[Slack] app_mention events silently dropped by silo — @Plane AI does not respond in Slack

Summary

When a user mentions @Plane in a Slack channel, the app_mention event is delivered to /silo/api/slack/events and silo logs that it received the payload — but silo never dispatches the event internally, so Plane AI never produces a reply.

Environment

• Self-hosted Plane with makeplane/silo-commercial image
• GovSlack (Slack for Government) — Socket Mode integration
• A lightweight Socket Mode adapter forwards all payloads to silo over HTTP, re-signing requests with SLACK_SIGNING_SECRET

Steps to reproduce

1. Configure the Slack app with the app_mention bot event subscription.
2. Mention @Plane in any channel where the bot is present.
3. Observe silo logs.

Expected behavior

Silo dispatches the app_mention event to its internal handler and Plane AI replies in the Slack thread.

Actual behavior

Silo logs [SLACK_EVENTS] Received payload for the app_mention event but never emits the subsequent [SLACK][EVENT] Received webhook event from slack 🐱 --------- [slack-interaction] log line that appears for other event types.

Other event types (link_shared, message.channels, message.im) are received and dispatched correctly.

app_mention events appear to be silently dropped after receipt — no error is logged.

Silo log comparison

link_shared (working):

[SLACK_EVENTS] Received payload
[SLACK][EVENT] Received webhook event from slack 🐱 --------- [slack-interaction]

app_mention (not working):

[SLACK_EVENTS] Received payload
(nothing further)

Questions

1. Does silo's /silo/api/slack/events endpoint handle app_mention events, or does the Plane AI / @Plane mention feature require a different endpoint?
2. Is there additional configuration (environment variables, feature flags, AI provider API keys) required to enable the @Plane AI Slack feature?