Harden fail2ban integration and mark task complete

backend/app/utils/fail2ban_client.py

@@ -91,12 +91,9 @@ _RETRYABLE_ERRNOS: frozenset[int] = frozenset(
 _RETRY_MAX_ATTEMPTS: int = 3
 _RETRY_INITIAL_BACKOFF: float = 0.15  # seconds; doubles on each attempt
 
-# Maximum number of concurrent in-flight socket commands.  Operations that
-# exceed this cap wait until a slot is available.
+# Maximum number of concurrent in-flight socket commands per client.
+# Operations that exceed this cap wait until a slot is available.
 _COMMAND_SEMAPHORE_CONCURRENCY: int = 10
-# The semaphore is created lazily on the first send() call so it binds to the
-# event loop that is actually running (important for test isolation).
-_command_semaphore: asyncio.Semaphore | None = None
 
 
 class Fail2BanConnectionError(Exception):
@@ -266,6 +263,9 @@ class Fail2BanClient:
         """
         self.socket_path: str = socket_path
         self.timeout: float = timeout
+        self._command_semaphore: asyncio.Semaphore = asyncio.Semaphore(
+            _COMMAND_SEMAPHORE_CONCURRENCY
+        )
 
     async def send(self, command: Fail2BanCommand) -> object:
         """Send a command to fail2ban and return the response.
@@ -290,18 +290,14 @@ class Fail2BanClient:
                 connection is unexpectedly closed.
             Fail2BanProtocolError: If the response cannot be decoded.
         """
-        global _command_semaphore
-        if _command_semaphore is None:
-            _command_semaphore = asyncio.Semaphore(_COMMAND_SEMAPHORE_CONCURRENCY)
-
-        if _command_semaphore.locked():
+        if self._command_semaphore.locked():
             log.debug(
                 "fail2ban_command_waiting_semaphore",
                 command=command,
                 concurrency_limit=_COMMAND_SEMAPHORE_CONCURRENCY,
             )
 
-        async with _command_semaphore:
+        async with self._command_semaphore:
             log.debug("fail2ban_sending_command", command=command)
             loop: asyncio.AbstractEventLoop = asyncio.get_event_loop()
             try: