The server echo of an optimistic user message carries different part
ids, so the reducer dropped the optimistic part and appended the server
one at the end, and MessageBody keyed user parts by part id. The key
change remounted the text subtree (blank frame, markdown re-parse,
truncation state reset) and the append reordered text against file
parts.
Replace the optimistic part in place and key user parts positionally.
Bohdan Triapitsyn
cd46f0e3fb