fix(aria2): harden per-transfer DNS fallback (issue #35)

src/utils/downloadErrors.ts

@@ -0,0 +1,23 @@
+import type { DownloadErrorKind } from '../bindings/DownloadErrorKind';
+
+/**
+ * Keep the renderer's presentation classification aligned with the native
+ * Aria2 boundary. This is intentionally narrow: only Aria2's resolver error
+ * or its distinctive DNS-server wording receives DNS-specific guidance.
+ */
+export const classifyDownloadError = (message: unknown): DownloadErrorKind | undefined => {
+  if (typeof message !== 'string') return undefined;
+  const lower = message.toLowerCase();
+  if (
+    lower.includes('aria2 error code 19')
+    || (
+      lower.includes('name resolution')
+      && lower.includes('failed')
+      && lower.includes('could not contact dns')
+    )
+    || lower.includes('could not contact dns server')
+  ) {
+    return 'nameResolution';
+  }
+  return undefined;
+};

src/utils/downloads.test.ts

@@ -50,6 +50,16 @@ describe('download persistence progress snapshots', () => {
     expect(persisted.totalIsEstimate).toBe(false);
   });
 
+  it('does not persist live resolver error classification', () => {
+    const sanitized = redactDownloadForPersistence({
+      ...item('failed'),
+      lastErrorKind: 'nameResolution',
+      lastResolverFallback: true,
+    });
+    expect(sanitized.lastErrorKind).toBeUndefined();
+    expect(sanitized.lastResolverFallback).toBeUndefined();
+  });
+
   it.each(['queued', 'staged', 'retrying', 'processing'] as const)(
     'keeps byte counters for %s snapshots',
     (status) => {

src/utils/downloads.ts

@@ -577,5 +577,9 @@ export const redactDownloadForPersistence = (item: DownloadItem): DownloadItem =
   for (const field of DOWNLOAD_SECRET_FIELDS) {
     delete copy[field];
   }
+  // Error classification is derived from the live native state and must not
+  // become a persistence field or influence a new lifecycle after restart.
+  delete copy.lastErrorKind;
+  delete copy.lastResolverFallback;
   return copy;
 };