Reconnect expired vSphere sessions instead of failing

ESXi expires idle SOAP sessions, after which the cached ServiceInstance
raised NotAuthenticated on every subsequent tool call until the server was
restarted. ConnectionManager.get now probes currentSession on cached
connections and rebuilds the connection (re-resolving datacenter, datastore,
network) when the session is dead.

src/mcvsphere/connection.py

@@ -61,6 +61,26 @@ class VMwareConnection:
         self._setup_datastore()
         self._setup_network()
 
+    def ensure_connected(self) -> None:
+        """Reconnect if the cached session has expired server-side.
+
+        ESXi expires idle SOAP sessions; the cached ``ServiceInstance`` then
+        raises ``NotAuthenticated`` on the next call. Probing ``currentSession``
+        is one cheap round-trip — None or a raised fault both mean "dead", so
+        we rebuild the connection (and re-resolve datacenter/datastore/etc).
+        """
+        try:
+            if (
+                self.si is not None
+                and self.content is not None
+                and self.content.sessionManager.currentSession is not None
+            ):
+                return  # session is alive
+        except Exception:
+            pass  # any fault here means the session is unusable
+        logger.info("vSphere session expired; reconnecting to %s", self.settings.vcenter_host)
+        self._connect()
+
     def _setup_datacenter(self) -> None:
         """Find and configure the target datacenter."""
         datacenters = [

src/mcvsphere/connection_manager.py

@@ -48,6 +48,9 @@ class ConnectionManager:
             self._connections[target] = VMwareConnection(
                 self._servers[target].to_settings(self._settings)
             )
+        else:
+            # Cached connection may have a server-expired session; revive it.
+            self._connections[target].ensure_connected()
         return self._connections[target]
 
     def describe(self) -> list[dict[str, Any]]: