Preserve native sessions during temporary server outages

src/session-recovery.js

@@ -0,0 +1,14 @@
+/** Classify authoritative rejection separately from temporary server failures.
+ * @param {number} status HTTP response status.
+ */
+export function sessionResponseState(status) {
+  if (status === 401 || status === 403) return 'revoked';
+  return status >= 200 && status < 300 ? 'valid' : 'unavailable';
+}
+
+/** Milliseconds before each retry; attempt zero is the immediate first retry.
+ * @param {number} attempt Zero-based retry index.
+ */
+export function sessionRetryDelay(attempt) {
+  return [0, 3000, 10000, 15000][attempt] ?? 30000;
+}