feat(discord): support threaded free-response channels

[snapss-dev]

Summary

• add discord.free_response_threaded_channels / DISCORD_FREE_RESPONSE_THREADED_CHANNELS
• let selected Discord channels bypass @mention gating while still using auto-created threads for top-level messages
• keep parent-channel matching for replies in threads under those channels

Verification

• /Users/snaps/.hermes/hermes-agent/venv/bin/python -m pytest tests/gateway/test_discord_channel_controls.py -q
• /Users/snaps/.hermes/hermes-agent/venv/bin/python -m py_compile plugins/platforms/discord/adapter.py

[alt-glitch]

Duplicate of #17564 — same feature (Discord threaded free-response channels: bypass @mention gating + auto-thread). #17564 is the earliest open canonical. Large competing cluster also includes #27969. Cross-linking for the maintainer to pick one.

[teknium1]

Thanks for the focused Discord routing implementation. Current main still has the requested gap: ordinary free-response matches at plugins/platforms/discord/adapter.py:6187-6199 feed skip_thread at :6223, so those channels reply inline.

Problems

• The added list is evaluated only in _handle_message, but the earlier on_message filter checks only _discord_free_response_channels() at plugins/platforms/discord/adapter.py:1191-1204. A threaded-free message that mentions a human but not Hermes is dropped before this PR's new predicate runs. The added tests call _handle_message directly, so they do not cover that callback path.
• The new runtime/config surface is not reflected in the existing Discord defaults and documentation (hermes_cli/config.py:2425-2436, website/docs/user-guide/messaging/discord.md:310-385) or the environment isolation/blocklist paths (tests/conftest.py:319-321, tools/environments/local.py:214-216).

Suggested changes

• Share the threaded-free matching logic with the callback's free-response exception and add an event-level regression test for the human-mention path.
• Complete the config/docs/environment-isolation wiring. The member duplicate note identifies canonical open PR feat(discord): add threaded free-response channels #17564, whose current diff already includes those omitted wiring surfaces.

Automated hermes-sweeper review.