fix: remove dead _in_use set from ConnectionPool

The _in_use set was written to (add/discard) but never read anywhere
in the codebase. It was left behind after #080 removed force-closing
of in-use connections from close(). Remove the dead code to reduce
confusion and maintenance burden.

Fixes #105

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: antoineleclair

src/dqliteclient/pool.py

@@ -57,7 +57,6 @@ def __init__(
 
         self._cluster = ClusterClient.from_addresses(addresses, timeout=timeout)
         self._pool: asyncio.Queue[DqliteConnection] = asyncio.Queue(maxsize=max_size)
-        self._in_use: set[DqliteConnection] = set()
         self._size = 0
         self._lock = asyncio.Lock()
         self._closed = False
@@ -144,11 +143,9 @@ async def acquire(self) -> AsyncIterator[DqliteConnection]:
                 self._size -= 1
                 conn = await self._create_connection()
 
-        self._in_use.add(conn)
         try:
             yield conn
         except BaseException:
-            self._in_use.discard(conn)
             if conn.is_connected and not self._closed:
                 # Connection is healthy — user code raised a non-connection error.
                 # Return it to the pool instead of destroying it.
@@ -166,7 +163,6 @@ async def acquire(self) -> AsyncIterator[DqliteConnection]:
                 self._size -= 1
             raise
         else:
-            self._in_use.discard(conn)
             await self._release(conn)
 
     async def _release(self, conn: DqliteConnection) -> None:

tests/test_pool.py

@@ -561,6 +561,13 @@ async def slow_close():
             f"CancelledError during close() skipped _size decrement."
         )
 
+    async def test_pool_has_no_in_use_set(self) -> None:
+        """Pool should not maintain a dead _in_use set (removed as dead code)."""
+        pool = ConnectionPool(["localhost:9001"])
+        assert not hasattr(pool, "_in_use"), (
+            "Pool._in_use set should have been removed — it was dead code (written but never read)"
+        )
+
 
 class TestConnectionPoolIntegration:
     """Integration tests requiring mocked connections."""