Resolve @handle owner/subscriber mentions in Slack web integration

[devin-ai-integration]

Summary

The alerts docs tell users to set owners/subscribers as @<email prefix> (e.g. owner: "@jessica.jones"). SlackWebMessagingIntegration only resolved full emails, through users.lookupByEmail, so any @handle went out as raw text inside a mrkdwn object. Slack sometimes auto-parses raw text like that. It appeared to in grouped-alert and resolved-reply lines, which use section text. It didn't in the single-alert Owners/Subscribers facts, which use section fields, so single alerts tagged nobody.

This PR resolves handles to user IDs explicitly. Every MentionBlock now renders as <@ID>, whatever block type it ends up in:

# send_message / reply_to_message
format_block_kit(body, self.resolve_user_id)   # was: self.get_user_id_from_email

def resolve_user_id(user):
    if user.startswith("@"):
        return self.get_user_id_from_handle(user[1:])   # new
    return self.get_user_id_from_email(user)            # unchanged

get_user_id_from_handle pages through users.list once per integration instance, on first use, and caches a handle -> user_id map. A handle matches, case-insensitively, either:

• the part of the user's email before the @ (what the docs describe), or
• their Slack username (name).

Collision rules:

• An email-prefix match wins over a username match.
• Full members win over guests (is_restricted / is_ultra_restricted).
• Among users at the same level, the first one listed wins.
• Bots and deleted users are skipped.

Failure handling:

• Mention resolution never blocks an alert. Any exception while listing users is logged and tracked, and handles not yet resolved stay plain text.
• The users listed so far are still cached, so a failing workspace isn't re-crawled for every mention.
• A repeated or non-string cursor stops pagination.
• If users are listed but none has a visible email (missing users:read.email scope), a warning is logged.

The users.list rate limiter (20/min) is created per instance, so separate environments don't share one budget.

Not changed:

• The legacy SlackIntegration path (_parse_emails_to_ids) still only handles emails.
• elementary-internal only picks this up once its elementary-data git pin is bumped.

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Thank you for raising your pull request.
Please make sure to add tests and document all user-facing changes.
You can do this by editing the docs files in this pull request.

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• elementary/messages/messaging_integrations/slack_web.py
• tests/unit/messages/messaging_integrations/test_slack_web.py

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📝 Walkthrough

Walkthrough

Slack Web messaging now resolves @handle references to Slack user IDs for messages and replies. It caches lookups from paginated Slack user listings and continues to use email lookup for other user references.

Changes

Slack handle resolution

Layer / File(s)	Summary
Build and cache handle lookup elementary/messages/messaging_integrations/slack_web.py, tests/unit/messages/messaging_integrations/test_slack_web.py	The integration builds a cached handle map from paginated Slack user listings. It skips bots and deleted users, and tests case-insensitive lookup, caching, and API errors.
Use resolved IDs for messages elementary/messages/messaging_integrations/slack_web.py, tests/unit/messages/messaging_integrations/test_slack_web.py	Message sending and replies now use the resolver for user references. A send-message test checks that a handle mention renders with the resolved Slack user ID.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~12 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to cd29c

Handle resolution preserves message delivery when Slack user listing fails. Partial results remain cached by design; unresolved handles stay plain text. The change is mergeable subject to normal checks.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 22 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: resolving @handle mentions to Slack users in the Slack web integration.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Inline comments:
Review comments at @elementary/messages/messaging_integrations/slack_web.py:
- Around line 214-218: Update the SlackApiError handler in the user-listing flow
so a failed users.list call does not return the partial user map; propagate the
failure so get_user_id_from_handle leaves the lookup uncached and can retry on a
later message.
- Around line 227-230: Update _iter_users to reject a next_cursor that matches
the current cursor, and catch that pagination ValueError in
_build_handle_to_user_id_map alongside SlackApiError so the existing
unresolved-handle fallback can continue sending the message.

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• elementary/messages/messaging_integrations/slack_web.py
• tests/unit/messages/messaging_integrations/test_slack_web.py

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[MikaKerman]

Without the users:read.email scope profile.email is absent, so only username matches would work and the docs' @<email prefix> form would silently not resolve. A one-line log when no user in the map has an email would make that easy to diagnose.

Follow-up: the legacy SlackIntegration._parse_emails_to_ids still leaves @handle as plain text. Worth a ticket so the two paths don't diverge.

[devin-ai-integration]

@MikaKerman Thanks. The missing-users:read.email warning is added in cd29c7c. I haven't filed a ticket for the legacy SlackIntegration._parse_emails_to_ids follow-up; this PR only touches the web integration. I can open one if you'd like.