fix(slack): honor Agent Sessions status lifecycle

[yeshymanoharan]

What does this PR do?

Fixes Slack's missing working indicator after the Agent Sessions migration. agents.sessions.setStatus accepts lifecycle values—not free text—so the adapter now sends processing for a non-empty working state and active when clearing. A concrete client that falls back to legacy assistant.threads.setStatus still receives its original free text and empty clear.

Slack contract: agents.sessions.setStatus, loading-state guidance, and compatibility bridge.

Related Issue

Fixes #110374

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 🔒 Security fix
• 📝 Documentation update
• ✅ Tests (adding or improving test coverage)
• ♻️ Refactor (no behavior change)
• 🎯 New skill (bundled or hub)

Changes Made

• Translate status values at the selected Slack API boundary.
• Update Agent Sessions expectations to processing / active.
• Add a focused per-client legacy-fallback regression test.

How to Test

1. scripts/run_tests.sh tests/gateway/test_slack.py tests/gateway/test_slack_agent_sessions_status_fallback.py — 216 passed, 1 skipped.
2. scripts/run-in-hermes-env python scripts/check — 12 checks passed; 0 health findings.
3. git diff --check

Checklist

Code

• I've read the Contributing Guide
• My commit message follows Conventional Commits
• I searched existing issues and PRs; this is a current-main, minimal carrier for the existing fix cluster
• My PR contains only changes related to this bug
• I've run the entire test suite
• python scripts/check passes
• I've added tests for my changes
• I've tested on Debian Linux

Documentation & Housekeeping

• Relevant docstrings updated; user documentation N/A
• Config example N/A — no config changes
• CONTRIBUTING.md / AGENTS.md N/A — no workflow changes
• Cross-platform impact considered — API-boundary-only change
• Tool descriptions/schemas N/A

Screenshots / Logs

N/A — verified with mocked Slack clients and the repository test suite.

[yeshymanoharan]

Closing after reviewing the existing issue and active implementation discussion more closely. I will coordinate with the existing fix cluster rather than add another competing carrier.