feat: Add debug-only file change detection for rapid iteration

Enables --hot-reload flag to watch config files and notify on changes.
Detects modifications to assets/sequences/music for rebuild workflow.
Completely stripped from release builds (0 bytes overhead).

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

1 files changed, 33 insertions, 0 deletions

diff --git a/src/util/file_watcher.h b/src/util/file_watcher.h
new file mode 100644
index 0000000..2766a43
--- /dev/null
+++ b/src/util/file_watcher.h
@@ -0,0 +1,33 @@
+// file_watcher.h - Hot-reload file change detection (debug only)
+
+#ifndef FILE_WATCHER_H_
+#define FILE_WATCHER_H_
+
+#if !defined(STRIP_ALL)
+
+#include <string>
+#include <vector>
+#include <ctime>
+
+class FileWatcher {
+ public:
+  FileWatcher() = default;
+
+  void add_file(const char* path);
+  bool check_changes();
+  void reset();
+
+ private:
+  struct WatchEntry {
+    std::string path;
+    time_t last_mtime;
+    bool changed;
+  };
+
+  std::vector<WatchEntry> files_;
+  time_t get_mtime(const char* path);
+};
+
+#endif  // !defined(STRIP_ALL)
+
+#endif  // FILE_WATCHER_H_