Slack adapter mention regex mangles email addresses

[thomasmol]

Bug Description

The regex /(?<!<)@(\w+)/g in packages/adapter-slack/src/markdown.ts converts @word to <@word> for Slack mentions. The lookbehind only excludes < before @, so email addresses like user@example.com get rewritten to user<@example>.com. This also breaks <mailto:user@example.com> links.

chat/packages/adapter-slack/src/markdown.ts

Lines 41 to 43 in 1c12d33

	private convertMentionsToSlack(text: string): string {
	return text.replace(/(?<!<)@(\w+)/g, "<@$1>");
	}

Steps to Reproduce

Post a message containing an email address through the Slack adapter:
await adapter.postChannelMessage('slack:C1234', 'Contact user@example.com for help');

Expected Behavior

Slack displays: Contact user@example.com for help with the email auto-linked.

Actual Behavior

Slack displays: Contact user@example.com for help with @example rendered as a broken user mention, because the text sent to Slack is Contact user<@example>.com for help.

This also affects mailto: links — mailto:user@example.com becomes <mailto:user<@example>.com>.

Code Sample

Chat SDK Version

4.26

Node.js Version

24

Platform Adapter

Slack

Operating System

macOS

Additional Context

Potential fix is to add \w to the lookbehind:
/(?<![<\w])@(\w+)/g