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, 44 insertions, 0 deletions

diff --git a/src/util/file_watcher.cc b/src/util/file_watcher.cc
new file mode 100644
index 0000000..22eb824
--- /dev/null
+++ b/src/util/file_watcher.cc
@@ -0,0 +1,44 @@
+// file_watcher.cc - Hot-reload file change detection (debug only)
+
+#include "file_watcher.h"
+
+#if !defined(STRIP_ALL)
+
+#include <sys/stat.h>
+
+void FileWatcher::add_file(const char* path) {
+  WatchEntry entry;
+  entry.path = path;
+  entry.last_mtime = get_mtime(path);
+  entry.changed = false;
+  files_.push_back(entry);
+}
+
+bool FileWatcher::check_changes() {
+  bool any_changed = false;
+  for (auto& entry : files_) {
+    time_t current_mtime = get_mtime(entry.path.c_str());
+    if (current_mtime != entry.last_mtime && current_mtime != 0) {
+      entry.changed = true;
+      entry.last_mtime = current_mtime;
+      any_changed = true;
+    }
+  }
+  return any_changed;
+}
+
+void FileWatcher::reset() {
+  for (auto& entry : files_) {
+    entry.changed = false;
+  }
+}
+
+time_t FileWatcher::get_mtime(const char* path) {
+  struct stat st;
+  if (stat(path, &st) == 0) {
+    return st.st_mtime;
+  }
+  return 0;
+}
+
+#endif  // !defined(STRIP_ALL)