Blind Compare anonymized the pane headers, but each pane still created a helper chat session named "[CMP] <real-model>" and GET /api/sessions returned the session's model field. So the sidebar and the session-list API let a user map "Model A" back to its real model before voting, defeating the blind test.
- Frontend (static/js/compare/index.js, panes.js): in blind mode, name helper sessions by their neutral slot ("[CMP] Model A") instead of the model, matching the existing blind pane labels.
- Backend GET /api/sessions (routes/session_routes.py): blank the model field for [CMP]-prefixed helper sessions via a new _public_model helper.
- Backend /api/compare/start (routes/compare_routes.py): name blind sessions by slot and withhold model_left/model_right/mapping from the blind response (revealed at /vote).
- Tests: tests/test_blind_compare_redaction.py.
Fixes#1285.
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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