feat(CORE-001D2A): tighten quote provider cache normalization

app/services/data_service.py

@@ -53,10 +53,14 @@ class DataService:
         cache_key = f"quote:{normalized_symbol}"
         cached = await self.cache.get_json(cache_key)
         if cached and isinstance(cached, dict):
-            normalized_cached = self._normalize_quote_payload(cached, normalized_symbol)
-            if normalized_cached != cached:
-                await self.cache.set_json(cache_key, normalized_cached)
-            return normalized_cached
+            try:
+                normalized_cached = self._normalize_quote_payload(cached, normalized_symbol)
+            except ValueError:
+                normalized_cached = None
+            if normalized_cached is not None:
+                if normalized_cached != cached:
+                    await self.cache.set_json(cache_key, normalized_cached)
+                return normalized_cached
 
         quote = self._normalize_quote_payload(await self._fetch_quote(normalized_symbol), normalized_symbol)
         await self.cache.set_json(cache_key, quote)
@@ -365,11 +369,43 @@ class DataService:
 
     @staticmethod
     def _normalize_quote_payload(payload: dict[str, Any], symbol: str) -> dict[str, Any]:
-        normalized = dict(payload)
+        """Normalize provider/cache quote payload to explicit contract.
+
+        This is the named boundary adapter between external float-heavy provider
+        payloads and internal quote handling. It ensures:
+
+        - symbol is always present and uppercased
+        - GLD quotes have explicit quote_unit='share' metadata
+        - Non-GLD symbols pass through without auto-assigned units
+
+        Fail-closed: missing/invalid fields are preserved for upstream handling
+        rather than silently defaulted. Type conversion is not performed here.
+
+        Args:
+            payload: Raw quote dict from cache or provider (float-heavy)
+            symbol: Expected symbol (used as fallback if missing from payload)
+
+        Returns:
+            Normalized quote dict with explicit symbol and GLD quote_unit
+        """
+        normalized: dict[str, Any] = dict(payload)
         normalized_symbol = symbol.upper()
-        normalized["symbol"] = str(normalized.get("symbol", normalized_symbol)).upper()
+
+        # Ensure symbol is always present and normalized.
+        # Missing symbol is repaired from the requested key; explicit mismatches are rejected.
+        raw_symbol = normalized.get("symbol", normalized_symbol)
+        normalized_payload_symbol = str(raw_symbol).upper() if raw_symbol is not None else normalized_symbol
+        if raw_symbol is not None and normalized_payload_symbol != normalized_symbol:
+            raise ValueError(
+                f"Quote payload symbol mismatch: expected {normalized_symbol}, got {normalized_payload_symbol}"
+            )
+        normalized["symbol"] = normalized_payload_symbol
+
+        # Add explicit quote_unit for GLD (CORE-002A/B compatibility)
+        # Repair missing or empty unit metadata, but preserve explicit non-empty values
         if normalized["symbol"] == "GLD" and not normalized.get("quote_unit"):
             normalized["quote_unit"] = "share"
+
         return normalized
 
     @staticmethod