## Description
Add a clear dashboard view for per-agent token usage so end users can
see Cursor, Claude, Codex, and other detected clients with before/after
token counts, tokens saved, and savings percentages. The stats API now
exposes a stable `agent_usage` object that the dashboard renders near
the top of the session view.
Fixes #
## Type of Change
- [ ] Bug fix (non-breaking change that fixes an issue)
- [x] New feature (non-breaking change that adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update
- [ ] Performance improvement
- [ ] Code refactoring (no functional changes)
## Changes Made
### New Files
**Tests:**
- `tests/test_dashboard_agent_usage.py` — Covers agent classification,
exact per-request aggregation, and aggregate fallback behavior.
### Modified Files
- `headroom/proxy/server.py` — Adds per-agent usage aggregation to
`/stats` with before tokens, after tokens, output tokens, saved tokens,
savings percentage, source, providers, and models.
- `headroom/dashboard/templates/dashboard.html` — Adds a prominent Agent
Usage panel with totals, coverage status, per-agent token-flow bars,
request counts, before/after tokens, saved tokens, and share of savings.
## Testing
- [x] Unit tests pass: `.venv312/bin/pytest
tests/test_dashboard_agent_usage.py`
- [x] Linting passes: `.venv312/bin/ruff check headroom/proxy/server.py
tests/test_dashboard_agent_usage.py`
- [x] Diff whitespace check passes: `git diff --check
origin/main...HEAD`
- [x] Dashboard smoke render: local proxy on `127.0.0.1:8790`, captured
Chrome headless screenshot of `/dashboard`
- [x] New tests added for new functionality
## Checklist
- [x] My code follows the project's style guidelines
- [x] I have performed a self-review of my code
- [x] I have commented my code, particularly in hard-to-understand areas
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing relevant unit tests pass locally with my changes
- [ ] I have made corresponding changes to the documentation
- [ ] I have updated the CHANGELOG.md if applicable
## Additional Notes
The agent usage panel uses exact request-log data when available. If
detailed request logs are empty, it falls back to aggregate
provider/model request counts and labels the coverage as aggregate
fallback so users are not misled.
