fix(tools): add Slack channel ID parsing to send_message target resolution

[HelmholtzW]

What Changed

Added Slack channel ID parsing to _parse_target_ref() in tools/send_message_tool.py.

Why

_parse_target_ref had handlers for Telegram, Discord, Feishu, WeChat, and Matrix — but not Slack. When send_message was called with a Slack channel ID target (e.g. slack:C0ANYSL2GBE), the ID was not recognized as explicit, causing the message to fall through to the home channel instead of being sent to the specified channel.

Slack channel IDs start with uppercase letters indicating their type:

• C = channel
• D = DM
• G = group (private channel)
• B = bot
• U/F/V/W = user/app identifiers

They may also include a thread timestamp after a colon (e.g. C0ANYSL2GBE:1776351448.347679).

Changes

tools/send_message_tool.py

• Added Slack ID regex ^([BCDFGUVW][A-Z0-9]+)(?::(\d+\.\d+))?$ to _parse_target_ref
• Returns (channel_id, thread_ts, True) for recognized Slack IDs
• Positioned before the generic numeric fallback to prevent false matches

tests/tools/test_send_message_tool.py

• Added TestParseTargetRefSlack class with 10 new tests:
  • Valid IDs for all prefixes (C, D, G, B, U, F, V, W)
  • Thread timestamp extraction
  • Platform specificity (Slack IDs not matched on Telegram/Discord)
  • Negative cases (lowercase, invalid prefix, malformed thread)

How to Test

source venv/bin/activate
pytest tests/tools/test_send_message_tool.py::TestParseTargetRefSlack -v

All 19 parse_target tests pass:

pytest tests/tools/test_send_message_tool.py -v -k "parse_target" -o "addopts="

Platforms Tested

• Linux (Python 3.11.15)
• All existing send_message tests continue to pass
• 10 new Slack ID parsing tests pass

[alt-glitch]

Likely duplicate of #15064 — same fix: treat Slack alphanumeric channel IDs (C.../D.../G...) as explicit targets in send_message target parser. Also related to #14146 (Slack thread_ts support).

[teknium1]

Thanks for the focused Slack target-resolution coverage. This is an automated hermes-sweeper review; current main already implements this behavior.

• tools/send_message_tool.py:552-565 parses Slack conversation IDs and channel_id:thread_ts targets before channel-name resolution.
• tests/tools/test_send_message_tool.py:1622-1663 covers C/G/D IDs, thread targets, whitespace, invalid targets, and platform isolation.
• The behavior landed in 802c7acb813b9845cd2b6aefeaf193e7176908f3 and was tightened by 75d3eaa0e4b9c602933b2ad269f0ea0f593b5d2d to avoid treating invalid U/W user/workspace IDs as direct chat.postMessage conversation targets.

The related duplicate note from @alt-glitch is consistent with the implementation now on main.