Track the main version through sequence movement

internal/engine/load_request.go

@@ -95,6 +95,7 @@ func assembleLayeredInput[T any](request loadRequest[T], input assembledInput, a
 	var assembly *assemblyAccumulator
 	mainSourceCount := len(input.sources)
 	mainEvidence := input.versionState.evidenceSince(0)
+	projectVersion := sequenceVersionPath(request.protectionVersion())
 	for index, group := range request.underlays {
 		evidenceStart := len(input.versionState.evidenceSince(0))
 		acquired, diagnostics := acquireUnderlayGroupScopes(group, index+1, request.protectionVersion(), accounting, input.versionState, request.sequencePolicy)
@@ -107,7 +108,13 @@ func assembleLayeredInput[T any](request loadRequest[T], input assembledInput, a
 		if assembly != nil && assembly.current != nil {
 			lower = assembly.current.collectionPolicies
 		}
-		composition, diagnostics := composeUnderlayGroup(acquired, request.protectionVersion(), request.sequencePolicy, lower)
+		protectionRule := request.protectionVersion()
+		if projectVersion {
+			// The main item's final position is known only after tier assembly.
+			// Source-local checks still run during acquisition above.
+			protectionRule = nil
+		}
+		composition, diagnostics := composeUnderlayGroup(acquired, protectionRule, request.sequencePolicy, lower)
 		sourceStart := len(input.sources)
 		input.sources = append(input.sources, acquired.sources...)
 		if len(diagnostics) != 0 {
@@ -160,6 +167,7 @@ func assembleLayeredInput[T any](request loadRequest[T], input assembledInput, a
 		}
 	}
 	if mainComposition != nil {
+		input.versionState.locateMainVersion(mainComposition.root)
 		if assembly == nil {
 			assembly = newAssemblyAccumulator(mainComposition)
 		} else {
@@ -175,6 +183,15 @@ func assembleLayeredInput[T any](request loadRequest[T], input assembledInput, a
 				return input, append(versionDiagnostics, diagnostics...)
 			}
 			projectTierSourceDestinations(input.sources[:mainSourceCount], mainEvidence, operations)
+			input.versionState.projectMainVersion(operations)
+		}
+	}
+	if input.versionState != nil {
+		request.effectiveVersion = input.versionState.effectiveRule
+	}
+	if projectVersion && assembly != nil {
+		if diagnostic := projectedUnderlayVersionDiagnostic(assembly.current.applications, input.sources, request.protectionVersion()); diagnostic != nil {
+			return input, append(versionDiagnostics, *diagnostic)
 		}
 	}
 	if assembly == nil && activeOverlay(request.overlay) {