Frontend: clarify threshold labels (city-wide default vs production per-zone)

frontend/api/coverage-recommendation.ts

@@ -3,10 +3,18 @@ import { neon } from '@neondatabase/serverless'
 
 const PRIMARY_CITY = 'Dar es Salaam'
 
-// City-wide P97 WBGT threshold from 20 years of ERA5-Land data.
-// ONE threshold for everyone (38.8°C). Informal zones are hotter so they
-// exceed it MORE often — Jangwani triggers 83 days/year vs Kinondoni 0.
-// This ensures the most vulnerable workers get paid FIRST and MOST.
+// FALLBACK (THRESHOLD_MODE=global): city-wide P97 WBGT from 20 years of
+// ERA5-Land data. Used only in the default-env fallback pathway.
+//
+// PRODUCTION (THRESHOLD_MODE=zone_specific, shipped April 2026): each zone
+// carries its own P90 alert / P97 payout calibrated from its own 20-year
+// UHI-corrected WBGT distribution. Example range: Jangwani alert 31.79°C /
+// payout 32.54°C (valley); Vingunguti alert 37.74°C / payout 38.64°C (hot
+// informal). Per-zone trigger frequencies normalize to ~10% alert / ~3%
+// payout per year — the actuarial pattern used by ARC, CCRIF, and SEWA.
+//
+// This constant is only read if per-zone thresholds are unavailable.
+// See climate-risk-engine/CLAUDE.md § "Trigger threshold mode".
 const CITY_P97_WBGT = 38.8
 
 // Real population estimates per zone based on Tanzania NBS 2024 census,

frontend/src/pages/Dashboard.tsx

@@ -285,9 +285,9 @@ function StepOutput({
             {consec} of 5
           </span>
           <span style={{ color: '#8d909e' }}>Alert threshold</span>
-          <span style={{ color: '#1b1e2d', fontVariantNumeric: 'tabular-nums' }}>35.1°C (UHI P90)</span>
+          <span style={{ color: '#1b1e2d', fontVariantNumeric: 'tabular-nums' }}>35.1°C (city-wide default)</span>
           <span style={{ color: '#8d909e' }}>Payout threshold</span>
-          <span style={{ color: '#1b1e2d', fontVariantNumeric: 'tabular-nums' }}>38.8°C (UHI P97)</span>
+          <span style={{ color: '#1b1e2d', fontVariantNumeric: 'tabular-nums' }}>38.8°C (city-wide default)</span>
           <span style={{ color: '#8d909e' }}>Status</span>
           <span style={{ color: '#1b1e2d' }}>{status}</span>
           <span style={{ color: '#8d909e' }}>Forecast source</span>