Project version protections through item placement

internal/engine/destination_integration_test.go

@@ -193,6 +193,43 @@ func TestLayeredMountedVersionProtectionCoversInheritanceAndUpperTiers(t *testin
 	})
 }
 
+func TestLayeredItemVersionProtectionTracksAssignedPeerIndexes(t *testing.T) {
+	t.Parallel()
+
+	definition := Definition[map[string]any]{
+		Version:               &VersionRule{Path: Keys("schema", "version"), Check: func(Version, *Validation) error { return nil }},
+		sequenceRegistrations: []sequenceRegistration{{path: Keys("catalog", "entries"), identityField: "id"}},
+	}
+	item := func(label string, value map[string]any) Input {
+		return Input{Source: Mapping(label, value), Destination: Keys("catalog", "entries"), placementMode: placementModeSequenceItem}
+	}
+	options := func(inputs ...Input) LayeredOptions[map[string]any] {
+		return LayeredOptions[map[string]any]{Definition: definition, SourceVersionMode: sourceVersionModeIfPresent, Underlays: []Underlay{{Inputs: inputs}}}
+	}
+	main := item("main", map[string]any{"id": "main", "schema": map[string]any{"version": "v1"}})
+
+	t.Run("same assigned main path is protected", func(t *testing.T) {
+		_, err := LoadLayered(main, testSecretBinding(), options(item("underlay", map[string]any{"id": "underlay", "schema": nil})))
+		if got := groupedErrorCode(t, err); got != CodeUnderlayVersion {
+			t.Fatalf("protected item claim code = %s, want %s", got, CodeUnderlayVersion)
+		}
+	})
+
+	t.Run("appended peer does not claim main path", func(t *testing.T) {
+		loaded, err := LoadLayered(main, testSecretBinding(), options(
+			item("first", map[string]any{"id": "first", "schema": map[string]any{"other": "value"}}),
+			item("peer", map[string]any{"id": "peer", "schema": nil}),
+		))
+		if err != nil {
+			t.Fatalf("unrelated appended peer rejected: %v", err)
+		}
+		entries := layeredMapValue(t, testLoaded(loaded).Config, "catalog", "entries").([]any)
+		if len(entries) != 1 || entries[0].(map[string]any)["id"] != "main" {
+			t.Fatalf("main item projection = %#v", entries)
+		}
+	})
+}
+
 type destinationDecodeProbe string
 
 var destinationDecodeProbeValues []string