Protect the main version inside item scopes

docs/roadmap/remediation.md

@@ -158,7 +158,12 @@ is an unintended restriction beyond the requested feature.
 
 ## 5. Keep default-mode main version ownership inside item scopes — P2
 
-- [ ] Addressed and regression-tested.
+- [x] Addressed and regression-tested.
+
+Completion: default-mode effective protection is translated into the main item's
+local scope, preserving segment intent and effective diagnostic paths. Both
+public entry points reject helper-supplied main declarations and permit unrelated
+version fields. Focused source-version tests and the everyday check passed.
 
 **Owner:** the `mainIsItem` branch of
 [imports.go](../../internal/engine/imports.go), lines 228–235.

facade_source_version_mode_test.go

@@ -101,6 +101,47 @@ func TestFacadeSourceVersionOwnershipAcceptsContextualIndexes(t *testing.T) {
 	}
 }
 
+func TestFacadeItemMainKeepsDefaultVersionOwnership(t *testing.T) {
+	t.Parallel()
+	for _, layered := range []bool{false, true} {
+		for _, protected := range []bool{true, false} {
+			body, helper := "id: main\n", "version: imported-version\n"
+			if !protected {
+				body += "version: main-version\n"
+				helper = "other: {version: permitted}\n"
+			}
+			filesystem := configkit.NewFilesystem("item-main", fstest.MapFS{
+				"main.yml": {Data: []byte(body + "configkit: {imports: [{path: helper.yml}]}\n")}, "helper.yml": {Data: []byte(helper)},
+			})
+			checks := 0
+			definition := configkit.Definition[map[string]any]{Version: &configkit.VersionRule{
+				Path: configkit.Keys("records").Index(0).Key("version"),
+				Check: func(version configkit.Version, _ *configkit.Validation) error {
+					checks++
+					if version.Text != "main-version" {
+						t.Error("helper supplied main version")
+					}
+					return nil
+				},
+			}}
+			var err error
+			if layered {
+				_, err = configkit.LoadLayered[map[string]any](configkit.Input{Source: filesystem.File("main.yml"), Imports: true, Destination: configkit.Keys("records"), PlacementMode: configkit.PlacementModeSequenceItem}, configkit.LayeredOptions[map[string]any]{Definition: definition})
+			} else {
+				_, err = configkit.Load(filesystem.File("main.yml"), configkit.Options[map[string]any]{Definition: definition, Imports: true, Destination: configkit.Keys("records"), PlacementMode: configkit.PlacementModeSequenceItem})
+			}
+			if protected {
+				loadError, ok := err.(*configkit.LoadError)
+				if !ok || len(loadError.Diagnostics()) != 1 || loadError.Diagnostics()[0].Code != configkit.CodeImportVersion || loadError.Diagnostics()[0].Path.String() != "/records/0/version" || checks != 0 {
+					t.Fatalf("layered=%t ownership error = %v, checks=%d", layered, err, checks)
+				}
+			} else if err != nil || checks != 1 {
+				t.Fatalf("unrelated helper version rejected: %v, checks=%d", err, checks)
+			}
+		}
+	}
+}
+
 type sourceVersionModeReader struct {
 	*strings.Reader
 	reads int

internal/engine/imports.go

@@ -230,7 +230,22 @@ func loadImportedWithAccessTrackedAndProcessingPolicy(access *filesystemAccess,
 			return nil, cloneSourceInfos(state.sources), prependDiagnosticPaths(failures, destination.Index(0))
 		}
 		if versionState != nil {
-			if diagnostic := importedVersionClaim(documents, completed, versionState.localRule, 0); diagnostic != nil {
+			protectionRule := versionState.localRule
+			if versionState.mode == sourceVersionModeDefault && protectionRule != nil {
+				prefix := destination.Index(0)
+				relative, inside := relativeHistoryPath(prefix, protectionRule.Path)
+				if !inside || !matchesPathShape(Path{segments: protectionRule.Path.segments[:len(prefix.segments)]}, prefix) {
+					protectionRule = nil
+				} else {
+					scoped := *protectionRule
+					scoped.Path = relative
+					protectionRule = &scoped
+				}
+			}
+			if diagnostic := importedVersionClaim(documents, completed, protectionRule, 0); diagnostic != nil {
+				if rule != nil {
+					diagnostic.Path = rule.Path.clone()
+				}
 				return nil, cloneSourceInfos(state.sources), []Diagnostic{*diagnostic}
 			}
 		}