Snapshot URL datasets locally on add; preview tabular data as a table

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

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+import { describe, expect, test } from 'vitest';
+import { RemoteFetchError } from '../infrastructure/remote-data';
+import { remoteFetchErrorMessage } from './remote-data-errors';
+
+describe('remoteFetchErrorMessage', () => {
+  test('a network failure hedges offline vs cross-origin and offers the inline fallback', () => {
+    const msg = remoteFetchErrorMessage(new RemoteFetchError('network', 'x'));
+    expect(msg).toMatch(/offline/i);
+    expect(msg).toMatch(/cross-origin/i);
+    expect(msg).toMatch(/paste the data inline/i);
+  });
+
+  test('an HTTP 404 explains "not found" without a raw error code', () => {
+    const msg = remoteFetchErrorMessage(new RemoteFetchError('http', 'x', 404));
+    expect(msg).toMatch(/couldn't find/i);
+    expect(msg).not.toMatch(/404/);
+  });
+
+  test('an HTTP 403 explains refused access', () => {
+    expect(remoteFetchErrorMessage(new RemoteFetchError('http', 'x', 403))).toMatch(
+      /refused access/i,
+    );
+  });
+
+  test('an empty body says it returned no data', () => {
+    expect(remoteFetchErrorMessage(new RemoteFetchError('empty', 'x'))).toMatch(/no data/i);
+  });
+
+  test('the retry recovery points at refreshing, not pasting inline', () => {
+    const msg = remoteFetchErrorMessage(new RemoteFetchError('timeout', 'x'), 'retry');
+    expect(msg).toMatch(/refreshing again/i);
+    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

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+/**
+ * Translate a remote-data fetch failure (snapshot model — spec §05 → URL datasets)
+ * into the message shown when adding or refreshing a URL dataset.
+ *
+ * Pure and framework-free so the wording is unit-tested directly — the same split
+ * as `storage-errors`. Follows the recorded error-copy resolution (docs/architecture
+ * /10 → error copy): plain language, name what stopped, and — because every one of
+ * these is user-fixable — point at the next step. No error codes in the user-facing
+ * line (GOV.UK / NN/g #9). The recovery clause adapts to where the error shows: the
+ * create/edit form can fall back to pasting inline; Refresh can only retry.
+ */
+
+import { RemoteFetchError } from '../infrastructure/remote-data';
+
+/** Where the error surfaces, which decides the recovery the copy points at. */
+export type FetchRecovery = 'inline' | 'retry';
+
+function nextStep(recovery: FetchRecovery): string {
+  return recovery === 'inline'
+    ? 'Check the address, or paste the data inline instead.'
+    : 'Check the address and try refreshing again.';
+}
+
+function httpCause(status?: number): string {
+  if (status === 404) return "The server couldn't find anything at this URL.";
+  if (status === 401 || status === 403) return 'The server refused access to this URL.';
+  if (status && status >= 500) return 'The server hit an error serving this URL.';
+  return "The server couldn't return this URL.";
+}
+
+/**
+ * The user-facing message for a fetch failure. `recovery` defaults to `inline`
+ * (the add/edit form); pass `retry` for the Refresh action, which has no inline
+ * fallback.
+ */
+export function remoteFetchErrorMessage(err: unknown, recovery: FetchRecovery = 'inline'): string {
+  const next = nextStep(recovery);
+  if (err instanceof RemoteFetchError) {
+    switch (err.reason) {
+      case 'network':
+        return `Couldn't fetch this URL. Your device may be offline, or the host may block cross-origin requests. ${next}`;
+      case 'http':
+        return `${httpCause(err.status)} ${next}`;
+      case 'empty':
+        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}`;
+    }
+  }
+  return `Couldn't fetch this URL. ${next}`;
+}