fix(sync): widen transient-error detection and lengthen retry backoff

Android UnknownHostException after Doze-mode resume produced a raw
"Unable to resolve host" snackbar because the post-retry error message
didn't match isRetryableUploadError's patterns, so it skipped the
NetworkUnavailableSPError wrap. Bump the native HTTP retry backoff from
1s/2s to 1.5s/3s (~4.5s budget) to better tolerate post-Doze DNS
staleness, and add the Android phrasing to both transient-error checks
so the error now surfaces as the translated network-warning snackbar.

packages/sync-providers/src/http/native-http-retry.ts

@@ -6,9 +6,14 @@ import { NOOP_SYNC_LOGGER, toSyncLogError, type SyncLogger } from '@sp/sync-core
  * Retries are safe for Dropbox uploads: conditional writes (mode: 'update' with revToMatch
  * or mode: 'add') ensure duplicates fail with UploadRevToMatchMismatchAPIError.
  * Retries are safe for SuperSync: the server uses idempotent operations.
+ *
+ * Budget: 2 retries with 1.5s/3s linear backoff (~4.5s total). The earlier
+ * 1s/2s backoff (~3s) was sometimes too short to recover from Android Doze
+ * DNS staleness after a long background period.
  * @see https://developer.apple.com/library/archive/qa/qa1941/_index.html
  */
 const MAX_RETRIES = 2;
+const RETRY_BACKOFF_MS = 1500;
 
 const DEFAULT_CONNECT_TIMEOUT_MS = 30_000;
 const DEFAULT_READ_TIMEOUT_MS = 120_000;
@@ -85,7 +90,7 @@ export const executeNativeRequestWithRetry = async (
       });
     } catch (retryErr) {
       if (attempt < maxRetries && isTransientNetworkError(retryErr)) {
-        const delayMs = 1000 * (attempt + 1);
+        const delayMs = RETRY_BACKOFF_MS * (attempt + 1);
         // toSyncLogError drops .code on Error instances, so we read it directly
         // off the raw error to preserve platform-specific transient codes
         // (NSURLErrorDomain, SocketTimeoutException, …) in the retry log.
@@ -159,6 +164,11 @@ export const isTransientNetworkError = (e: unknown): boolean => {
     message.includes('cannot find host') ||
     message.includes('hostname could not be found') ||
     message.includes('cannot connect to host') ||
-    message.includes('could not connect to the server')
+    message.includes('could not connect to the server') ||
+    // Android UnknownHostException message ("Unable to resolve host \"…\": No
+    // address associated with hostname"), and the custom WebDavHttp plugin's
+    // wrapped form ("Network error: Unable to resolve host") — defensive
+    // fallback in case the platform-specific code-based check doesn't fire.
+    message.includes('unable to resolve host')
   );
 };

packages/sync-providers/src/http/retryable-upload-error.ts

@@ -20,6 +20,10 @@ const RETRYABLE_UPLOAD_ERROR_PATTERNS: RegExp[] = [
   /\bfailed to fetch\b/,
   /\bnetwork\s*(error|request|failure)?\b/,
   /\bunable to connect\b/,
+  // Android UnknownHostException: "Unable to resolve host \"…\": No address
+  // associated with hostname". Routes the error through NetworkUnavailableSPError
+  // so the user sees the friendly translated warning instead of the raw message.
+  /\bunable to resolve\b/,
   /\btimeout\b/,
   /\beconnrefused\b/,
   /\benotfound\b/,

packages/sync-providers/tests/native-http-retry.spec.ts

@@ -127,6 +127,22 @@ describe('isTransientNetworkError', () => {
       expect(isTransientNetworkError(new Error('cannot connect to host'))).toBe(true);
     });
 
+    it('returns true for Android "Unable to resolve host" message', () => {
+      expect(
+        isTransientNetworkError(
+          new Error(
+            'Unable to resolve host "sync.example.com": No address associated with hostname',
+          ),
+        ),
+      ).toBe(true);
+    });
+
+    it('returns true for custom WebDavHttp "Network error: Unable to resolve host"', () => {
+      expect(
+        isTransientNetworkError(new Error('Network error: Unable to resolve host')),
+      ).toBe(true);
+    });
+
     it('is case-insensitive', () => {
       expect(isTransientNetworkError(new Error('THE NETWORK CONNECTION WAS LOST'))).toBe(
         true,
@@ -223,7 +239,7 @@ describe('executeNativeRequestWithRetry', () => {
 
     expect(result).toBe(successResponse);
     expect(executor).toHaveBeenCalledTimes(2);
-    expect(delays).toEqual([1000]);
+    expect(delays).toEqual([1500]);
   });
 
   it('retries twice and succeeds on third attempt', async () => {
@@ -245,7 +261,7 @@ describe('executeNativeRequestWithRetry', () => {
 
     expect(result).toBe(successResponse);
     expect(executor).toHaveBeenCalledTimes(3);
-    expect(delays).toEqual([1000, 2000]);
+    expect(delays).toEqual([1500, 3000]);
   });
 
   it('throws after exhausting all retries for transient errors', async () => {
@@ -259,7 +275,7 @@ describe('executeNativeRequestWithRetry', () => {
       executeNativeRequestWithRetry(baseConfig, { executor, label: 'Test', delay }),
     ).rejects.toBe(transientError);
     expect(executor).toHaveBeenCalledTimes(3);
-    expect(delays).toEqual([1000, 2000]);
+    expect(delays).toEqual([1500, 3000]);
   });
 
   it('immediately throws non-transient errors without retrying', async () => {
@@ -340,7 +356,7 @@ describe('executeNativeRequestWithRetry', () => {
       url: baseConfig.url,
       attempt: 1,
       maxRetries: 2,
-      delayMs: 1000,
+      delayMs: 1500,
       errorName: 'Error',
       errorCode: 'NSURLErrorDomain',
     });

packages/sync-providers/tests/retryable-upload-error.spec.ts

@@ -89,6 +89,15 @@ describe('isRetryableUploadError', () => {
       expect(isRetryableUploadError('dns resolution failed')).toBe(true);
     });
 
+    it('Android "unable to resolve host" (UnknownHostException)', () => {
+      expect(
+        isRetryableUploadError(
+          'Unable to resolve host "sync.example.com": No address associated with hostname',
+        ),
+      ).toBe(true);
+      expect(isRetryableUploadError('Network error: Unable to resolve host')).toBe(true);
+    });
+
     it('AbortError from Error object', () => {
       const abortError = new Error('The operation was aborted');
       abortError.name = 'AbortError';