Port the mention gating pattern from Telegram, Discord, WhatsApp, and
Matrix adapters to the Slack platform adapter.
- Add _slack_require_mention() with explicit-false parsing and env var
fallback (SLACK_REQUIRE_MENTION)
- Add _slack_free_response_channels() with env var fallback
(SLACK_FREE_RESPONSE_CHANNELS)
- Replace hardcoded mention check with configurable gating logic
- Bridge slack config.yaml settings to env vars
- Bridge free_response_channels through the generic platform bridging loop
- Add 26 tests covering config parsing, env fallback, gating logic
Config usage:
slack:
require_mention: false
free_response_channels:
- "C0AQWDLHY9M"
Default behavior unchanged: channels require @mention (backward compatible).
Based on PR #5885 by dorukardahan, cherry-picked and adapted to current main.
