Viewer: add retrieval observability panels on top of #26 #41
Description
Summary
Build an observability-first extension of the read-only viewer so retrieval quality and cost can be debugged without API spelunking.
Why
Issue #26 defines a read-only viewer. We should make it useful for tuning, not only inspection.
Scope
- Extend Add a read-only web viewer for sessions and traces #26 with search pipeline observability panels:
- stage latency (expand/embed/retrieve/fuse/rerank/filter)
- candidate counts per stage
- rerank delta (before vs after rank movement)
- top explain factors per selected note
- Add side-by-side drill-down flow:
- search index -> timeline -> note details -> trace explain
- Add mobile-first layout checks for the inspection workflow.
Acceptance Criteria
- A developer can identify where recall or latency regresses from a single viewer session.
- Viewer displays search traces and explain details without extra API tooling.
- Workflow is usable on desktop and mobile.