cardano-rpc: fix serverExceptionToClient for grapesy-1.2.0's ExactException

grapesy changed serverExceptionToClient's field type from SomeException
to ExactException (a newtype wrapper) between 1.1.1 and 1.2.0. This
repo's own pinned Hackage index-state (2026-08-02) predates that
release, so CI still resolves an older grapesy with the old signature;
a newer index-state (as used downstream by cardano-node) resolves
1.2.0 and this commit's serverExceptionToClient assignment fails to
typecheck. Unwrap via the ExactException pattern before using
fromException, as grapesy's own Server.Call/Context modules do
internally.

Author: erikd

cardano-rpc/src/Cardano/Rpc/Server.hs

@@ -52,6 +52,7 @@ import Network.GRPC.Server
 import Network.GRPC.Server.Protobuf
 import Network.GRPC.Server.Run
 import Network.GRPC.Server.StreamType
+import Network.GRPC.Util.Exception.Exact (ExactException (..))
 
 -- | gRPC method table for the @Node@ service.
 methodsNodeRpc
@@ -185,8 +186,8 @@ runRpcServer tracer rpcConfig networkMagic nodeKernelAccessRef = handleFatalExce
 
   -- Clients must never see internal error detail or call stacks; full detail is
   -- still traced server-side by 'topLevelHandler'.
-  exceptionToClient :: SomeException -> IO (Maybe Text)
-  exceptionToClient e =
+  exceptionToClient :: ExactException -> IO (Maybe Text)
+  exceptionToClient (WrapExactException e) =
     pure . Just $ maybe genericErrorMessage renderRpcExceptionForClient $ fromException e
    where
     genericErrorMessage = "Internal error while processing the request."