcxin.y@gmail.com>
Date: Sun, 16 Aug 2026 22:03:04 +0800
Subject: [PATCH] fix: handle trailing newline in filesystem tail

---
 src/filesystem/__tests__/lib.test.ts | 27 +++++++++++++++++++++++++++
 src/filesystem/lib.ts                |  8 +++++++-
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/src/filesystem/__tests__/lib.test.ts b/src/filesystem/__tests__/lib.test.ts
index e0ae61224f..ec6a6b1e49 100644
--- a/src/filesystem/__tests__/lib.test.ts
+++ b/src/filesystem/__tests__/lib.test.ts
@@ -643,6 +643,33 @@ describe('Lib Functions', () => {
         expect(mockFileHandle.close).toHaveBeenCalled();
       });
 
+      it('ignores trailing newline when returning last lines', async () => {
+        const content = Buffer.from('line1\nline2\n');
+        mockFs.stat.mockResolvedValue({ size: content.length } as any);
+
+        const mockFileHandle = {
+          read: vi.fn(
+            (buffer: Buffer, offset: number, length: number, position: number) => {
+              const bytesRead = content.copy(
+                buffer,
+                offset,
+                position,
+                Math.min(position + length, content.length)
+              );
+              return Promise.resolve({ bytesRead });
+            }
+          ),
+          close: vi.fn().mockResolvedValue(undefined)
+        } as any;
+
+        mockFs.open.mockResolvedValue(mockFileHandle);
+
+        const result = await tailFile('/test/file.txt', 1);
+
+        expect(result).toBe('line2');
+        expect(mockFileHandle.close).toHaveBeenCalled();
+      });
+
       it('handles read errors gracefully', async () => {
         mockFs.stat.mockResolvedValue({ size: 100 } as any);
         
diff --git a/src/filesystem/lib.ts b/src/filesystem/lib.ts
index ce4af9f38a..763e145819 100644
--- a/src/filesystem/lib.ts
+++ b/src/filesystem/lib.ts
@@ -297,6 +297,7 @@ export async function tailFile(filePath: string, numLines: number): Promise<stri
     let chunk = Buffer.alloc(CHUNK_SIZE);
     let linesFound = 0;
     let remainingText = '';
+    let isLastChunk = true;
     
     // Read chunks from the end of the file until we have enough lines
     while (position > 0 && linesFound < numLines) {
@@ -311,7 +312,12 @@ export async function tailFile(filePath: string, numLines: number): Promise<stri
       const chunkText = readData + remainingText;
       
       // Split by newlines and count
-      const chunkLines = normalizeLineEndings(chunkText).split('\n');
+      const normalizedChunkText = normalizeLineEndings(chunkText);
+      const chunkLines = normalizedChunkText.split('\n');
+      if (isLastChunk && normalizedChunkText.endsWith('\n')) {
+        chunkLines.pop();
+      }
+      isLastChunk = false;
       
       // If this isn't the end of the file, the first line is likely incomplete
       // Save it to prepend to the next chunk