T5 · Migrate FMEA relational editor (long pole — last) #185

Summary

Migrate the FMEA Risk Analyzer, including the relational editor (Function → Failure Mode → Effect / Cause / Control) and the editable S/O/D grids from Streamlit to the Next.js app, consuming the API delivered in P3.

The long pole — budget the most time and do it last. 55 of the ~59 session_state sites in the entire codebase live here, driving the st.data_editor grids in apps/fmea/ui/relational.py. Do not start until T1–T4 are all green and the pattern is proven four times over.

Part of P4 · Tool migration. Needs P2 (web foundation) and P3 (API). Strangler fig: Streamlit keeps serving every tool not yet migrated.

Scope

• React view(s) under web/app/app/, calling the P3 endpoints.
• Client-side state only — session state lives in React, there is no server-side session.
• Plotly figures render via the existing framework-agnostic figure builders (react-plotly.js); the chart layer is a host swap, not a rewrite.
• Loading and error states for every API call — this is where API cold start becomes a UX concern rather than an availability one.
• Delete the corresponding Streamlit page in this same issue, once parity is verified.

Constraints

• Session-state sites to re-implement: 55 of ~59 (docs/research/frontend-migration.md §3.3).
• Exact endpoint names bind at execution time against the API actually delivered in P3 — do not assume names from the plan doc.
• Do not touch quality_core or engine logic. Presentation + transport only.
• Parity is measured on numbers, not layout: same input must produce identical results to the Streamlit page it replaces.

Definition of Done

• View live in the web app, wired to the P3 endpoints
• Parity verified against the Streamlit page on the same input — outputs identical
• Loading + error states implemented
• Streamlit page for this tool deleted; nav updated; remaining Streamlit tools still work
• web-gate and gate both green; zero diff to engines
• SME verification
• Definition of Done (📌 Definition of Done — the contract (read before every issue) #43) honored

Refs: epic #107, docs/research/web-platform-migration.md §5.2, docs/research/frontend-migration.md §3.3