fix binary encoding issue

Author: dmcilvaney

.github/workflows/scripts/check_rendered_specs.py

@@ -365,7 +365,7 @@ def generate_patch(
     content_diffs: list[dict],
     extra_files: list[str],
     missing_files: list[str],
-) -> str:
+) -> bytes:
     """Generate a git patch covering all detected drift.
 
     Uses `git add -N` to mark untracked (extra) files as intent-to-add,
@@ -374,7 +374,7 @@ def generate_patch(
     """
     paths = [d["path"] for d in content_diffs] + extra_files + missing_files
     if not paths:
-        return ""
+        return b""
 
     # Mark untracked files as intent-to-add so git diff includes them
     if extra_files:
@@ -388,9 +388,14 @@ def generate_patch(
             pass
 
     try:
-        patch = _git("diff", "--", *paths)
+        result = subprocess.run(
+            ["git", "diff", "--", *paths],
+            capture_output=True,
+            check=True,
+        )
+        patch = result.stdout
     except subprocess.CalledProcessError:
-        patch = ""
+        patch = b""
 
     # Undo the intent-to-add so we don't leave index dirty
     if extra_files:
@@ -544,7 +549,7 @@ def main() -> int:
         patch_content = generate_patch(content_diffs, extra, missing)
         if patch_content:
             args.patch.parent.mkdir(parents=True, exist_ok=True)
-            args.patch.write_text(patch_content, encoding="utf-8")
+            args.patch.write_bytes(patch_content)
             print(f"Patch written to {args.patch}")
 
     # 4. Post comment or clean up (best-effort — exit code is authoritative)