Move the older dehydrated devices behind a config flag

synapse/config/experimental.py

@@ -35,6 +35,10 @@ def read_config(self, config: JsonDict, **kwargs: Any) -> None:
         # MSC2285 (unstable private read receipts)
         self.msc2285_enabled: bool = experimental.get("msc2285_enabled", False)
 
+        # MSC2697 (device dehydration)
+        # Enabled by default since this option was added after adding the feature.
+        self.msc2697_enabled: bool = experimental.get("msc2697_enabled", True)
+
         # MSC3244 (room version capabilities)
         self.msc3244_enabled: bool = experimental.get("msc3244_enabled", True)
 

synapse/rest/client/devices.py

@@ -331,5 +331,6 @@ def register_servlets(hs: "HomeServer", http_server: HttpServer) -> None:
     DeleteDevicesRestServlet(hs).register(http_server)
     DevicesRestServlet(hs).register(http_server)
     DeviceRestServlet(hs).register(http_server)
-    DehydratedDeviceServlet(hs).register(http_server)
-    ClaimDehydratedDeviceServlet(hs).register(http_server)
+    if hs.config.experimental.msc2697_enabled:
+        DehydratedDeviceServlet(hs).register(http_server)
+        ClaimDehydratedDeviceServlet(hs).register(http_server)