fix: clarify apply-patch delete-file misuse

scripts/src/apply-patch-v2.ts

@@ -188,8 +188,13 @@ export function parseApplyPatchV2(patchText: string): PatchParseResult {
       continue;
     }
     if (line.startsWith(deleteFileMarker)) {
-      hunks.push({ kind: "delete", path: validatePatchPath(line.slice(deleteFileMarker.length), index + 1) });
+      const filePath = validatePatchPath(line.slice(deleteFileMarker.length), index + 1);
       index += 1;
+      const nextContentIndex = nextNonBlankLineIndex(lines, index, lines.length - 1);
+      if (nextContentIndex < lines.length - 1 && !isFileHeader(lines[nextContentIndex] ?? "")) {
+        throw invalidDeleteFileLineError(lines[nextContentIndex] ?? "", nextContentIndex + 1, filePath);
+      }
+      hunks.push({ kind: "delete", path: filePath });
       continue;
     }
     if (line.startsWith(updateFileMarker)) {
@@ -240,6 +245,26 @@ function invalidAddFileLineError(lineText: string, line: number, filePath: strin
   );
 }
 
+function invalidDeleteFileLineError(lineText: string, line: number, filePath: string): ApplyPatchV2Error {
+  const details = { line, path: filePath, text: lineText };
+  if (lineText.trimStart().startsWith("@@")) {
+    return new ApplyPatchV2Error(
+      "invalid delete file line: remove @@ for Delete File. Delete File sections contain only the `*** Delete File: <path>` header; do not include hunk markers or file content.",
+      details,
+    );
+  }
+  return new ApplyPatchV2Error(
+    "invalid delete file line: Delete File sections contain only the `*** Delete File: <path>` header. Remove old file content lines such as -old line.",
+    details,
+  );
+}
+
+function nextNonBlankLineIndex(lines: string[], start: number, endExclusive: number): number {
+  let index = start;
+  while (index < endExclusive && (lines[index] ?? "").trim().length === 0) index += 1;
+  return index;
+}
+
 export function deriveUpdatedContent(filePath: string, originalContent: string, chunks: UpdateChunk[]): PatchUpdateResult {
   const originalLines = splitContentLines(originalContent);
   const replacements = computeReplacements(filePath, originalLines, chunks);