Fix critical race conditions and unsafe disk report command

lock_utils.py

@@ -1,4 +1,5 @@
 from pathlib import Path
+import os
 import time
 
 LOCK_DIR = Path("/var/run/tg-bot")
@@ -11,9 +12,14 @@ def lock_path(name: str) -> Path:
 
 def acquire_lock(name: str) -> bool:
     p = lock_path(name)
-    if p.exists():
+    try:
+        fd = os.open(str(p), os.O_CREAT | os.O_EXCL | os.O_WRONLY)
+    except FileExistsError:
         return False
-    p.write_text(str(time.time()))
+    try:
+        os.write(fd, str(time.time()).encode("ascii", errors="ignore"))
+    finally:
+        os.close(fd)
     return True