diff --git a/litellm/proxy/agent_session_endpoints/ownership.py b/litellm/proxy/agent_session_endpoints/ownership.py
new file mode 100644
index 00000000000..83253099fda
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+++ b/litellm/proxy/agent_session_endpoints/ownership.py
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+"""
+Ownership / access-control helpers for the three-level agent hierarchy
+(Agent -> Session -> Run).
+
+Owner identity for an agent is the SHA-256 hash of the API key that created
+it (``user_api_key_hash``). This matches the existing pattern used by
+``litellm_managedobjecttable`` for containers — but we store the hash on
+the row directly because there are no nested resource lookups here.
+
+Sessions and runs inherit ownership from their parent agent — so if a
+caller can read the parent, they can read the child. Cross-tenant isolation
+is enforced uniformly by ``check_agent_ownership`` which is called from
+every public endpoint before any read or write.
+"""
+
+from typing import Any, Optional
+
+from fastapi import HTTPException
+
+from litellm.proxy._types import LitellmUserRoles, UserAPIKeyAuth
+from litellm.proxy._types import hash_token as _hash_litellm_api_key
+
+
+def caller_api_key_hash(user_api_key_dict: UserAPIKeyAuth) -> str:
+    """Return the SHA-256 hash of the caller's API key.
+
+    ``user_api_key_dict.api_key`` may already be hashed (DB-issued virtual
+    keys store the hash), or it may be a master key in plain form. Either
+    way we hash whatever we get — hashing an already-hashed value gives a
+    deterministic value that can never collide with a real raw key.
+    """
+    api_key = user_api_key_dict.api_key
+    if not api_key:
+        raise HTTPException(status_code=401, detail="Missing API key on auth context")
+    return _hash_litellm_api_key(api_key)
+
+
+def is_proxy_admin(user_api_key_dict: UserAPIKeyAuth) -> bool:
+    """Proxy admins can access any agent / session / run regardless of owner."""
+    role = user_api_key_dict.user_role
+    if role is None:
+        return False
+    return role in {
+        LitellmUserRoles.PROXY_ADMIN,
+        LitellmUserRoles.PROXY_ADMIN_VIEW_ONLY,
+    }
+
+
+def assert_caller_owns_agent(
+    user_api_key_dict: UserAPIKeyAuth,
+    agent_row: Any,
+) -> None:
+    """Raise 404 if the caller is not the agent's owner (and not an admin).
+
+    404 (not 403) on purpose — leaking existence of another tenant's
+    resource is a fingerprinting risk.
+    """
+    if agent_row is None:
+        raise HTTPException(status_code=404, detail="Agent not found")
+    if is_proxy_admin(user_api_key_dict):
+        return
+    expected_hash = caller_api_key_hash(user_api_key_dict)
+    if agent_row.user_api_key_hash != expected_hash:
+        raise HTTPException(status_code=404, detail="Agent not found")
+
+
+def assert_caller_owns_session(
+    user_api_key_dict: UserAPIKeyAuth,
+    session_row: Any,
+) -> None:
+    """Raise 404 if the caller is not the session's owner (and not admin).
+
+    Sessions carry their own ``user_api_key_hash`` so we don't need to load
+    the parent agent to check ownership."""
+    if session_row is None:
+        raise HTTPException(status_code=404, detail="Session not found")
+    if is_proxy_admin(user_api_key_dict):
+        return
+    expected_hash = caller_api_key_hash(user_api_key_dict)
+    if session_row.user_api_key_hash != expected_hash:
+        raise HTTPException(status_code=404, detail="Session not found")
+
+
+def owner_filter_for_caller(
+    user_api_key_dict: UserAPIKeyAuth,
+) -> Optional[dict]:
+    """Build a Prisma ``where`` clause restricting list queries to the
+    caller's own rows.
+
+    Returns ``None`` for proxy admins (no filter) so callers can spread it
+    into an existing where dict only when needed.
+    """
+    if is_proxy_admin(user_api_key_dict):
+        return None
+    return {"user_api_key_hash": caller_api_key_hash(user_api_key_dict)}