fix: support Slack thread targets in send_message

[mzkarami]

Summary

• Add support for Slack chat_id:thread_ts targets in send_message
• Preserve the parsed Slack thread timestamp through target parsing and dispatch
• Pass thread_ts to Slack chat.postMessage so explicit sends land in the requested thread
• Add unit coverage for parsing and dispatching Slack thread targets

Problem

send_message documents platform:chat_id:thread_id style targets for threaded delivery, but Slack channel/DM IDs were previously parsed only as bare C..., G..., or D... IDs. A target like:

slack:C0123456789:1778566499.343239

could not preserve the Slack thread timestamp through _parse_target_ref, so _send_to_platform had no thread_id to pass to Slack. That makes explicit Slack thread delivery unreliable and can cause messages intended for a thread to be sent as normal channel messages instead.

Solution

• Extend _SLACK_TARGET_RE to accept an optional Slack thread_ts suffix
• Return the parsed thread timestamp from _parse_target_ref for Slack targets
• Thread the value through _send_to_platform into _send_slack
• Include thread_ts in the Slack Web API payload when present
• Return thread_id in the success result for observability

Tests

• git diff --check
• /home/dev/.hermes/hermes-agent/venv/bin/python -m pytest tests/tools/test_send_message_tool.py -q

Result:

113 passed, 39 warnings

Warnings are dependency deprecation warnings from existing third-party packages.

[alt-glitch]

Duplicate of #16992 (open since 2026-04-28, same fix). Also duplicates #23764, #21486, #18911, #17741 — all addressing the same _parse_target_ref + _send_slack thread_ts gap.

[mzkarami]

Duplicate of #16992 (open since 2026-04-28, same fix)