fix(rest): give the bare 501 exits a machine code — NOT_IMPLEMENTED (#4067)

.changeset/cross-object-batch-501-code.md

@@ -0,0 +1,22 @@
+---
+"@objectstack/rest": patch
+---
+
+fix(rest): give the bare 501 error exits a machine `code` (#4067)
+
+Most REST error exits already carry a typed `code` (`VALIDATION_FAILED`,
+`BATCH_NOT_ATOMIC`, `BATCH_TOO_LARGE`, `PERMISSION_DENIED`), and the clone /
+search 501s already answer `{ error, code: 'NOT_IMPLEMENTED' }`. Four 501 exits
+still returned a bare `{ error: '<string>' }` with no code, so a client could
+only key on the prose:
+
+- the cross-object transactional batch route (`POST {basePath}/batch`) when the
+  runtime has no `transaction()` — the last untyped exit on that route, whose
+  siblings (`BATCH_NOT_ATOMIC`, `VALIDATION_FAILED`, the `enforceBatchSize`
+  `BATCH_TOO_LARGE`) were already typed by the #3897 / #3933 / #3939 line;
+- the two `saveMetaItem`-unsupported exits;
+- the UI-view-resolution-unsupported exit.
+
+Each now carries `code: 'NOT_IMPLEMENTED'`, matching the clone / search 501s.
+Additive only — the `error` message is unchanged and no status changes — so
+existing clients are unaffected; new ones can branch on the code.

packages/rest/src/rest-batch-endpoint.test.ts

@@ -109,10 +109,12 @@ describe('POST {basePath}/batch — cross-object transactional batch', () => {
     expect(route!.metadata?.tags).toEqual(expect.arrayContaining(['data', 'batch']));
   });
 
-  it('returns 501 when the runtime has no transactional ObjectQL', async () => {
+  it('returns 501 with a NOT_IMPLEMENTED code when the runtime has no transactional ObjectQL', async () => {
     const { route } = buildServer({}); // no ql provider
     const res = await post(route, { operations: [{ object: 'account', data: {} }] });
     expect(res.statusCode).toBe(501);
+    // Typed like every other 501 (#4067) so clients key on the code, not the prose.
+    expect(res.body.code).toBe('NOT_IMPLEMENTED');
   });
 
   // ── happy path ───────────────────────────────────────────────────────────

packages/rest/src/rest-server.ts

@@ -3334,7 +3334,7 @@ export class RestServer {
                     const environmentId = isScoped ? req.params?.environmentId : undefined;
                     const p = await this.resolveProtocol(environmentId, req);
                     if (!p.saveMetaItem) {
-                        res.status(501).json({ error: 'Save operation not supported by protocol implementation' });
+                        res.status(501).json({ error: 'Save operation not supported by protocol implementation', code: 'NOT_IMPLEMENTED' });
                         return;
                     }
 
@@ -3717,7 +3717,7 @@ export class RestServer {
                     const environmentId = isScoped ? req.params?.environmentId : undefined;
                     const p = await this.resolveProtocol(environmentId, req);
                     if (!p.saveMetaItem) {
-                        res.status(501).json({ error: 'Save operation not supported by protocol implementation' });
+                        res.status(501).json({ error: 'Save operation not supported by protocol implementation', code: 'NOT_IMPLEMENTED' });
                         return;
                     }
 
@@ -3780,7 +3780,7 @@ export class RestServer {
                         } as any);
                         res.json(view);
                     } else {
-                        res.status(501).json({ error: 'UI View resolution not supported by protocol implementation' });
+                        res.status(501).json({ error: 'UI View resolution not supported by protocol implementation', code: 'NOT_IMPLEMENTED' });
                     }
                 } catch (error: any) {
                     logError("[REST] Unhandled error:", error);
@@ -6877,7 +6877,9 @@ export class RestServer {
                     if (this.enforceAuth(req, res, context)) return;
                     const ql = this.objectQLProvider ? await this.objectQLProvider(environmentId) : undefined;
                     if (!ql || typeof ql.transaction !== 'function') {
-                        res.status(501).json({ error: 'Transactional batch not supported by this runtime' });
+                        // Typed like every other 501 on this server (clone/search,
+                        // #4067) so a client can key on the code, not the prose.
+                        res.status(501).json({ error: 'Transactional batch not supported by this runtime', code: 'NOT_IMPLEMENTED' });
                         return;
                     }