Add real-time collaboration

It would be nice to show in the toolbar the ID of other connected users.

Will be done in #3535989: Add an ActiveUsers island

HTMX seems ready:

afaik the PR was actually not needed, I did some more testing and hx-swap-oob seems to work properly with hx-sse (using htmx 2.0.2 and htmx-ext-sse 2.2.2)

https://github.com/bigskysoftware/htmx-extensions/pull/94

Symfony has a nice API for this: https://symfony.com/blog/new-in-symfony-7-3-simpler-server-event-streaming

Le's do it

started by Pierre. Who want to continue?

Careful:

One thing to note about the HTMX SSE extension that I spent a full day troubleshooting is it doesn't handle multiline strings very well. This becomes a problem when the fragment you want to swap in has multiline hyperscript. I usually have to move it to the parent or convert to single line.

https://www.reddit.com/r/htmx/comments/1mjhzl1/gohtmx_server_sent_events...

For information, we have some moment where drag and/or drops from and/or to the root dropzone are not synched properly. After investigation, it seems this may not be related to this change.

However, by pushing the limit of the display builder events management, this change may help us to find already existing issues.

Something else to check before review

I need to talk with Grimreaper about 2 subjects:

• on my tests, sync works only from one user to the other one. Even when the second one init the builder.
• also, the HTTP endpoitn is disconnected and the request is resent at every cycle, instead of keeping a loooong connection. We may lose events because of that. It may be because of the return statemenst

I do some of the threads

Resolved some MR threads.

Only 2 left: https://git.drupalcode.org/project/display_builder/-/merge_requests/46/d...

• htmx_sse_local VS htmx_sse_cdn
• dependencies must be in /libraries for tests, so should be in .gitlab-ci.yml playwright test script.