fix(gateway): bypass trigger router for in-thread @mentions + drop dead button code

[AndySakov]

What

Two changes:

1. _maybe_dispatch_slack_trigger bypass. When the channel is bound to a slack_trigger AND the message is a human in-thread reply AND the text contains the bot's @mention, log status=bypassed_in_thread_mention and return False so the normal agent path handles it.
2. Block Kit button code removal. With feedback-intake migrated to plain-text proposals + in-thread @mention filing (hermes-state slack: wire BabyDidier(dev) into the Inverter workspace (ITRY-1288) #12), the generic ^skill:<name>$ Block Kit action handler and the interactive_actions tool surface have no caller. Delete them rather than leaving dead surface.

Net: ~420 deletions.

Why

(1) In a trigger-bound channel like #brix-feedback-sandbox, in-thread @mentions of the bot were being lost. The router's STATUS_SKIPPED_NOT_TOP_LEVEL branch should fall through, but in practice the operator's @bot file 1 command never produced a response. The explicit bypass routes the event around the router so the agent's general response path picks it up.

(2) feedback-intake was the only Block Kit caller. After migrating to the @mention flow (hermes-state #12), nothing dispatches skill:<name> button clicks. Leaving the machinery behind invites future skills to reach for it and re-introduce the fragility (Slack interactivity callback wiring, schema regressions, recursive payload validation).

Behavior matrix

Event in #brix-feedback-sandbox	Before	After
Top-level message (no @mention)	Fires feedback-intake	Unchanged
Top-level message with @bot	Fires feedback-intake	Unchanged
In-thread reply (no @mention)	Skipped, normal flow drops	Unchanged
In-thread @bot reply	Dropped	Reaches agent's general response
Bot's own thread reply	Consumed (loop prevention)	Unchanged

Scope is deliberately thread-only on the bypass. Top-level @mentions in a trigger-bound channel are feedback content; bypassing on top-level @mentions would let any @mention hijack the trigger.

Removed

gateway/platforms/slack.py:

• Generic skill-invoke action registration (^skill:<name>$ regex).
• _handle_skill_invoke_action method.

tools/send_message_tool.py:

• interactive_actions schema property + nested items shape.
• _validate_interactive_actions, _build_slack_blocks_from_interactive_actions.
• _INTERACTIVE_ACTIONS_MAX_COUNT, _SKILL_ACTION_ID_RE, _INTERACTIVE_ACTION_STYLES, _SLACK_TEXT_FALLBACK_MAX_CHARS constants.
• slack_interactive_actions plumbing through _handle_send, _send_to_platform, and _send_slack (the blocks kwarg too).

tests/tools/test_send_message_tool.py:

• TestValidateInteractiveActions, TestBuildSlackBlocksFromInteractiveActions, and the routing/payload tests that exercised slack_interactive_actions / blocks.

Kept

• thread_ts on send_message (cross-platform useful for threading; not button-specific).
• TestSendMessageSchemaShape regression guard (array properties must declare items).
• Slash-confirm Block Kit handlers (hermes_confirm_*); separate flow tied to slash_confirm tool.

Unblocks

feedback-intake skill's new filing flow (hermes-state #12): operators reply @babydidier file <N> in the proposal thread, the agent re-reads the proposal post, parses the numbered [N] anchors, and dispatches inverter-customer-request per index.

How to verify

• python3 -m pytest tests/gateway/test_slack_trigger_dispatch.py -q (10 pass).
• python3 -m pytest tests/tools/test_send_message_tool.py -q (100 pass).
• After deploy: post a top-level message in #brix-feedback-sandbox, wait for the bot's plain-text proposal reply, then reply in-thread with @babydidier file 1. Confirm the bot reads the thread and files proposal 1 to Linear. Log line for the @mention should show status=bypassed_in_thread_mention.

Follow-up

hermes-state cleanup PR: delete the dormant skills/file-cr/.

[lafawnduh1966]

Review Findings

Blocking

None.

Non-blocking

🟡 [1] In-thread mention test still does not prove normal agent dispatch
test_slack_trigger_dispatch.py:175 only calls _maybe_dispatch_slack_trigger() and asserts False. That was already the old result for human thread replies, so it does not prove @bot file 1 reaches handle_message. Add one full _handle_slack_message() test that asserts handle_message is awaited and receives file 1.

[AndySakov]

Addressed in c0bda2ac. New test_in_thread_mention_reaches_agent_dispatch calls _handle_slack_message end-to-end and asserts handle_message is awaited with a MessageEvent carrying "file 1" in .text, reply_to_message_id set to the thread root, no trigger envelope, auto_skill=None. 13/13 trigger-dispatch tests pass.

Kept the existing router-level test_in_thread_mention_bypasses_trigger_router alongside as a unit test pinning the router's internal contract.