feat: auto-reconcile stale holding mirrors

Closes #94

trex_core/adapters/portfolio/hub_read.py

@@ -16,10 +16,12 @@ signal (REQ-028 AC-2) without callers seeing raw httpx exceptions.
 from __future__ import annotations
 
 import math
+from datetime import UTC, datetime
 from typing import Any, Optional
 
 import httpx
 
+from trex_core.application.auto_reconcile import HoldingsCostBasisEvidence
 from trex_core.application.portfolio import (
     BrokerCredentialPayload,
     PortfolioHubUnavailableError,
@@ -268,6 +270,56 @@ class PortfolioHubReadAdapter:
             return None, "invalid"
         return value, "ok"
 
+    def get_cost_basis_evidence(self, portfolio_id: str) -> HoldingsCostBasisEvidence:
+        """Return only canonical, complete evidence used by auto-reconcile."""
+        url = f"{self._base_url}/v1/portfolios/{portfolio_id}/holdings/cost-basis"
+        try:
+            resp = self._get(url)
+        except httpx.HTTPError as exc:
+            raise PortfolioHubUnavailableError(
+                f"cost_basis network error: {exc.__class__.__name__}"
+            ) from exc
+        if not (200 <= resp.status_code < 300):
+            raise PortfolioHubUnavailableError(
+                f"cost_basis http_status_{resp.status_code}"
+            )
+        try:
+            body = resp.json()
+        except ValueError as exc:
+            raise PortfolioHubUnavailableError("cost_basis invalid_json") from exc
+        if not isinstance(body, dict):
+            raise PortfolioHubUnavailableError("cost_basis invalid_payload")
+
+        response_pid = body.get("portfolio_id")
+        symbol = body.get("symbol")
+        if str(response_pid or "") != portfolio_id or not isinstance(symbol, str) or not symbol:
+            raise PortfolioHubUnavailableError("cost_basis identity_mismatch")
+
+        def _finite_number(name: str, *, positive: bool) -> float:
+            raw = body.get(name)
+            if isinstance(raw, bool):
+                raise PortfolioHubUnavailableError(f"cost_basis invalid_{name}")
+            try:
+                value = float(str(raw))
+            except (TypeError, ValueError) as exc:
+                raise PortfolioHubUnavailableError(f"cost_basis invalid_{name}") from exc
+            if not math.isfinite(value) or (positive and value <= 0) or (not positive and value < 0):
+                raise PortfolioHubUnavailableError(f"cost_basis invalid_{name}")
+            return value
+
+        warning = body.get("data_completeness_warning")
+        if warning is not None and not isinstance(warning, str):
+            raise PortfolioHubUnavailableError("cost_basis invalid_completeness_warning")
+        return HoldingsCostBasisEvidence(
+            portfolio_id=portfolio_id,
+            symbol=symbol,
+            current_quantity=_finite_number("current_quantity", positive=True),
+            cost_basis_per_unit=_finite_number("cost_basis_per_unit", positive=True),
+            total_cost_basis=_finite_number("total_cost_basis", positive=True),
+            observed_at=datetime.now(tz=UTC),
+            data_completeness_warning=warning or None,
+        )
+
     def get_cost_basis_with_diagnostics(
         self,
         portfolio_id: str,