docs: clarify in-memory client contracts

client.go

@@ -137,10 +137,12 @@ func newClient(options ...ClientOption) (*Client, error) {
 }
 
 // WithAuthDataChanged configures synchronous persistence for in-memory auth updates.
-// The callback runs under the client's internal login serialization. It must not
-// call Client methods other than AuthData or acquire a lock that may be held by any
-// goroutine calling Client. Callers must not call Client while holding a lock that
-// the callback may acquire. Returning an error leaves authentication unchanged.
+// The callback runs under the client's internal login serialization and must not
+// use Client directly or indirectly, including by waiting for a goroutine, future,
+// channel, or hook whose completion may call Client. It should perform only bounded,
+// standalone persistence and return. The callback and Client callers must obey lock
+// ordering: neither may hold a lock needed by the other. Returning an error leaves
+// authentication unchanged.
 func WithAuthDataChanged(callback func(AuthData) error) ClientOption {
 	return func(client *Client) error {
 		if callback == nil {