Fence unmanaged lifecycle by snapshot time

Co-authored-by: genichin <4282227+genichin@users.noreply.github.com>

trex_core/application/reconciliation.py

@@ -29,6 +29,7 @@ import hashlib
 import logging
 import math
 import re
+from datetime import UTC, datetime
 from typing import cast
 
 from trex_core.application.alarm_emitter import AlarmEmitter
@@ -407,6 +408,7 @@ def reconcile_core_holdings(
     Returns {key: 'error'|'qty_warning'|'ok'|'unmanaged_position'|
     'managed_non_holding_divergence'} for telemetry.
     """
+    snapshot_observed_at = datetime.now(tz=UTC)
     broker_qty: dict[str, int] = {
         item.symbol: int(item.hldg_qty) for item in broker.get_balance()
     }
@@ -507,6 +509,7 @@ def reconcile_core_holdings(
                             instance_key=instance_key,
                             symbol=sym,
                             quantity=bq,
+                            observed_at=snapshot_observed_at,
                         )
                     except Exception:  # noqa: BLE001
                         _log.exception(
@@ -555,6 +558,7 @@ def reconcile_core_holdings(
             for state in unmanaged_position_store.resolve_absent(
                 instance_key=instance_key,
                 observed_symbols=active_unmanaged_symbols,
+                observed_at=snapshot_observed_at,
             ):
                 _log.info(
                     "unmanaged position resolved: symbol=%s qty=%d instance_key=%s",