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+# RFCP Iteration 1.5.1: Fixes & Boundaries
+
+**Date:** January 31, 2025  
+**Type:** Bugfix & Polish  
+**Estimated:** 2-3 hours  
+**Location:** `/opt/rfcp/frontend/` + `/opt/rfcp/backend/`
+
+---
+
+## 🎯 Goal
+
+Fix Fresnel endpoint 500 error, restore coverage boundary visualization, minor polish.
+
+---
+
+## 🐛 Issues to Fix
+
+### 1. Fresnel Endpoint 500 Error
+
+**Symptom:**
+```bash
+curl "/api/terrain/fresnel?tx_lat=48.46&tx_lon=35.05&tx_height=30&rx_lat=48.47&rx_lon=35.06&rx_height=1.5&frequency=1800"
+# Returns: 500 Internal Server Error
+```
+
+**Location:** `backend/app/api/routes/terrain.py`
+
+**Likely cause:** Missing `rx_height` default or async issue in `los_service.check_fresnel_clearance()`
+
+**Fix:**
+```python
+@router.get("/fresnel")
+async def check_fresnel(
+    tx_lat: float,
+    tx_lon: float,
+    tx_height: float,
+    rx_lat: float,
+    rx_lon: float,
+    rx_height: float = 1.5,  # Default receiver height
+    frequency: float = 1800   # Default frequency MHz
+):
+    try:
+        result = await los_service.check_fresnel_clearance(
+            tx_lat, tx_lon, tx_height,
+            rx_lat, rx_lon, rx_height,
+            frequency
+        )
+        return result
+    except Exception as e:
+        raise HTTPException(500, f"Fresnel calculation error: {str(e)}")
+```
+
+**Debug:** Check backend logs for actual error:
+```bash
+journalctl -u rfcp-backend -n 50 | grep -i error
+```
+
+---
+
+### 2. Coverage Boundary Not Showing
+
+**Symptom:** Boundary contour line (-100 dBm) not visible on map after API integration
+
+**Location:** `frontend/src/components/map/CoverageBoundary.tsx`
+
+**Likely cause:** Component expecting old data format, not new API response
+
+**Check:**
+1. Is `CoverageBoundary` still mounted in map?
+2. Does it receive `points` from coverage store?
+3. Is boundary calculation using correct field (`rsrp` vs old field name)?
+
+**Fix approach:**
+```typescript
+// CoverageBoundary.tsx
+import { useCoverageStore } from '../../store/coverage';
+
+export function CoverageBoundary() {
+  const { points, settings } = useCoverageStore();
+  
+  // Generate boundary from API points
+  const boundaryPoints = useMemo(() => {
+    if (!points.length) return [];
+    
+    // Filter points near threshold
+    const threshold = settings.min_signal; // -100 dBm
+    const tolerance = 5; // ±5 dBm
+    
+    return points
+      .filter(p => Math.abs(p.rsrp - threshold) < tolerance)
+      .map(p => [p.lat, p.lon] as [number, number]);
+  }, [points, settings.min_signal]);
+
+  // ... rest of boundary rendering
+}
+```
+
+**Alternative:** Use convex hull or marching squares for proper contour:
+```typescript
+import { concaveman } from 'concaveman';
+
+const boundaryPolygon = useMemo(() => {
+  const edgePoints = points
+    .filter(p => p.rsrp >= settings.min_signal && p.rsrp < settings.min_signal + 10)
+    .map(p => [p.lon, p.lat]);
+  
+  if (edgePoints.length < 3) return null;
+  
+  return concaveman(edgePoints, 2); // concavity factor
+}, [points, settings.min_signal]);
+```
+
+---
+
+### 3. Minor Polish
+
+**a) Stats panel — show models used:**
+```typescript
+// StatsPanel.tsx
+{lastCalculation && (
+  <div className="models-used">
+    <span className="label">Models:</span>
+    <div className="model-tags">
+      {lastCalculation.models.map(m => (
+        <span key={m} className="model-tag">{m}</span>
+      ))}
+    </div>
+  </div>
+)}
+```
+
+**b) Loading state during long calculations:**
+```typescript
+// Show elapsed time during calculation
+const [elapsed, setElapsed] = useState(0);
+
+useEffect(() => {
+  if (!isCalculating) {
+    setElapsed(0);
+    return;
+  }
+  
+  const start = Date.now();
+  const interval = setInterval(() => {
+    setElapsed(Math.floor((Date.now() - start) / 1000));
+  }, 1000);
+  
+  return () => clearInterval(interval);
+}, [isCalculating]);
+
+// In render:
+{isCalculating && (
+  <div className="calculating-status">
+    Calculating... {elapsed}s
+  </div>
+)}
+```
+
+**c) Error toast for API failures:**
+```typescript
+// In coverage store calculateCoverage()
+catch (error) {
+  const message = error instanceof Error ? error.message : 'Calculation failed';
+  toast.error(message); // If using toast library
+  set({ error: message, isCalculating: false });
+}
+```
+
+---
+
+## ✅ Tasks
+
+- [ ] Fix Fresnel endpoint (backend)
+- [ ] Debug and check logs for actual error
+- [ ] Restore CoverageBoundary with API points
+- [ ] Test boundary renders correctly
+- [ ] Add elapsed time counter during calculation
+- [ ] Add model tags to stats panel
+- [ ] Test all presets still work
+- [ ] Run integration test — should be 21/21
+
+---
+
+## 🧪 Testing
+
+```bash
+# 1. Test Fresnel fix
+curl "https://api.rfcp.eliah.one/api/terrain/fresnel?tx_lat=48.46&tx_lon=35.05&tx_height=30&rx_lat=48.47&rx_lon=35.06&rx_height=1.5&frequency=1800"
+# Should return: {"clearance_percent": ..., "has_adequate_clearance": ...}
+
+# 2. Run integration test
+./rfcp-integration-test.sh
+# Should be 21/21
+
+# 3. Visual test
+# - Calculate coverage
+# - Verify boundary line appears at -100 dBm edge
+# - Verify elapsed time shows during calculation
+```
+
+---
+
+## 📁 Files to Modify
+
+```
+backend/app/
+├── api/routes/terrain.py          # Fresnel fix
+└── services/los_service.py        # Check fresnel method
+
+frontend/src/
+├── components/
+│   ├── map/CoverageBoundary.tsx   # Fix boundary rendering
+│   └── panels/
+│       ├── CoverageStats.tsx      # Add model tags
+│       └── StatsPanel.tsx         # Elapsed time
+└── store/coverage.ts              # Error handling
+```
+
+---
+
+## 📝 Notes
+
+- Boundary can use simple edge detection or proper contour algorithm
+- `concaveman` is lightweight (~2KB) for concave hull
+- Elapsed time helps user know calculation is progressing
+
+---
+
+**Quick iteration — should be fast** 🚀