Notifications: The table block fallback is incorrectly linked in certain circumstances.

[aerych]

Additional discussion and context can be found at p1626201873057800-slack-serenity

Steps to reproduce the behavior

An example post with comments illustrating the circumstance that leads to the glitch can be found at pcl4cA-wl-p2

1. User 1 should comment on a post. The comment should @ mentioning user two, then include a table block in the comment body.
2. User 2 should receive a notification about the comment. The notification should contain the table block fallback link instead of the table.
3. Checking the table block fall back link should show the following unintended behavior:
   • From the calypso master bar's notification panel, the link's href will be an empty string.
   • From a blog's master bar's notofication panel, the link's href will be something like https://widgets.wp.com/notifications/?v=@automattic/jetpack-blocks@13.1.0-12669-g727d23c131v2&locale=en
   • From the iOS mobile apps, the table block fallback text will not be linked.
4. Checking the JSON response from the /v1.1/notifications endpoint will show that the URL is an empty string.

What I expected to happen

The table block fallback should be correctly linked regardless of the @ mention preceding it in the comment body.

What actually happened

The table block fallback was incorrectly linked. Apparently due to being incorrectly parsed when the notification was built.

Context

See additional discussion and context at p1626201873057800-slack-serenity

Is this specific to the applied theme? Which one?

No

Does this happen on simple or atomic sites or both?

Both

Is there any console output or error text?

No.

Level of impact (Does it block purchases? Does it affect more than just one site?)

Bit of an edge case.

Screenshot / Video: If applicable, add screenshots to help explain your problem.

Example video is available at p1625786131336000-slack-wpmobile

[jordesign]

Closing as an edge case that hasn't had any attention or movement in 3+ years.