feat: import Chinese-localized Buzz source snapshot

Signed-off-by: cls_宁波本机 <908705107@qq.com>

mobile/lib/shared/crypto/nip_oa.dart

@@ -0,0 +1,74 @@
+import 'dart:convert';
+import 'dart:typed_data';
+
+import 'package:nostr/nostr.dart' as nostr;
+import 'package:pointycastle/digests/sha256.dart';
+
+/// NIP-OA (Owner Attestation) — verify the `auth` tag on a kind:0 profile
+/// that proves an owner key authorized an agent key.
+///
+/// Tag format: ["auth", "<owner-pubkey-hex>", "<conditions>", "<sig-hex>"]
+/// Preimage:   "nostr:agent-auth:" + agent_pubkey_hex + ":" + conditions
+/// Signature:  BIP-340 Schnorr over SHA256(preimage) by the owner key.
+///
+/// Mirrors `profile_valid_oa_owner_pubkey` in desktop/src-tauri: the tag is
+/// verified against the profile event author, so a forged or stale marker
+/// cannot turn a person into an agent.
+///
+/// Returns the owner pubkey (lowercase hex) for the first valid auth tag,
+/// or null if none verifies.
+String? verifiedOaOwnerPubkey(List<List<String>> tags, String agentPubkey) {
+  final agent = agentPubkey.toLowerCase();
+
+  for (final tag in tags) {
+    if (tag.length != 4 || tag[0] != 'auth') continue;
+
+    final owner = tag[1].toLowerCase();
+    final conditions = tag[2];
+    final sig = tag[3];
+
+    // Self-attestation is meaningless and rejected.
+    if (owner == agent) continue;
+    if (owner.length != 64 || sig.length != 128) continue;
+    if (!_validConditions(conditions)) continue;
+
+    final preimage = utf8.encode('nostr:agent-auth:$agent:$conditions');
+    final digest = SHA256Digest().process(Uint8List.fromList(preimage));
+    final message = digest
+        .map((b) => b.toRadixString(16).padLeft(2, '0'))
+        .join();
+
+    try {
+      if (nostr.Schnorr.verify(
+        publicKey: owner,
+        message: message,
+        signature: sig,
+      )) {
+        return owner;
+      }
+    } catch (_) {
+      // Malformed hex — treat as an invalid tag.
+    }
+  }
+
+  return null;
+}
+
+/// Validate the NIP-OA `conditions` string: empty, or `&`-joined clauses of
+/// `kind=<n>`, `created_at<<n>`, or `created_at><n>` with canonical decimals.
+bool _validConditions(String conditions) {
+  if (conditions.isEmpty) return true;
+  if (conditions.contains(RegExp(r'\s'))) return false;
+
+  for (final clause in conditions.split('&')) {
+    final match = RegExp(
+      r'^(?:kind=|created_at<|created_at>)(0|[1-9][0-9]*)$',
+    ).firstMatch(clause);
+    if (match == null) return false;
+    final value = int.tryParse(match.group(1)!);
+    if (value == null || value > 4294967295) return false;
+    if (clause.startsWith('kind=') && value > 65535) return false;
+  }
+
+  return true;
+}