What does this PR do?

This fixes #12176 with a narrow bugfix that keeps the affected path aligned with the current Hermes behavior without widening the change surface.

Related Issue

Fixes #12176

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

• skip on_session_finalize when /reset or /new does not have an old session entry to finalize
• add a session-boundary regression test so empty resets stop firing finalize hooks with missing state
• Files: gateway/run.py, tests/gateway/test_session_boundary_hooks.py

How to Test

1. Run uv run --frozen pytest -q -o addopts='' tests/gateway/test_session_boundary_hooks.py -k 'reset_without_old_session_skips_finalize_hook or reset_fires_finalize_hook or finalize_before_reset'
2. Run uv run --frozen ruff check gateway/run.py tests/gateway/test_session_boundary_hooks.py
3. Confirm the affected workflow in /new emits on_session_finalize(session_id=None) when no prior session exists #12176 now follows the expected behavior.

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

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

For New Skills

Screenshots / Logs

Gateway session-boundary regression tests and Ruff checks passed locally on macOS.