fix(conventions): read the PR body file with utf-8-sig

A pull request body saved with a UTF-8 byte order mark starts with
U+FEFF before "### What", so the first heading is not recognised and the
checker reports the What section as missing. Decode the body file with
utf-8-sig so the mark is dropped and the sections are found.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V9UU71SP1UKGR51Sowbgmq

CMakeLists.txt

@@ -102,6 +102,8 @@ if(BUILD_TESTING)
         set_tests_properties(pad_input PROPERTIES TIMEOUT 20)
         add_test(NAME trace_digest COMMAND ${Python3_EXECUTABLE}
             ${CMAKE_CURRENT_SOURCE_DIR}/tools/tests/test_trace_digest.py)
+        add_test(NAME conventions_body_bom COMMAND ${Python3_EXECUTABLE}
+            ${CMAKE_CURRENT_SOURCE_DIR}/tools/tests/test_check_conventions_body_bom.py)
     endif()
 endif()
 

tools/check_conventions.py

@@ -397,5 +397,5 @@ if __name__ == "__main__":
     if pr:
         check.pull_request(pr["title"], pr["body"])
     elif args.title is not None or args.body:
-        check.pull_request(args.title or "", open(args.body, encoding="utf-8").read() if args.body else "")
+        check.pull_request(args.title or "", open(args.body, encoding="utf-8-sig").read() if args.body else "")
     raise SystemExit(output(check, os.environ.get("GITHUB_REPOSITORY", "boykopovar/AnyPS5")))

tools/tests/test_check_conventions_body_bom.py

@@ -0,0 +1,51 @@
+import os
+import subprocess
+import sys
+import tempfile
+import unittest
+from pathlib import Path
+
+BODY = (
+    "### What\nFix x.\n\n### Tested\nNot tested.\n\n### Checklist\n"
+    "- [x] Depends on: none\n- [x] AI-assisted: no\n"
+)
+
+
+class BodyBomTests(unittest.TestCase):
+    def run_checker(self, body):
+        checker = Path(__file__).resolve().parents[1] / "check_conventions.py"
+        with tempfile.TemporaryDirectory() as directory:
+            root = Path(directory)
+
+            def git(*args):
+                return subprocess.run(
+                    ["git", "-c", "user.name=Conventions Test", "-c", "user.email=test@example.com",
+                     "-c", "commit.gpgsign=false", *args],
+                    cwd=root, capture_output=True, text=True, check=True,
+                )
+
+            git("init", "-q")
+            (root / "README.md").write_text("# Example\n", encoding="utf-8")
+            git("add", ".")
+            git("commit", "-qm", "docs: add readme")
+            (root / "body.md").write_bytes(body)
+            return subprocess.run(
+                [sys.executable, "-I", str(checker), "--base", "HEAD", "--head", "HEAD",
+                 "--title", "fix: x", "--body", "body.md"],
+                cwd=root, capture_output=True, text=True, encoding="utf-8",
+                env={key: value for key, value in os.environ.items()
+                     if key not in ("GITHUB_EVENT_PATH", "GITHUB_STEP_SUMMARY", "GITHUB_ACTIONS")},
+            )
+
+    def test_body_with_utf8_bom_keeps_its_first_section(self):
+        result = self.run_checker(b"\xef\xbb\xbf" + BODY.encode("utf-8"))
+        self.assertNotIn("section 'What' is missing", result.stdout)
+        self.assertEqual(result.returncode, 0, result.stdout + result.stderr)
+
+    def test_body_without_bom_passes(self):
+        result = self.run_checker(BODY.encode("utf-8"))
+        self.assertEqual(result.returncode, 0, result.stdout + result.stderr)
+
+
+if __name__ == "__main__":
+    unittest.main()