Integrate source version checks for main inputs

internal/engine/source_version.go

@@ -41,6 +41,21 @@ type sourceVersionProcessingResult struct {
 	diagnostics []Diagnostic
 }
 
+func effectiveSourceVersionRule(local *VersionRule, destination Path, mode sourceVersionMode) *VersionRule {
+	if local == nil {
+		return nil
+	}
+	if mode == sourceVersionModeDefault {
+		return local
+	}
+	effective := *local
+	effective.Path = Path{
+		segments: append(clonePathSegments(destination.segments, len(local.Path.segments)), local.Path.segments...),
+		invalid:  destination.invalid || local.Path.invalid,
+	}
+	return &effective
+}
+
 type sourceVersionPathAbsence uint8
 
 const (