Visual glitches when sending multiple messages quickly

How to reproduce:
- make sure to copy a long text (for me it's usually an URL) into clipboard
- go into Keybase
- write something (in my case, sth like "here's the download link to the new version")
- press enter
- immediately after, press CTRL+V (paste) and press enter again

**Expected result:**
first line reads "here's the download link to the new version"
second line is the copy-pasted text

**Actual result:**
first line disappears, only second line is shown

After going into another chat and coming back, both lines are shown.

Start by reproducing the sequence in the Keybase chat composer: send a message, immediately paste a long clipboard value, and send it. Compare the visible conversation with the expected two lines, then switch chats and return to verify whether the first line reappears; done means both messages remain visible immediately after sending.

Written by the indexing model from the issue text.