Bot mentions in blocks go undetected

[sentry-junior]

Junior's mention detection relies entirely on event.text, but bot messages built with Block Kit may carry the @mention only in event.blocks as a rich-text user element — never serialized into event.text. Since Slack also does not fire app_mention for bot-to-bot mentions, the mention goes completely undetected.

Root cause

The data flow has three independent gaps that combine into one failure:

1. app_mention not sent — Slack does not fire app_mention events for bot-originated messages, so isMention is never pre-set by the adapter.
2. parseSlackMessage ignores blocks — Message text is built exclusively from event.text || "". When blocks is the canonical content and event.text is a fallback string (or empty), mentions in rich-text user elements are lost.
3. detectMention checks only message.text — The chat SDK's fallback mention detector scans message.text for @botUserId patterns but never inspects message.raw.blocks.

Relevant code paths:

• @chat-adapter/slack@4.27.0 — parseSlackMessage (line ~2441): const rawText = event.text || ""
• @chat-adapter/slack@4.27.0 — handleMessageEvent (line ~1960): const isMention = event.type === "app_mention"
• chat@4.27.0 — detectMention (line ~3527): only tests message.text against regex patterns
• @chat-adapter/slack@4.27.0 — extractLinks (line ~2358): parses event.blocks but only extracts link elements, not user elements

Slack payload shape for the failure case

{
  "type": "message",
  "subtype": "bot_message",
  "text": "some fallback text without mention",
  "bot_id": "B_OTHER_BOT",
  "blocks": [{
    "type": "rich_text",
    "elements": [{
      "type": "rich_text_section",
      "elements": [
        { "type": "user", "user_id": "U_JUNIOR" },
        { "type": "text", "text": " please look at this" }
      ]
    }]
  }]
}

In this case: event.text has no <@U_JUNIOR>, blocks do, no app_mention fires → mention missed entirely.

Suggested fix

Add a block-level mention scan. Recommended approach:

function slackBlocksMentionUser(event: Record<string, unknown>, botUserId: string): boolean {
  if (!botUserId || !event?.blocks || !Array.isArray(event.blocks)) return false;

  const visit = (node: unknown): boolean => {
    if (!node || typeof node !== "object") return false;
    const n = node as Record<string, unknown>;
    if (n.type === "user" && n.user_id === botUserId) return true;
    if (Array.isArray(n.elements)) return n.elements.some(visit);
    return false;
  };

  return (event.blocks as unknown[]).some(visit);
}

This could live in the adapter's parseSlackMessage (setting isMention on the Message), in Junior's processMessage override, or as a supplemental check alongside detectMention.

Caveats

• Rich-text blocks can be nested (lists, quotes, preformatted). Use recursive traversal.
• Non-rich_text blocks (section, context) may contain mrkdwn text with <@USER_ID> — those should also be scanned.
• Verify skipSelfMention doesn't suppress the mention in edge cases where the bot is both sender and mentionee.

Verification

Gather a real Slack event payload from a bot that @mentions Junior with blocks, and log event.text vs event.blocks to confirm the gap.

Reported by Markus Unterwaditzer. Action taken on behalf of David Cramer.