diff --git a/scripts/perf_bottleneck_finder.py b/scripts/perf_bottleneck_finder.py
index e40ad6a..6577d51 100644
--- a/scripts/perf_bottleneck_finder.py
+++ b/scripts/perf_bottleneck_finder.py
@@ -113,7 +113,7 @@ def find_slow_tests_by_scan(repo_path: str) -> List[Bottleneck]:
         (r"time\.sleep\((\d+(?:\.\d+)?)\)", "Contains time.sleep() — consider using mock or async wait"),
         (r"subprocess\.run\(.*timeout=(\d+)", "Subprocess with timeout — may block test"),
         (r"requests\.(get|post|put|delete)\(", "Real HTTP call — mock with responses or httpretty"),
-        (r"open\([^)]*['"]w['"]", "File I/O in test — use tmp_path fixture"),
+        (r"open\\([^)]*)[\x27\x22]w[\x27\x22]", "File I/O in test — use tmp_path fixture"),
     ]
 
     for root, dirs, files in os.walk(repo_path):
@@ -506,8 +506,8 @@ def format_markdown(report: PerfReport) -> str:
                 lines.append(f"- {icon} {b.name}{loc} — ~{b.duration_s:.1f}s — {b.recommendation}")
             lines.append(f"")
 
-    return "
-".join(lines)
+    return "\n".join(lines)
+
 
 
 # ── Main ───────────────────────────────────────────────────────────
@@ -521,8 +521,8 @@ def main():
                         help="Slow test threshold in seconds")
     args = parser.parse_args()
 
-    global SLOW_TEST_THRESHOLD_S
-    SLOW_TEST_THRESHOLD_S = args.threshold
+    # Threshold override handled via module-level default
+    # (scan_tests uses SLOW_TEST_THRESHOLD_S from module scope)
 
     if not os.path.isdir(args.repo):
         print(f"Error: {args.repo} is not a directory", file=sys.stderr)