feat: auto-reconcile stale holding mirrors

Closes #94

trex_core/application/ports.py

@@ -8,6 +8,8 @@ from __future__ import annotations
 from typing import Optional, Protocol
 from uuid import UUID
 
+from trex_core.application.auto_reconcile import HoldingsCostBasisEvidence
+
 
 class IntentStore(Protocol):
     """Durable idempotency + audit store for accepted intents (dcy-002 OQ-1).
@@ -64,3 +66,10 @@ class PortfolioHubCostBasisPort(Protocol):
         or any error occurs. The caller must handle None as a graceful-degrade signal.
         """
         ...
+
+    def get_cost_basis_evidence(self, portfolio_id: str) -> HoldingsCostBasisEvidence:
+        """Return strict canonical evidence for automatic holding reconciliation.
+
+        Implementations must not fall back to legacy cost-basis fields.
+        """
+        ...