cmd/mbf: close on cancel completion

Like the previous change, this enables synchronisation on the client side via epoll.

Signed-off-by: Ophestra <cat@gensokyo.uk>

cmd/mbf/daemon.go

@@ -99,10 +99,9 @@ func cancelIdent(
 	var ident pkg.ID
 	if _, err := io.ReadFull(conn, ident[:]); err != nil {
 		return nil, false, errors.Join(err, conn.Close())
-	} else if err = conn.Close(); err != nil {
-		return nil, false, err
 	}
-	return &ident, cache.Cancel(unique.Make(ident)), nil
+	ok := cache.Cancel(unique.Make(ident))
+	return &ident, ok, conn.Close()
 }
 
 // serve services connections from a [net.UnixListener].
@@ -324,7 +323,10 @@ func cancelRemote(
 	} else if n != len(id) {
 		return errors.Join(io.ErrShortWrite, conn.Close())
 	}
-	return conn.Close()
+	if _, err = conn.Read(make([]byte, 1)); err == io.EOF {
+		err = nil
+	}
+	return errors.Join(err, conn.Close())
 }
 
 // abortRemote aborts all [pkg.Artifact] curing on a daemon.