fix: validate timeout is positive in connection, pool, and cluster

A timeout of 0 or negative makes every I/O operation fail immediately
with a confusing TimeoutError. Now raises ValueError with a clear
message at construction time.

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

Author: antoineleclair

src/dqliteclient/cluster.py

@@ -24,6 +24,8 @@ def __init__(
             node_store: Store for cluster node information
             timeout: Connection timeout in seconds
         """
+        if timeout <= 0:
+            raise ValueError(f"timeout must be positive, got {timeout}")
         self._node_store = node_store
         self._timeout = timeout
 

src/dqliteclient/connection.py

@@ -60,6 +60,8 @@ def __init__(
             database: Database name to open
             timeout: Connection timeout in seconds
         """
+        if timeout <= 0:
+            raise ValueError(f"timeout must be positive, got {timeout}")
         self._address = address
         self._database = database
         self._timeout = timeout

src/dqliteclient/pool.py

@@ -40,6 +40,8 @@ def __init__(
             raise ValueError(
                 f"min_size ({min_size}) must not exceed max_size ({max_size})"
             )
+        if timeout <= 0:
+            raise ValueError(f"timeout must be positive, got {timeout}")
 
         self._addresses = addresses
         self._database = database

tests/test_connection.py

@@ -49,6 +49,14 @@ def test_ipv6_no_port_raises(self) -> None:
 
 
 class TestDqliteConnection:
+    def test_zero_timeout_raises(self) -> None:
+        with pytest.raises(ValueError, match="timeout must be positive"):
+            DqliteConnection("localhost:9001", timeout=0)
+
+    def test_negative_timeout_raises(self) -> None:
+        with pytest.raises(ValueError, match="timeout must be positive"):
+            DqliteConnection("localhost:9001", timeout=-1)
+
     def test_init(self) -> None:
         conn = DqliteConnection("localhost:9001", database="test", timeout=5.0)
         assert conn.address == "localhost:9001"