@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/buildings_service.py

@@ -1,5 +1,6 @@
 import os
 import re
+import asyncio
 import httpx
 import json
 from typing import List, Optional
@@ -90,7 +91,10 @@ class BuildingsService:
     OpenStreetMap buildings via Overpass API with local caching.
     """
 
-    OVERPASS_URL = "https://overpass-api.de/api/interpreter"
+    OVERPASS_URLS = [
+        "https://overpass-api.de/api/interpreter",
+        "https://overpass.kumi.systems/api/interpreter",
+    ]
     DEFAULT_LEVEL_HEIGHT = 3.0  # meters per floor
     DEFAULT_BUILDING_HEIGHT = 9.0  # 3 floors if unknown
 
@@ -152,7 +156,7 @@ class BuildingsService:
                 self._memory_cache[bbox_key] = buildings
                 return buildings
 
-        # Fetch from Overpass API
+        # Fetch from Overpass API with retry
         print(f"[Buildings] Fetching from Overpass API...")
 
         query = f"""
@@ -166,17 +170,26 @@ class BuildingsService:
         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"[Buildings] Overpass API 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"[Buildings] Overpass attempt {attempt + 1}/{max_retries} failed ({url}): {e}")
+                if attempt < max_retries - 1:
+                    wait_time = 2 ** attempt  # 1s, 2s
+                    print(f"[Buildings] Retrying in {wait_time}s...")
+                    await asyncio.sleep(wait_time)
+                else:
+                    print(f"[Buildings] All {max_retries} attempts failed")
+                    return []
 
         buildings = self._parse_overpass_response(data)