From 37d6464764ec3c5264ea31ddb45dbbc86d5f7c9d Mon Sep 17 00:00:00 2001
From: Aiden Cline <aidenpcline@gmail.com>
Date: Tue, 21 Jul 2026 21:10:50 -0500
Subject: [PATCH] fix(core): preserve patch parser leniency

---
 packages/core/test/patch.test.ts | 21 ++++++++++++++-------
 packages/util/src/patch.ts       |  2 +-
 2 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/packages/core/test/patch.test.ts b/packages/core/test/patch.test.ts
index f0b7a981b9..67d37e411c 100644
--- a/packages/core/test/patch.test.ts
+++ b/packages/core/test/patch.test.ts
@@ -185,6 +185,19 @@ describe("Patch", () => {
     ])
   })
 
+  test("allows an end-of-file marker before an explicit chunk", () => {
+    expect(
+      parse("*** Begin Patch\n*** Update File: file.txt\n*** End of File\n@@\n-old\n+new\n*** End Patch"),
+    ).toEqual([
+      {
+        type: "update",
+        path: "file.txt",
+        movePath: undefined,
+        chunks: [{ oldLines: ["old"], newLines: ["new"], changeContext: undefined }],
+      },
+    ])
+  })
+
   test("derives fuzzy line updates while preserving BOM", () => {
     const update = Patch.derive("update.txt", [{ oldLines: ["  old   "], newLines: ["new"] }], "\uFEFFold\n")
     expect(update).toEqual({ content: "new\n", bom: true })
@@ -388,16 +401,10 @@ describe("Patch", () => {
       ),
     ).toThrow("Invalid hunk at line 2: Update file hunk for path 'old.txt' is empty")
     expect(() => parse("*** Begin Patch\n*** Update File: file.txt\n*** End of File\n*** End Patch")).toThrow(
-      "Invalid hunk at line 3: Update hunk does not contain any lines",
+      "Invalid hunk at line 2: Update file hunk for path 'file.txt' is empty",
     )
   })
 
-  test("rejects an end-of-file marker before update lines", () => {
-    expect(() =>
-      parse("*** Begin Patch\n*** Update File: file.txt\n*** End of File\n@@\n-old\n+new\n*** End Patch"),
-    ).toThrow("Invalid hunk at line 3: Update hunk does not contain any lines")
-  })
-
   test("rejects an empty update chunk", () => {
     expect(() => parse("*** Begin Patch\n*** Update File: file.txt\n@@\n*** End Patch")).toThrow(
       "Invalid hunk at line 4: Update hunk does not contain any lines",
diff --git a/packages/util/src/patch.ts b/packages/util/src/patch.ts
index f4be526152..5744a108f3 100644
--- a/packages/util/src/patch.ts
+++ b/packages/util/src/patch.ts
@@ -167,7 +167,7 @@ function parseUpdate(
     }
     if (updateLine === "*** End of File") {
       const chunk = chunks.at(-1)
-      if (!chunk || (chunk.oldLines.length === 0 && chunk.newLines.length === 0)) {
+      if (chunk && chunk.oldLines.length === 0 && chunk.newLines.length === 0) {
         return {
           error: new InvalidHunkError({
             line: updateLine,