Panel models in the fusion strategy must answer in prose. When the request
carried tools or prior tool_calls/tool messages, agentic panel models kept
emitting tool_calls instead of prose, so extractPanelText() returned empty
and the engine fell into the 503 "All fusion panel models failed" branch.
Panel fan-out now strips tools/tool_choice and flattens tool turns into
assistant prose (instead of dropping them), so panels keep the context but
cannot loop on tools. The judge still receives the unmodified history.
Co-authored-by: warelik <warelik@WARELIK-MB.local>
Co-authored-by: Cursor <cursoragent@cursor.com>
Adds Fusion as a third combo strategy alongside fallback/round-robin. A
fusion combo fans the prompt out to all member models in parallel, then a
configurable judge model synthesizes one final answer from the panel.
- handleFusionChat in open-sse/services/combo.js: quorum-grace collection
caps the straggler penalty, anonymized sources prevent judge brand-bias,
degrades to a direct answer on single survivor and 503 on total failure.
- chat.js dispatches strategy==="fusion" at both combo entry points.
- Combos dashboard: per-combo strategy Select replaces the round-robin
toggle, fusion reveals a judge picker, plus a strategy/capacity explainer.
- tests/unit/combo-fusion.test.js covers fan-out, judge routing/default,
quorum-grace straggler drop, single-survivor and total-failure degradation.
Co-authored-by: Cursor <cursoragent@cursor.com>
