refactor: move payref archival into set_as_unmined for atomicity

Move the PayRef history archival logic from process_reorg into
CompletedTransactionSql::set_as_unmined so that archive + delete
happens atomically on the same connection. This covers all callers:
both process_reorg (reorg path) and transaction_validation_protocol
(normal validation path).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: SWvheerden

base_layer/wallet/src/transaction_service/storage/sqlite_db.rs

@@ -1486,16 +1486,7 @@ impl TransactionBackend for TransactionServiceSqliteDatabase {
             .filter(completed_transactions::mined_height.ge(reorg_height as i64))
             .load::<i64>(&mut conn)?;
         for tx_id in &tx_ids {
-            // Archive existing payrefs to history before unmining (for reorg tracking).
-            // This is done here rather than in set_as_unmined because set_as_unmined is also
-            // called during normal validation (not just reorgs), and the extra DB operations
-            // would cause lock contention under high load.
-            let tx_id_typed = TxId::from(*tx_id as u64);
-            let existing_payrefs = PayrefSql::find_all_by_tx_id(tx_id_typed, &mut conn)?;
-            for pr in &existing_payrefs {
-                PayrefHistorySql::archive_from_payref(pr, &mut conn)?;
-            }
-            CompletedTransactionSql::set_as_unmined(tx_id_typed, &mut conn)?;
+            CompletedTransactionSql::set_as_unmined((*tx_id as u64).into(), &mut conn)?;
         }
         trace!(
             target: LOG_TARGET,
@@ -2477,6 +2468,13 @@ impl CompletedTransactionSql {
             .execute(conn)
             .num_rows_affected_or_not_found(1)?;
 
+        // Archive existing payrefs to history before deleting, so that
+        // PayRefs from before a reorg can still be looked up.
+        let existing_payrefs = PayrefSql::find_all_by_tx_id(tx_id, conn)?;
+        for pr in &existing_payrefs {
+            PayrefHistorySql::archive_from_payref(pr, conn)?;
+        }
+
         let sent = match existing_tx.sent_output_hashes.as_ref() {
             Some(bytes) => bytes_to_fixedhash_vec(bytes),
             _ => vec![],