What does this PR do?

Adds a pre-timeout warning layer to the gateway inactivity timeout mechanism. When the agent has been idle for gateway_timeout_warning seconds (default: 15 min), a single notification is sent to the user. If inactivity continues to gateway_timeout (default: 30 min), the full timeout fires as before.

This gives users a chance to intervene on slow API providers without disabling the safety timeout.

Related Issue

Fixes #6260

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

• hermes_cli/config.py: Added gateway_timeout_warning default (900s) to DEFAULT_CONFIG["agent"]
• gateway/run.py: Bridge gateway_timeout_warning config key → HERMES_AGENT_TIMEOUT_WARNING env var; poll loop sends a single warning notification before escalating to full timeout
• cli-config.yaml.example: Documented gateway_timeout and gateway_timeout_warning under the agent: section
• tests/gateway/test_gateway_inactivity_timeout.py: New test suite covering warning fires once, warning disabled at 0, warning skipped on unlimited timeout, full timeout still fires after warning, env var parsing

How to Test

1. Set gateway_timeout_warning: 900 and gateway_timeout: 1800 in ~/.hermes/config.yaml
2. Trigger an agent run that goes idle for > 15 min — verify a warning message is received
3. Verify the warning fires only once per run
4. Set gateway_timeout_warning: 0 — verify no warning fires
5. Run pytest tests/gateway/test_gateway_inactivity_timeout.py -v

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(gateway): ...)
• 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
• I've tested on my platform: macOS 15

Documentation & Housekeeping

• I've updated relevant documentation (cli-config.yaml.example)
• I've updated cli-config.yaml.example if I added/changed config keys
• I've updated CONTRIBUTING.md or AGENTS.md if I changed architecture or workflows — N/A
• I've considered cross-platform impact — N/A (env var parsing only)
• I've updated tool descriptions/schemas if I changed tool behavior — N/A

Screenshots / Logs

Example warning message:

⚠️ No activity for 15 min. If the agent does not respond soon, it will be timed out in 15 min. You can continue waiting or use /reset.