fix: address second round of PR #224 review feedback

- Include qualified name in findPublishedRestService NotFound error
- Propagate backend errors in CREATE OR REPLACE REST service lookup
- Distinguish backend errors from not-found in import/export mapping describe and drop

Author: retran

mdl/executor/cmd_export_mappings.go

@@ -84,7 +84,10 @@ func (e *Executor) describeExportMapping(name ast.QualifiedName) error {
 
 	em, err := e.reader.GetExportMappingByQualifiedName(name.Module, name.Name)
 	if err != nil {
-		return mdlerrors.NewNotFoundMsg("export mapping", name.String(), err.Error())
+		return mdlerrors.NewBackend("get export mapping "+name.String(), err)
+	}
+	if em == nil {
+		return mdlerrors.NewNotFound("export mapping", name.String())
 	}
 
 	if em.Documentation != "" {
@@ -363,7 +366,10 @@ func (e *Executor) execDropExportMapping(s *ast.DropExportMappingStmt) error {
 
 	em, err := e.reader.GetExportMappingByQualifiedName(s.Name.Module, s.Name.Name)
 	if err != nil {
-		return mdlerrors.NewNotFoundMsg("export mapping", s.Name.String(), err.Error())
+		return mdlerrors.NewBackend("get export mapping "+s.Name.String(), err)
+	}
+	if em == nil {
+		return mdlerrors.NewNotFound("export mapping", s.Name.String())
 	}
 
 	if err := e.writer.DeleteExportMapping(em.ID); err != nil {

mdl/executor/cmd_import_mappings.go

@@ -84,7 +84,10 @@ func (e *Executor) describeImportMapping(name ast.QualifiedName) error {
 
 	im, err := e.reader.GetImportMappingByQualifiedName(name.Module, name.Name)
 	if err != nil {
-		return mdlerrors.NewNotFoundMsg("import mapping", name.String(), err.Error())
+		return mdlerrors.NewBackend("get import mapping "+name.String(), err)
+	}
+	if im == nil {
+		return mdlerrors.NewNotFound("import mapping", name.String())
 	}
 
 	if im.Documentation != "" {
@@ -377,7 +380,10 @@ func (e *Executor) execDropImportMapping(s *ast.DropImportMappingStmt) error {
 
 	im, err := e.reader.GetImportMappingByQualifiedName(s.Name.Module, s.Name.Name)
 	if err != nil {
-		return mdlerrors.NewNotFoundMsg("import mapping", s.Name.String(), err.Error())
+		return mdlerrors.NewBackend("get import mapping "+s.Name.String(), err)
+	}
+	if im == nil {
+		return mdlerrors.NewNotFound("import mapping", s.Name.String())
 	}
 
 	if err := e.writer.DeleteImportMapping(im.ID); err != nil {

mdl/executor/cmd_published_rest.go

@@ -3,6 +3,7 @@
 package executor
 
 import (
+	"errors"
 	"fmt"
 	"sort"
 	"strings"
@@ -171,7 +172,7 @@ func (e *Executor) findPublishedRestService(moduleName, name string) (*model.Pub
 			return svc, nil
 		}
 	}
-	return nil, mdlerrors.NewNotFoundMsg("published REST service", "", "not found")
+	return nil, mdlerrors.NewNotFound("published REST service", moduleName+"."+name)
 }
 
 // execCreatePublishedRestService creates a new published REST service.
@@ -188,7 +189,12 @@ func (e *Executor) execCreatePublishedRestService(s *ast.CreatePublishedRestServ
 
 	// Handle CREATE OR REPLACE — delete existing if found
 	if s.CreateOrReplace {
-		if existing, _ := e.findPublishedRestService(s.Name.Module, s.Name.Name); existing != nil {
+		existing, findErr := e.findPublishedRestService(s.Name.Module, s.Name.Name)
+		var nfe *mdlerrors.NotFoundError
+		if findErr != nil && !errors.As(findErr, &nfe) {
+			return mdlerrors.NewBackend("find existing service", findErr)
+		}
+		if existing != nil {
 			if err := e.writer.DeletePublishedRestService(existing.ID); err != nil {
 				return mdlerrors.NewBackend("replace existing service", err)
 			}