RTC: [Engine] Refreshing can cause a user to no longer update the document

[alecgeatches]

Description

Refreshing an open post can cause a user to become invisibly disconnected from a collaborative session:

Screen.Recording.2026-02-26.at.12.56.56.PM.mov

Step-by-step reproduction instructions

1. Enable real-time collaboration via WordPress Admin -> Settings -> Writing, and check the "Enable real-time collaboration" checkbox. Click the "Save Changes" button.
2. Open a post in tab A, then add a title and content and click "Save Draft".
3. In tab B, also open the post and add content. Both users should see the content synced.
4. Go back to tab A and refresh the page.
5. After refreshing, add more content in tab A. New content in tab A is no longer synced to other peers.

Note that the network panel still shows consistent REST calls to the /updates endpoint in tab A after it is invisibly disconnected from syncing.

Screenshots, screen recording, code snippet

No response

Environment info

No response

Please confirm that you have searched existing issues in the repo.

• Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

• Yes

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure

[alecgeatches]

Note that at the end of the reproduction above, user B (right-hand side) can still make edits to the document, and those will be reflected on user A's tab. However, any changes user A makes are not synced. It seems like user A is somehow in a read-only state where their write changes are ignored, but they're still able to pick up all of user B's changes.

[alecgeatches]

There's currently a branch with an end-to-end test to replicate this bug in add/rtc-refresh-disconnect-e2e-test: https://github.com/WordPress/gutenberg/compare/add/rtc-refresh-disconnect-e2e-test . It's actually passing in the e2e test currently but not manually, and that may be due to uses of createBlock instead of actual typing or similar not-exactly-real interactions. I'll keep working on that branch until I can replicate in an automated way.

EDIT: add/rtc-refresh-disconnect-e2e-test now reproduces the bug using actual document interactions.