If I write a default message, can I have a way to have a placeholder for the username that will be replaced by the actual username when I post the message?

A message the mentions the username will be more efficient than one without it:

Thank you for your edits, keep going!
Thank you for your edits Kirsten, keep going!

{{ROOTPAGENAME}} could be used and it will work: if I post the message to user talk:Kirsten/Sandbox (random example to show how it works), the it will return Kirsten. But it is not intuitive to use.

If I write a default message, can I have a way to have a placeholder for the username that will be replaced by the actual username when I post the message?

I like that idea if it's relatively simple to implement (and can be done in a way that isn't confusing to the Mentor).

Some open questions for this task are:

1. Can we include a username that auto-populates in the default message?
2. We were exploring sending Mentors to the talk page directly (rather than reply from the Mentor dashboard) so they can see other talk page messages before posting, but if we are starting from a pre-populated new topic, then that's only true for users with "Enable quick topic adding" enabled in their Editing Preferences. How many users have that setting disabled?
3. How to handle if the talk page uses Flow/Structured Discussions?
4. We want to keep the initial iteration as simple as possible, and talk page UI can vary considerably based on user preferences... Would it make this task easier to keep the flow on the Mentor dashboard (and simply provide a prominent link to the Mentee's talk page within that flow).

Change 954967 had a related patch set uploaded (by Urbanecm; author: Urbanecm):

[mediawiki/extensions/GrowthExperiments@master] Personalized praise: Add a custom post sent message

https://gerrit.wikimedia.org/r/954967

This took a while, but should be ready for CR now.

Change 954967 merged by jenkins-bot:

[mediawiki/extensions/GrowthExperiments@master] Personalized praise: Add a custom post sent message

https://gerrit.wikimedia.org/r/954967

Checked in enwiki beta - works as expected:

@KStoller-WMF - questions:

• if a mentee has a Flow talk page, a mentor will be redirected there but without pre-filled text. Do we need a follow-up task to handle Flow boards?
• the message "Thanks for posting a message to your Mentee! Return to Mentor dashboard." is displayed for a rather short time.

{F41156329}

Thanks for testing, @Etonkovidova!

if a mentee has a Flow talk page, a mentor will be redirected there but without pre-filled text. Do we need a follow-up task to handle Flow boards?

Given the limited use of Flow and the long-term plans for Flow, I don't think a follow up task is needed. https://www.mediawiki.org/wiki/Structured_Discussions/Deprecation

the message "Thanks for posting a message to your Mentee! Return to Mentor dashboard." is displayed for a rather short time.

I just tested on Beta, and it seemed OK to me. I'll mark this task Resolved, but @JFernandez-WMF you should feel free to create a follow up task if you think we need to revisit the "Thanks for posting a message to your Mentee! Return to Mentor dashboard." confirmation message.