There are two possibilities how comments can be moved to chatroom. Either a moderator moves them or the users who discuss in comments are offered to continue in chat - and if they choose this option, a chatroom is created.
Question. Is this recorded in some way in the timeline and the revision history? Is this recorded in SEDE? If not, is that intentional? Should it perhaps be added?
In Database schema documentation for the public data dump and SEDE (current revision), I saw as one of the possibilities of PostHistoryTypeId "31 = Comment discussion moved to chat". This fact suggests that it should be recorded in SEDE. At the same time, I do not see whether there is something in the Posthistory table for comments moved to chat by a moderator.
So I have tried to create a query returning posts with PostHistoryTypeId=31. To my surprise, I only got a single posts on Meta Stack Exchange. (Moreover, rene created a cross-site query which did not find any other posts in the whole network. You can see a brief discussion with rene in the SEDE chatroom.)
There is also a post on Meta Stack Overflow: SEDE query for # of conversations manually moved to chat seems low. In that posts result of some SEDE queries are discussed - however, in that post the queries were based on comments accompanying moving to chat.
Feature request. Include the events showing that messages were moved to chat to SEDE and timeline (revision list) - both for comments moved by moderators and rooms created by users.
I will freely admit that main reason for this post was my surprise that the documentation said that there is PostHistoryTypeId for such events and I did not find them. I was motivated mainly by curiosity. It is possible that there are some drawbacks to including such evens in SEDE and I simply did not think of them. But even if that's the case, it would be nice to hear the reasons why they are not included. (And maybe the database schema documentation should be updated - if some comments explaining this specific PostHistoryTypeId are needed.)
Here are some posts that I checked. (Although it is overly optimistic to make generalizations from a few posts.)
However, I have tried randomly finding some other post where comments were moved to chat. For example, this chatroom was imported from comments, and there is also a comment saying let's continue in chat. However, nothing about this is shown in the revisions, timeline, PostHistory
On the other hand, when I find some posts where the conversation was moved to chat by a moderator, this is displayed in the revision history and timeline. But there is not record in the PostHistory Table.