diff --git a/API.md b/API.md
index 7f4880c..61d9694 100644
--- a/API.md
+++ b/API.md
@@ -268,6 +268,13 @@ curl -s -X POST http://localhost:5603/api/v1/link/budget \
 - `fade_margin_db`
 - `fresnel_clear`
 - `link_viable`
+- `los_clear`
+- `geometric_los`
+- `first_fresnel_clearance_pct`
+- `fresnel_violations_count`
+- `geometric_obstructions_count`
+- `building_obstructions_count`
+- `worst_obstruction`
 
 При `include_vegetation=true` API сэмплит WorldCover вдоль трассы и добавляет
 P.833 vegetation attenuation в `vegetation_db`. Если landcover raster отсутствует,
@@ -275,7 +282,9 @@ P.833 vegetation attenuation в `vegetation_db`. Если landcover raster от
 
 При `include_buildings=true` API также строит terrain surface profile с DEM и
 OSM buildings, считает Fresnel/LOS и добавляет Bullington-style diffraction loss
-в `diffraction_db`. Поле `fresnel_clear` берётся из этого же анализа.
+в `diffraction_db`. Поле `fresnel_clear` берётся из этого же анализа. Диагностические
+поля `geometric_los`, `worst_obstruction` и счётчики obstruction помогают понять,
+почему `link_viable=false`.
 
 Модели `p452` и `itm` пока возвращают `501 Not Implemented`.
 
diff --git a/api/app/models/__pycache__/link.cpython-313.pyc b/api/app/models/__pycache__/link.cpython-313.pyc
index d81f050..ae9ad9f 100644
Binary files a/api/app/models/__pycache__/link.cpython-313.pyc and b/api/app/models/__pycache__/link.cpython-313.pyc differ
diff --git a/api/app/models/link.py b/api/app/models/link.py
index 83a4f4d..7b26428 100644
--- a/api/app/models/link.py
+++ b/api/app/models/link.py
@@ -3,6 +3,7 @@ from typing import Literal
 from pydantic import BaseModel, Field
 
 from app.models.coverage import LinkRx, LinkTx
+from app.models.terrain import Obstruction
 
 
 class LinkBudgetRequest(BaseModel):
@@ -26,3 +27,10 @@ class LinkBudgetResponse(BaseModel):
     fade_margin_db: float
     fresnel_clear: bool
     link_viable: bool
+    los_clear: bool
+    geometric_los: bool
+    first_fresnel_clearance_pct: float
+    fresnel_violations_count: int
+    geometric_obstructions_count: int
+    building_obstructions_count: int
+    worst_obstruction: Obstruction | None
diff --git a/api/app/services/__pycache__/link.cpython-313.pyc b/api/app/services/__pycache__/link.cpython-313.pyc
index 4236a87..7e193b4 100644
Binary files a/api/app/services/__pycache__/link.cpython-313.pyc and b/api/app/services/__pycache__/link.cpython-313.pyc differ
diff --git a/api/app/services/link.py b/api/app/services/link.py
index c89b617..b7edc89 100644
--- a/api/app/services/link.py
+++ b/api/app/services/link.py
@@ -1,10 +1,11 @@
 from sqlalchemy.orm import Session
 
 from app.core.diffraction import deygout
-from app.core.fresnel import los_analysis
+from app.core.fresnel import LosSample, los_analysis
 from app.core.geo import GeoPoint, sample_path
 from app.core.propagation import manual_link_budget
 from app.models.link import LinkBudgetRequest, LinkBudgetResponse
+from app.models.terrain import Obstruction
 from app.services.terrain import surface_profile_from_points
 from app.services.vegetation import vegetation_loss_along
 
@@ -53,4 +54,33 @@ def link_budget(request: LinkBudgetRequest, db: Session | None = None) -> LinkBu
         vegetation_db=vegetation_db,
         fresnel_clear=los_result.los_clear,
     )
-    return LinkBudgetResponse(**budget.__dict__)
+    geometric_obstructions = [
+        sample for sample in los_result.obstructions if sample.clearance_m < 0
+    ]
+    building_obstructions = [
+        sample
+        for sample in geometric_obstructions
+        if sample.obstruction_type == "building"
+    ]
+    return LinkBudgetResponse(
+        **budget.__dict__,
+        los_clear=los_result.los_clear,
+        geometric_los=los_result.geometric_los,
+        first_fresnel_clearance_pct=los_result.first_fresnel_clearance_pct,
+        fresnel_violations_count=len(los_result.obstructions),
+        geometric_obstructions_count=len(geometric_obstructions),
+        building_obstructions_count=len(building_obstructions),
+        worst_obstruction=_convert_obstruction(los_result.worst_sample),
+    )
+
+
+def _convert_obstruction(sample: LosSample | None) -> Obstruction | None:
+    if sample is None:
+        return None
+    return Obstruction(
+        distance_m=sample.distance_m,
+        clearance_m=sample.clearance_m,
+        fresnel_radius_m=sample.fresnel_radius_m,
+        required_clearance_m=sample.required_clearance_m,
+        type=sample.obstruction_type,
+    )
diff --git a/api/tests/test_vegetation_integration.py b/api/tests/test_vegetation_integration.py
index 9ac7729..f326843 100644
--- a/api/tests/test_vegetation_integration.py
+++ b/api/tests/test_vegetation_integration.py
@@ -45,6 +45,8 @@ def test_link_budget_includes_vegetation_loss(monkeypatch) -> None:
     result = link_service.link_budget(request)
 
     assert result.vegetation_db == 5.0
+    assert result.los_clear is result.fresnel_clear
+    assert result.fresnel_violations_count >= 0
     assert isclose(
         result.total_loss_db,
         result.fspl_db + result.diffraction_db + 5.0,
@@ -94,3 +96,8 @@ def test_link_budget_includes_diffraction_loss(monkeypatch) -> None:
     assert result.diffraction_db > 0
     assert isclose(result.total_loss_db, result.fspl_db + result.diffraction_db)
     assert result.fresnel_clear is False
+    assert result.los_clear is False
+    assert result.geometric_los is False
+    assert result.fresnel_violations_count > 0
+    assert result.geometric_obstructions_count > 0
+    assert result.worst_obstruction is not None