fix(data-access): read response regression

In `es:app`, attempting to read an app that doesn't exist results in an
error being thrown. This commit updates `app` to have the same behavior.

src/backend/src/modules/data-access/AppService.js

@@ -51,10 +51,17 @@ export default class AppService extends BaseService {
                 let existing = null;
 
                 if ( object.uid !== undefined || id !== undefined ) {
-                    existing = await this.#read({
-                        uid: object.uid,
-                        id,
-                    });
+                    try {
+                        existing = await this.#read({
+                            uid: object.uid,
+                            id,
+                        });
+                    } catch ( error ) {
+                        // If entity not found, we'll create it
+                        if ( error.fields?.code !== 'entity_not_found' ) {
+                            throw error;
+                        }
+                    }
                 }
 
                 if ( existing ) {
@@ -234,7 +241,9 @@ export default class AppService extends BaseService {
         const rows = await db.read(stmt, whereValues);
 
         if ( rows.length === 0 ) {
-            return undefined;
+            throw APIError.create('entity_not_found', null, {
+                identifier: uid || JSON.stringify(id),
+            });
         }
 
         const row = rows[0];

src/backend/src/modules/data-access/AppService.test.js

@@ -217,13 +217,14 @@ describe('AppService', () => {
             expect(result.name).toBe('test-app');
         });
 
-        it('should return undefined when no app is found', async () => {
+        it('should throw entity_not_found when no app is found', async () => {
             mockDb.read.mockResolvedValue([]);
 
             const crudQ = AppService.IMPLEMENTS['crud-q'];
-            const result = await crudQ.read.call(appService, { uid: 'nonexistent-uid' });
 
-            expect(result).toBeUndefined();
+            await expect(crudQ.read.call(appService, { uid: 'nonexistent-uid' })).rejects.toMatchObject({
+                fields: { code: 'entity_not_found' },
+            });
         });
 
         it('should throw an error when neither uid nor id is provided', async () => {
@@ -1257,10 +1258,7 @@ describe('AppService', () => {
         it('should call create when entity does not exist', async () => {
             setupContextForWrite(createMockUserActor(1));
 
-            // First read returns empty (entity doesn't exist)
-            mockDb.read
-                .mockResolvedValueOnce([])  // lookup
-                .mockResolvedValue([createMockAppRow()]); // read after create
+            mockDb.read.mockResolvedValue([createMockAppRow()]);
 
             const crudQ = AppService.IMPLEMENTS['crud-q'];
             await crudQ.upsert.call(appService, {