[Streams] Add client-side field name validation for wired streams

x-pack/platform/packages/shared/kbn-streams-schema/index.ts

@@ -39,7 +39,9 @@ export {
 export {
   keepFields,
   namespacePrefixes,
+  otelReservedFields,
   isNamespacedEcsField,
+  isOtelReservedField,
   getRegularEcsField,
 } from './src/helpers/namespaced_ecs';
 export { getAdvancedParameters } from './src/helpers/get_advanced_parameters';

x-pack/platform/packages/shared/kbn-streams-schema/src/helpers/namespaced_ecs.ts

@@ -11,6 +11,23 @@ import { KEEP_FIELDS, NAMESPACE_PREFIXES } from '@kbn/streamlang';
 export const keepFields: readonly string[] = KEEP_FIELDS;
 export const namespacePrefixes: readonly string[] = NAMESPACE_PREFIXES;
 
+/**
+ * Field names that are reserved for OTel compatibility mode.
+ * These are either passthrough objects or alias fields that cannot be used as custom field names.
+ * IMPORTANT: This list must match the keys of baseMappings in logs_layer.ts.
+ * A test in logs_layer.test.ts ensures these stay in sync.
+ */
+export const otelReservedFields = [
+  'body',
+  'attributes',
+  'scope',
+  'resource',
+  'span.id',
+  'message',
+  'trace.id',
+  'log.level',
+] as const;
+
 export const aliases: Record<string, string> = {
   trace_id: 'trace.id',
   span_id: 'span.id',
@@ -38,3 +55,11 @@ export function isNamespacedEcsField(field: string): boolean {
     KEEP_FIELDS.includes(field as any)
   );
 }
+
+/**
+ * Checks if a field name is reserved for OTel compatibility mode.
+ * Reserved fields are either passthrough objects or alias fields that cannot be redefined.
+ */
+export function isOtelReservedField(field: string): boolean {
+  return otelReservedFields.includes(field as (typeof otelReservedFields)[number]);
+}

x-pack/platform/plugins/shared/streams/server/lib/streams/component_templates/logs_layer.test.ts

@@ -6,9 +6,18 @@
  */
 
 import type { InheritedFieldDefinition, Streams } from '@kbn/streams-schema';
+import { otelReservedFields } from '@kbn/streams-schema';
 import { addAliasesForNamespacedFields, baseMappings, baseFields } from './logs_layer';
 
 describe('logs_layer', () => {
+  describe('baseMappings and otelReservedFields sync', () => {
+    it('should have baseMappings keys match otelReservedFields', () => {
+      const baseMappingsKeys = Object.keys(baseMappings).sort();
+      const reservedFieldsSorted = [...otelReservedFields].sort();
+
+      expect(baseMappingsKeys).toEqual(reservedFieldsSorted);
+    });
+  });
   describe('addAliasesForNamespacedFields', () => {
     let mockStreamDefinition: Streams.WiredStream.Definition;
     let mockInheritedFields: InheritedFieldDefinition;