Change model source generator to yield data array with layer entries

Change AsyncCatalogModelSourceGenerator from yielding
{ layers: CatalogModelLayer[] } to { data: Array<{ layer: CatalogModelLayer }> }
so that additional contextual data can be attached alongside each layer
in the future.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Fredrik Adelöw <freben@spotify.com>

packages/catalog-model/report-alpha.api.md

@@ -16,7 +16,9 @@ export interface AlphaEntity extends Entity {
 // @alpha
 export type AsyncCatalogModelSourceGenerator = AsyncGenerator<
   {
-    layers: CatalogModelLayer[];
+    data: Array<{
+      layer: CatalogModelLayer;
+    }>;
   },
   void,
   void

packages/catalog-model/src/model/sources/StaticCatalogModelSource.ts

@@ -37,6 +37,6 @@ export class StaticCatalogModelSource implements CatalogModelSource {
   async *read(
     _options?: CatalogModelSourceReadOptions,
   ): AsyncCatalogModelSourceGenerator {
-    yield { layers: this.#layers };
+    yield { data: this.#layers.map(layer => ({ layer })) };
   }
 }

packages/catalog-model/src/model/sources/types.ts

@@ -31,7 +31,7 @@ export interface CatalogModelSourceReadOptions {
  * @alpha
  */
 export type AsyncCatalogModelSourceGenerator = AsyncGenerator<
-  { layers: CatalogModelLayer[] },
+  { data: Array<{ layer: CatalogModelLayer }> },
   void,
   void
 >;
@@ -49,7 +49,7 @@ export type AsyncCatalogModelSourceGenerator = AsyncGenerator<
  * class MyCatalogModelSource implements CatalogModelSource {
  *   async *read() {
  *     yield {
- *       layers: [defaultCatalogEntityModel]
+ *       data: [{ layer: defaultCatalogEntityModel }]
  *     };
  *   }
  * }

plugins/catalog-backend/src/model/ModelHolder.ts

@@ -62,11 +62,11 @@ export class ModelHolder {
           try {
             const result = await iter.next();
             readyCount += 1;
-            const ls = result.value?.layers ?? [];
-            for (const layer of ls) {
-              logger.info(`Loaded catalog model layer: ${layer.layerId}`);
+            const entries = result.value?.data ?? [];
+            for (const entry of entries) {
+              logger.info(`Loaded catalog model layer: ${entry.layer.layerId}`);
             }
-            return ls;
+            return entries.map(entry => entry.layer);
           } finally {
             await iter.return(undefined);
           }