@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/tests/test_geometry/test_diffraction.py

@@ -0,0 +1,60 @@
+"""
+Unit tests for knife-edge diffraction calculations.
+"""
+
+import sys
+import os
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), '..', '..'))
+
+from app.geometry.diffraction import knife_edge_loss
+
+
+def freq_to_wl(freq_mhz):
+    return 300.0 / freq_mhz
+
+
+class TestKnifeEdgeLoss:
+    def test_no_obstruction_low_loss(self):
+        """Negative h means clearance above LOS — loss should be small."""
+        loss = knife_edge_loss(d1_m=500, d2_m=500, h_m=-10, wavelength_m=freq_to_wl(1800))
+        assert loss >= 0
+        assert loss < 3
+
+    def test_grazing_obstruction(self):
+        """h=0 means exactly at LOS line — ~6 dB loss."""
+        loss = knife_edge_loss(d1_m=500, d2_m=500, h_m=0, wavelength_m=freq_to_wl(1800))
+        assert 5 < loss < 8
+
+    def test_obstruction_increases_loss(self):
+        wl = freq_to_wl(1800)
+        loss_low = knife_edge_loss(d1_m=500, d2_m=500, h_m=1, wavelength_m=wl)
+        loss_high = knife_edge_loss(d1_m=500, d2_m=500, h_m=10, wavelength_m=wl)
+        assert loss_high > loss_low
+
+    def test_higher_freq_more_loss(self):
+        """Higher frequency = shorter wavelength = more diffraction loss."""
+        loss_low_f = knife_edge_loss(d1_m=500, d2_m=500, h_m=5, wavelength_m=freq_to_wl(450))
+        loss_high_f = knife_edge_loss(d1_m=500, d2_m=500, h_m=5, wavelength_m=freq_to_wl(1800))
+        assert loss_high_f > loss_low_f
+
+    def test_zero_distance_safe(self):
+        """Should not crash on zero distances."""
+        loss = knife_edge_loss(d1_m=0, d2_m=500, h_m=5, wavelength_m=freq_to_wl(900))
+        assert loss >= 0
+
+    def test_large_clearance(self):
+        """Very deep clearance (large negative h) should have near-zero loss."""
+        loss = knife_edge_loss(d1_m=500, d2_m=500, h_m=-50, wavelength_m=freq_to_wl(900))
+        assert loss < 1.0
+
+
+if __name__ == "__main__":
+    instance = TestKnifeEdgeLoss()
+    for method_name in [m for m in dir(instance) if m.startswith("test_")]:
+        try:
+            getattr(instance, method_name)()
+            print(f"  PASS  {method_name}")
+        except Exception as e:
+            print(f"  FAIL  {method_name}: {e}")
+    print("\nAll tests completed.")