fix: remove null OpenApiFile on non-spec clients; preserve UnitID on OR MODIFY

- writer_rest.go: drop the else-branch that wrote OpenApiFile=nil for
  manually-created REST clients; Studio Pro omits this field entirely for
  non-spec services, so writing an explicit null can corrupt existing projects
- cmd_rest_clients.go: preserve the existing UnitID on CREATE OR MODIFY so
  any SEND REST REQUEST microflows that reference the service by ID remain
  valid after a re-import; applies to both the spec-driven and manual paths

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: khode-mx

mdl/executor/cmd_rest_clients.go

@@ -316,12 +316,14 @@ func createRestClient(ctx *ExecContext, stmt *ast.CreateRestClientStmt) error {
 		return mdlerrors.NewBackend("build hierarchy", err)
 	}
 
+	var preservedID model.ID
 	for _, existing := range existingServices {
 		existModID := h.FindModuleID(existing.ContainerID)
 		existModName := h.GetModuleName(existModID)
 		if strings.EqualFold(existModName, moduleName) && strings.EqualFold(existing.Name, stmt.Name.Name) {
 			if stmt.CreateOrModify {
-				// Delete existing and recreate
+				// Preserve the existing ID so SEND REST REQUEST references stay valid after replace.
+				preservedID = existing.ID
 				if err := ctx.Backend.DeleteConsumedRestService(existing.ID); err != nil {
 					return mdlerrors.NewBackend("delete existing rest client", err)
 				}
@@ -348,6 +350,10 @@ func createRestClient(ctx *ExecContext, stmt *ast.CreateRestClientStmt) error {
 		Documentation: stmt.Documentation,
 		BaseUrl:       stmt.BaseUrl,
 	}
+	// Preserve the existing ID on OR MODIFY so SEND REST REQUEST references stay valid.
+	if preservedID != "" {
+		svc.ID = preservedID
+	}
 
 	// Authentication — Mendix requires Rest$ConstantValue for BASIC auth credentials
 	// (Rest$StringValue causes InvalidCastException in Studio Pro). When literal
@@ -656,7 +662,8 @@ func createRestClientFromSpec(ctx *ExecContext, stmt *ast.CreateRestClientStmt)
 		svc.Authentication = &model.RestAuthentication{Scheme: stmt.Authentication.Scheme}
 	}
 
-	// Handle OR MODIFY: delete existing if present
+	// Handle OR MODIFY: delete existing if present, preserving UnitID so any
+	// SEND REST REQUEST microflows that reference this service by ID remain valid.
 	existingServices, _ := ctx.Backend.ListConsumedRestServices()
 	h, err := getHierarchy(ctx)
 	if err != nil {
@@ -667,6 +674,8 @@ func createRestClientFromSpec(ctx *ExecContext, stmt *ast.CreateRestClientStmt)
 		existModName := h.GetModuleName(existModID)
 		if strings.EqualFold(existModName, moduleName) && strings.EqualFold(existing.Name, stmt.Name.Name) {
 			if stmt.CreateOrModify {
+				// Reuse the existing ID so microflow references stay valid.
+				svc.ID = existing.ID
 				if err := ctx.Backend.DeleteConsumedRestService(existing.ID); err != nil {
 					return mdlerrors.NewBackend("delete existing rest client", err)
 				}

sdk/mpr/writer_rest.go

@@ -56,16 +56,15 @@ func (w *Writer) serializeConsumedRestService(svc *model.ConsumedRestService) ([
 		"BaseUrlParameter": nil,
 	}
 
-	// OpenApiFile: present when the service was created from an OpenAPI spec.
+	// OpenApiFile: only present when the service was created from an OpenAPI spec.
 	// Field name and subfield are PascalCase to match Studio Pro serialization.
+	// Do NOT write a null entry for manually-created services — Studio Pro omits this field entirely.
 	if svc.OpenApiContent != "" {
 		doc["OpenApiFile"] = bson.M{
 			"$ID":     idToBsonBinary(generateUUID()),
 			"$Type":   "Rest$OpenApiFile",
 			"Content": svc.OpenApiContent,
 		}
-	} else {
-		doc["OpenApiFile"] = nil
 	}
 
 	// BaseUrl as Rest$ValueTemplate