fix(gateway/slack): ephemeral slash-command ack, private notice delivery, format_message fixes

[kshitijk4poor]

Summary

Fixes #18182 and salvages #9340 — comprehensive Slack ephemeral messaging improvements:

1. Slash commands now show ephemeral acknowledgements (/q, /btw, /stop, /model, etc.) and route command replies ephemerally, matching Discord's behavior.
2. Operational notices (e.g. sethome prompt) can now be delivered privately via chat_postEphemeral when slack.notice_delivery: private is configured.
3. format_message bug fixes — markdown images no longer produce broken Slack links, and literal asterisks with spaces (a * b * c) are no longer mistakenly italicized.

Changes

Commit 1: fix(gateway/slack): ephemeral ack and routing for slash commands

Fixes #18182 — Two gaps combined to produce the bug:

Gap 1 fix — Immediate ephemeral ack:
handle_hermes_command now passes response_type="ephemeral" and "Running /cmd…" text to ack(). Previously the bare await ack() sent an empty 200 OK, which Slack silently swallowed.

Gap 2 fix — Ephemeral reply routing via response_url:

• _handle_slash_command stashes the Slack response_url from the command payload in _slash_command_contexts (keyed by (channel_id, user_id)) before dispatching.
• send() checks for a pending slash context. When found, POSTs to response_url with replace_original: true to swap the ack with the real reply, keeping it ephemeral.
• Stale contexts garbage-collected on lookup (120s TTL). Non-fatal fallback if POST fails.

Commit 2: feat(gateway): private notice delivery and Slack format_message fixes

Salvaged from PR #9340 by @probepark. Cherry-picked onto current main with original authorship preserved.

File	What
gateway/config.py	_normalize_notice_delivery() + GatewayConfig.get_notice_delivery() with per-platform config bridging
gateway/platforms/base.py	send_private_notice() default implementation (falls through to send())
gateway/platforms/slack.py	send_private_notice() via chat_postEphemeral
gateway/run.py	_deliver_platform_notice() helper replaces direct adapter.send() for the sethome notice, with private→public fallback
gateway/platforms/slack.py	app_mention handler now forwards to _handle_slack_message (safe due to ts-based dedup) instead of no-op
gateway/platforms/slack.py	format_message: negative lookbehind prevents markdown images from becoming broken Slack links; italic regex requires non-whitespace boundaries

Commit 3: chore: add probepark to AUTHOR_MAP

Commit 4: fix(gateway/slack): review fixes — scope ephemeral to commands, user isolation

Self-review caught and fixed:

1. Critical — Free-form /hermes <question> routed agent reply ephemeral. The context was stashed unconditionally, so /hermes what's the weather would make the full agent response invisible to the channel. Fix: Only stash when text.startswith("/").

2. Critical — Concurrent users on same channel could steal each other's ephemeral context. _pop_slash_context scanned by channel_id only, so User B's response could consume User A's response_url. Fix: Added a ContextVar (_slash_user_id) that threads the invoking user's ID from _handle_slash_command through to send(). _pop_slash_context now matches the exact (channel_id, user_id) key. ContextVars propagate to child asyncio.Tasks, so the value survives through handle_message → _process_message_background → _send_with_retry → send().

3. Medium — _send_slash_ephemeral skipped truncate_message(). Long responses could silently fail. Fixed.

4. Warning — Bare except Exception: pass in _deliver_platform_notice. Fixed: Logs at debug level.

5. Docs — app_mention dedup dependency on shared event ts. Added comment.

Files changed

File	Lines	What
gateway/platforms/slack.py	+197/-7	Ephemeral ack, response_url routing, ContextVar isolation, send_private_notice, app_mention fix, format_message fixes
gateway/config.py	+25	Notice delivery config normalization and bridging
gateway/platforms/base.py	+20	send_private_notice() abstract with fallback
gateway/run.py	+65/-25	_deliver_platform_notice() helper with debug logging
tests/gateway/test_slack.py	+316	14 ephemeral ack tests (incl. concurrent-user isolation + free-form question regression) + 3 notice/format tests
tests/gateway/test_config.py	+36	Notice delivery config bridging tests
tests/gateway/test_notice_delivery.py	+67	Private notice delivery E2E tests (new file)
scripts/release.py	+2	AUTHOR_MAP entry for probepark

Test plan

• 14 new slash ephemeral tests (concurrent-user isolation, free-form question regression, stash/pop/TTL, response_url routing, fallback)
• 3 notice delivery tests (private, fallback-to-public, default public)
• 3 format_message tests (markdown image, literal asterisks, send_private_notice)
• Full gateway suite: 210 passed (targeted), 4316 passed (full)
• py_compile verified on all modified files