Harden auth flows and add backend quality gate

backend/app/services/user_cache.py

@@ -89,6 +89,33 @@ def build_jellyseerr_candidate_map(users: List[Dict[str, Any]]) -> Dict[str, int
     return candidate_to_id
 
 
+def find_matching_jellyseerr_user(
+    identifier: str, users: List[Dict[str, Any]]
+) -> Optional[Dict[str, Any]]:
+    target_handles = set(_normalized_handles(identifier))
+    if not target_handles:
+        return None
+    for user in users:
+        if not isinstance(user, dict):
+            continue
+        for key in ("username", "email", "displayName", "name"):
+            if target_handles.intersection(_normalized_handles(user.get(key))):
+                return user
+    return None
+
+
+def extract_jellyseerr_user_email(user: Optional[Dict[str, Any]]) -> Optional[str]:
+    if not isinstance(user, dict):
+        return None
+    value = user.get("email")
+    if not isinstance(value, str):
+        return None
+    candidate = value.strip()
+    if not candidate or "@" not in candidate:
+        return None
+    return candidate
+
+
 def match_jellyseerr_user_id(
     username: str, candidate_map: Dict[str, int]
 ) -> Optional[int]: