feat(slack): support !cmd as alternate prefix for slash commands in threads

[teknium1]

Summary

Slack commands now work inside threads via a leading ! prefix (!queue, !stop, !model gpt-5.4, …) — the slash form still works everywhere else.

Slack itself blocks native slash commands inside thread replies ("/queue is not supported in threads. Sorry!") and there is no app-side setting to re-enable them. This PR adds an alternate prefix the platform won't intercept.

Changes

• gateway/platforms/slack.py (+20): in _handle_slack_message, right after reading event.get("text"), rewrite a leading ! to / when the first token resolves via is_gateway_known_command(). Downstream pipeline (MessageType.COMMAND tagging, gateway dispatcher, thread reply routing) is unchanged.
• tests/gateway/test_slack.py (+87): 6 tests — rewrite, args preservation, thread routing (thread_id preserved on the source), casual-message passthrough (!nice work is not rewritten), @suffix matches get_command() stripping, plain / still works.
• website/docs/user-guide/messaging/slack.md (+16): new subsection under "Slash Commands" documenting the workaround and the platform reason.

Validation

	Result
New tests (TestBangPrefixCommands)	6/6 pass
Slack suites (test_slack.py, test_slack_mention.py, test_slack_approval_buttons.py)	264/264 pass — no regressions

Design notes

• ! is the most common bang-command convention (IRC, Twitch, Discord bots). No collision with Hermes itself.
• Scoped to the Slack adapter only. No other platform has Slack's specific thread-block on slash commands.
• Only the first whitespace-delimited token is checked against the known command list, so casual messages like !nice work pass through to the agent unchanged.
• Reported by Gal Vered — Slack returns "/queue is not supported in threads. Sorry!" when invoking slash commands from a thread reply.

[github-actions]

🔎 Lint report: hermes/hermes-2c15911a vs origin/main

ruff

Total: 0 on HEAD, 0 on base (➖ 0)

🆕 New issues: none

✅ Fixed issues: none

Unchanged: 0 pre-existing issues carried over.

ty (type checker)

Total: 8299 on HEAD, 8299 on base (➖ 0)

🆕 New issues (3):

Rule	Count
invalid-argument-type	3

First entries

run_agent.py:7402: [invalid-argument-type] invalid-argument-type: Argument to function `build_anthropic_client` is incorrect: Expected `str`, found `str | dict[Unknown, Unknown] | Any | ... omitted 3 union elements`
run_agent.py:13616: [invalid-argument-type] invalid-argument-type: Argument to function `len` is incorrect: Expected `Sized`, found `(str & ~AlwaysFalsy) | (dict[Unknown, Unknown] & ~AlwaysFalsy) | (Any & ~AlwaysFalsy) | ... omitted 3 union elements`
run_agent.py:13613: [invalid-argument-type] invalid-argument-type: Argument to function `_is_oauth_token` is incorrect: Expected `str`, found `str | dict[Unknown, Unknown] | Any | ... omitted 3 union elements`

✅ Fixed issues (3):

Rule	Count
invalid-argument-type	3

First entries

run_agent.py:13613: [invalid-argument-type] invalid-argument-type: Argument to function `_is_oauth_token` is incorrect: Expected `str`, found `str | dict[Unknown | str, Unknown | str | dict[str, str]] | Any | ... omitted 3 union elements`
run_agent.py:13616: [invalid-argument-type] invalid-argument-type: Argument to function `len` is incorrect: Expected `Sized`, found `(str & ~AlwaysFalsy) | (dict[Unknown | str, Unknown | str | dict[str, str]] & ~AlwaysFalsy) | (Any & ~AlwaysFalsy) | ... omitted 3 union elements`
run_agent.py:7402: [invalid-argument-type] invalid-argument-type: Argument to function `build_anthropic_client` is incorrect: Expected `str`, found `str | dict[Unknown | str, Unknown | str | dict[str, str]] | Any | ... omitted 3 union elements`

Unchanged: 4373 pre-existing issues carried over.

Diagnostics are surfaced as warnings — this check never fails the build.