diff --git a/.gitignore b/.gitignore
deleted file mode 100644
index 0031779..0000000
--- a/.gitignore
+++ /dev/null
@@ -1,54 +0,0 @@
-# Byte-compiled / optimized
-__pycache__/
-*.py[cod]
-*$py.class
-
-# Distribution / packaging
-dist/
-build/
-*.egg-info/
-*.egg
-
-# Virtual environments
-.venv/
-venv/
-env/
-
-# IDE
-.idea/
-.vscode/
-*.swp
-*.swo
-
-# Environment
-.env
-
-# Database
-*.db
-*.sqlite3
-
-# Local / generated artifacts
-.codex
-.claude/
-docs/internal/
-docs/OPTIMIZATION_ROADMAP.md
-docs/demo.cast
-reports/
-!docs/reports/
-docs/reports/*
-!docs/reports/showcase_*.md
-results/
-
-# Research papers (private, not for public distribution)
-papers/
-
-# OS
-.DS_Store
-Thumbs.db
-
-# Test cache
-.pytest_cache/
-.mypy_cache/
-.ruff_cache/
-htmlcov/
-.coverage
diff --git a/pyproject.toml b/pyproject.toml
index ac3b9c5..fed90f9 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -33,6 +33,7 @@ dependencies = [
     "pandas>=2.0",
     "pyyaml>=6.0",
     "tenacity>=8.2",
+    "filelock>=3.12",
 ]
 
 [project.optional-dependencies]
diff --git a/src/alphaevo/data/cache.py b/src/alphaevo/data/cache.py
index b2c3957..230da71 100644
--- a/src/alphaevo/data/cache.py
+++ b/src/alphaevo/data/cache.py
@@ -11,7 +11,6 @@
 from __future__ import annotations
 
 import contextlib
-import fcntl
 import logging
 import time
 from collections.abc import Iterator
@@ -20,6 +19,7 @@
 from pathlib import Path
 
 import pandas as pd  # type: ignore[import-untyped]
+from filelock import FileLock
 
 logger = logging.getLogger(__name__)
 
@@ -162,19 +162,15 @@ def put(self, symbol: str, start: date, end: date, df: pd.DataFrame) -> None:
     @staticmethod
     @contextmanager
     def _file_lock(target: Path) -> Iterator[None]:
-        """Acquire an exclusive file lock adjacent to *target*."""
+        """Acquire an exclusive file lock adjacent to *target* (cross-platform)."""
         lock_path = target.with_suffix(target.suffix + ".lock")
         lock_path.parent.mkdir(parents=True, exist_ok=True)
-        fd = lock_path.open("w")
-        try:
-            fcntl.flock(fd, fcntl.LOCK_EX)
+        lock = FileLock(str(lock_path))
+        with lock:
             yield
-        finally:
-            fcntl.flock(fd, fcntl.LOCK_UN)
-            fd.close()
-            # Best-effort cleanup; race with other processes is harmless
-            with contextlib.suppress(OSError):
-                lock_path.unlink()
+        # Best-effort cleanup; race with other processes is harmless
+        with contextlib.suppress(OSError):
+            lock_path.unlink()
 
     def invalidate(self, symbol: str | None = None) -> int:
         """Clear cached data.