What does this PR do?

Improves multiline user-message previews in the CLI so submitted prompts are echoed back compactly instead of dumping the entire pasted block into scrollback.

Related Issue

Fixes #TBD

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

• Added preview-formatting helpers in cli.py.
• Added display.user_message_preview defaults in hermes_cli/config.py.
• Set preview defaults to first 2 lines and last 2 lines.
• Added direct preview coverage in tests/cli/test_cli_user_message_preview.py.
• Added config coverage in tests/hermes_cli/test_config.py.

How to Test

1. Run source /Volumes/Shared/turbo/hermes-agent/venv/bin/activate && scripts/run_tests.sh.
2. Run scripts/run_tests.sh tests/cli/test_cli_user_message_preview.py tests/hermes_cli/test_config.py -q.
3. Start hermes, paste a 6+ line block, and verify the echo shows the first 2 lines, an omission marker, and the last 2 lines.

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

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

• Full suite on branch feat/multiline-preview (974953530261): 29 failed, 12918 passed, 38 skipped.
• Clean upstream/main baseline on this machine: 34 failed, 12909 passed, 38 skipped.
• This preview-only split reduced the observed repo-wide failure count by 5 on this machine.