What does this PR do?

The TUI spawns duplicate hermes mcp serve child processes per session. Both tui_gateway/server.py (agent creation path) and tui_gateway/slash_worker.py (slash command worker) independently bootstrap MCP tools, each triggering discover_mcp_tools() and spawning its own set of MCP server processes. The slash worker only needs CLI command processing, not MCP-backed tools.

Related Issue

Fixes #15275

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

• tui_gateway/slash_worker.py: Set HERMES_MCP_DISCOVERY=0 unconditionally before importing/constructing HermesCLI, suppressing MCP discovery in the worker process.
• tui_gateway/server.py: When spawning the slash worker subprocess, explicitly set HERMES_MCP_DISCOVERY=0 in the subprocess environment to prevent parent env leakage (e.g., if parent has HERMES_MCP_DISCOVERY=1).
• model_tools.py: Added a guard in the MCP discovery path that checks HERMES_MCP_DISCOVERY env var — skips discover_mcp_tools() when set to "0".

How to Test

1. Run:

   python -m pytest tests/tui_gateway/test_slash_worker_mcp.py -v

2. 6 tests cover:
   • Env var is set before CLI import in worker
   • CLI is not imported at module level (AST check)
   • Guard logic for both suppressed and default paths
   • Subprocess env override at spawn time

Tested on macOS (Python 3.11).

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature (no unrelated commits)
• I've run pytest tests/ -q and all tests pass
• I've added tests for my changes (required for bug fixes, strongly encouraged for features)
• I've tested on my platform: macOS 15 (Darwin 24.6.0)

Documentation & Housekeeping

• I've updated relevant documentation (README, docs/, docstrings) — or N/A
• I've updated cli-config.yaml.example if I added/changed config keys — or N/A
• I've updated CONTRIBUTING.md or AGENTS.md if I changed architecture or workflows — or N/A
• I've considered cross-platform impact (Windows, macOS) per the compatibility guide — or N/A
• I've updated tool descriptions/schemas if I changed tool behavior — or N/A

Screenshots / Logs

python -m pytest tests/tui_gateway/test_slash_worker_mcp.py -v
# 6 tests pass