@mytec: feat: Phase 3.0 Architecture Refactor ✅

Major refactoring of RFCP backend:
- Modular propagation models (8 models)
- SharedMemoryManager for terrain data
- ProcessPoolExecutor parallel processing
- WebSocket progress streaming
- Building filtering pipeline (351k → 15k)
- 82 unit tests

Performance: Standard preset 38s → 5s (7.6x speedup)

Known issue: Detailed preset timeout (fix in 3.1.0)

backend/app/services/vegetation_service.py

@@ -6,6 +6,7 @@ Uses ITU-R P.833 approximations for foliage loss.
 """
 
 import os
+import asyncio
 import httpx
 import json
 from typing import List, Tuple, Optional
@@ -81,7 +82,10 @@ class VegetationCache:
 class VegetationService:
     """OSM vegetation for signal attenuation"""
 
-    OVERPASS_URL = "https://overpass-api.de/api/interpreter"
+    OVERPASS_URLS = [
+        "https://overpass-api.de/api/interpreter",
+        "https://overpass.kumi.systems/api/interpreter",
+    ]
 
     # Attenuation dB per 100 meters of vegetation
     ATTENUATION_DB_PER_100M = {
@@ -127,7 +131,7 @@ class VegetationService:
             self._memory_cache[cache_key] = areas
             return areas
 
-        # Fetch from Overpass
+        # Fetch from Overpass with retry
         print(f"[Vegetation] Fetching from Overpass API...")
 
         query = f"""
@@ -143,14 +147,26 @@ class VegetationService:
         out skel qt;
         """
 
-        try:
-            async with httpx.AsyncClient(timeout=60.0) as client:
-                response = await client.post(self.OVERPASS_URL, data={"data": query})
-                response.raise_for_status()
-                data = response.json()
-        except Exception as e:
-            print(f"[Vegetation] Fetch error: {e}")
-            return []
+        data = None
+        max_retries = 3
+        for attempt in range(max_retries):
+            url = self.OVERPASS_URLS[attempt % len(self.OVERPASS_URLS)]
+            try:
+                timeout = 60.0 * (attempt + 1)  # 60s, 120s, 180s
+                async with httpx.AsyncClient(timeout=timeout) as client:
+                    response = await client.post(url, data={"data": query})
+                    response.raise_for_status()
+                    data = response.json()
+                    break
+            except Exception as e:
+                print(f"[Vegetation] Overpass attempt {attempt + 1}/{max_retries} failed ({url}): {e}")
+                if attempt < max_retries - 1:
+                    wait_time = 2 ** attempt  # 1s, 2s
+                    print(f"[Vegetation] Retrying in {wait_time}s...")
+                    await asyncio.sleep(wait_time)
+                else:
+                    print(f"[Vegetation] All {max_retries} attempts failed")
+                    return []
 
         areas = self._parse_response(data)