Remote datasets: cap fetch body size

src/app/services/remote-data-errors.test.ts

@@ -32,6 +32,13 @@ describe('remoteFetchErrorMessage', () => {
     expect(msg).not.toMatch(/inline/i);
   });
 
+  test('a too-large body names the size limit and a real fix, not the inline fallback', () => {
+    const msg = remoteFetchErrorMessage(new RemoteFetchError('too-large', 'x'));
+    expect(msg).toMatch(/too large/i);
+    expect(msg).toMatch(/MB/);
+    expect(msg).not.toMatch(/inline/i);
+  });
+
   test('an unknown error still produces a sensible fallback message', () => {
     expect(remoteFetchErrorMessage(new Error('boom'))).toMatch(/couldn't fetch this url/i);
   });

src/app/services/remote-data-errors.ts

@@ -10,7 +10,7 @@
  * create/edit form can fall back to pasting inline; Refresh can only retry.
  */
 
-import { RemoteFetchError } from '../infrastructure/remote-data';
+import { MAX_REMOTE_BYTES, RemoteFetchError } from '../infrastructure/remote-data';
 
 /** Where the error surfaces, which decides the recovery the copy points at. */
 export type FetchRecovery = 'inline' | 'retry';
@@ -45,6 +45,10 @@ export function remoteFetchErrorMessage(err: unknown, recovery: FetchRecovery =
         return `This URL returned no data. Make sure it points directly at a data file. ${next}`;
       case 'timeout':
         return `This URL took too long to respond. ${next}`;
+      case 'too-large':
+        // Neither inline-paste nor a retry helps an oversized file, so this points
+        // at the only real fix instead of the shared next step.
+        return `This file is too large to store as a dataset (over ${Math.round(MAX_REMOTE_BYTES / (1024 * 1024))} MB). Use a smaller file, or pre-aggregate the data before loading it.`;
     }
   }
   return `Couldn't fetch this URL. ${next}`;