feat: show zone resolver diagnostics

tests/test_zone_view.py

@@ -91,6 +91,9 @@ def test_resolver_assigns_seed_nodes_and_boundary_edges() -> None:
     assert resolution.boundary_edges[0].edge_id == "edge.prod-test"
     assert resolution.boundary_edges[0].source_zone_id == "prod"
     assert resolution.boundary_edges[0].target_zone_id == "test"
+    assert "ZONE_EDGE_CROSSES_ZONE_BOUNDARY" in {
+        diagnostic.code for diagnostic in resolution.diagnostics
+    }
 
 
 def test_resolver_attracts_nodes_by_edge_type_direction_and_depth() -> None:
@@ -128,6 +131,9 @@ def test_resolver_attracts_nodes_by_edge_type_direction_and_depth() -> None:
     assert "far" not in resolution.node_assignments
     assert resolution.zone_by_id("prod").internal_edge_ids == ("edge.seed-near",)
     assert resolution.zone_by_id("prod").boundary_edge_ids == ("edge.near-far",)
+    assert "ZONE_ATTRACTION_DEPTH_LIMIT_REACHED" in {
+        diagnostic.code for diagnostic in resolution.diagnostics
+    }
 
 
 def test_resolver_keeps_seed_membership_over_attraction() -> None:
@@ -229,3 +235,19 @@ def test_resolver_serializes_resolution() -> None:
     assert serialized["zones"][0]["id"] == "prod"
     assert serialized["node_assignments"]["svc"]["zone_id"] == "prod"
     assert serialized["node_assignments"]["svc"]["reason"] == "seed"
+
+
+def test_resolver_reports_empty_zone_seed_set() -> None:
+    resolution = resolve_zones(
+        nodes=[_node("svc", deploymentEnvironment="dev")],
+        edges=[],
+        zone_definitions=[
+            {
+                "id": "prod",
+                "membership": {"field": "deploymentEnvironment", "op": "equals", "value": "prod"},
+            }
+        ],
+    )
+
+    assert resolution.zone_by_id("prod").node_ids == ()
+    assert "ZONE_EMPTY_SEED_SET" in {diagnostic.code for diagnostic in resolution.diagnostics}