✨(backend) email thread participants on reply

[AntoLC]

Purpose

Participants of a comment thread were never told about a reply unless they were mentioned. They now get an email when someone answers in a thread they take part in.

Proposal

• Recipients: the thread creator, the authors of earlier comments and the users mentioned in the thread, minus the reply author. Only active users with an explicit access allowed to comment (same rule as mentions); users the author just mentioned are skipped as the mention email covers them
• Queue the email in a Celery task so SMTP stays out of the request; queuing is best effort and never fails the creation of the comment
• Guard against duplicate emails when a task is delivered twice, and a failing recipient does not block the others
• Throttle a conversation per recipient: a user is emailed at most once per THREAD_REPLY_NOTIFICATION_COOLDOWN_MINUTES in a thread (default 15, 0 disables). The delay is per user, so a participant who was not emailed yet is never silenced by the emails sent to the others: A creates a thread, B replies and A is emailed, A replies 5 minutes later and B is emailed (A is not, again). The delay is fixed from the email, the following replies do not extend it, so an active thread cannot keep a user uninformed. It is released when the email could not be sent

New env

docs/src/backend/impress/settings.py

Lines 531 to 536 in 00b98d4

	# Comment threads
	THREAD_REPLY_NOTIFICATION_COOLDOWN_MINUTES = values.IntegerValue(
	15,
	environ_name="THREAD_REPLY_NOTIFICATION_COOLDOWN_MINUTES",
	environ_prefix=None,
	)

Email Demo

Known limitations

• A user who was just emailed does not get another email for the replies posted during their delay. The email only links to the document, so they see everything when they open it, but they are not told that newer replies exist.
• A user mentioned by the reply author in the thread, within MENTION_NOTIFICATION_COOLDOWN_MINUTES, is skipped because the mention email covers them. If that mention email was itself suppressed by the mention cooldown, the user gets neither email.

Possible follow-up: a "seen" notion

Both limitations (and the repeated mention of a user in the same context within the mention cooldown) come from throttling on time only. We could throttle on whether the user has seen the thread instead:

• Record when each user last saw a thread (one row per (thread, user) with last_seen_at; a user's own reply counts as seen).
• On a reply, queue one delayed task per recipient, with a countdown of THREAD_REPLY_NOTIFICATION_COOLDOWN_MINUTES. When it runs, send the email only if the user has not seen the thread since the comment was created, and was not already emailed about an earlier unseen reply.
• Open question, how to detect "seen": mark the thread as seen when its comments are fetched (backend only, cheap but approximate, since the frontend refetches threads on a ping and a background tab would count), or an explicit POST threads/{id}/seen/ called when the thread is displayed (accurate, but needs a small frontend change and has to work with the offline queue).
• Trade-offs: a new model and migration, a rework of the notification task, and an email a few minutes after the reply instead of immediately.

[virgile-dev]

• Do we have a link that open the comment modal and scrolls to the right spot ?

For the email content this is my suggestion.

Subject: {{User_name}} replied to a comment in "{{document_title}}"

Title:
{{User_name}} replied to a comment in the following document:
{{document_title}}

Button: {{Open}}

Docs: Your essential tool for organizing, sharing, and collaborating on documents as a team.

A solution by La Suite Numérique.

[AntoLC]

Do we have a link that open the comment modal and scrolls to the right spot ?

I added a commit frontend side to do it.

Docs: Your essential tool for organizing, sharing, and collaborating on documents as a team.

A solution by La Suite Numérique.

I updated the main email message.
The part mentioned is not modified, I suggest that we change it in another PR because it is not directly linked to this PR, all the email have this message, it will probably break lot of tests.

[github-actions]

Size Change: +1 kB (+0.02%)

Total Size: 4.06 MB

📦 View Changed

Filename	Size	Change
apps/impress/out/_next/static/7cceab40/_buildManifest.js	697 B	+697 B (new file)	🆕
apps/impress/out/_next/static/chunks/1519.js	69 kB	+636 B (+0.93%)
apps/impress/out/_next/static/chunks/2253.js	0 B	-284 kB (removed)	🏆
apps/impress/out/_next/static/chunks/6277.js	0 B	-156 kB (removed)	🏆
apps/impress/out/_next/static/chunks/7064.js	283 kB	+283 kB (new file)	🆕
apps/impress/out/_next/static/chunks/7986.js	157 kB	+157 kB (new file)	🆕
apps/impress/out/_next/static/eea248e3/_buildManifest.js	0 B	-701 B (removed)	🏆

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