diff --git a/routes/auth_routes.py b/routes/auth_routes.py
index 1992f8c..60021e1 100644
--- a/routes/auth_routes.py
+++ b/routes/auth_routes.py
@@ -340,6 +340,14 @@ def setup_auth_routes(auth_manager: AuthManager) -> APIRouter:
         ok = auth_manager.rename_user(old_username, new_username, user)
         if not ok:
             raise HTTPException(400, "Cannot rename user")
+        # The owner-rename loop above updated ApiToken.owner in the DB, but the
+        # bearer-token cache still maps each token to the OLD owner. Without
+        # refreshing it, the renamed user's API tokens resolve to the old (now
+        # non-existent) owner and stop reaching their data until the cache next
+        # goes dirty. Invalidate it now, like the token CRUD routes do.
+        invalidator = getattr(request.app.state, "invalidate_token_cache", None)
+        if callable(invalidator):
+            invalidator()
         return {"ok": True, "username": new_username, "renamed_self": old_username == user}
 
     @router.post("/signup-toggle", deprecated=True)
diff --git a/tests/test_rename_user_token_cache.py b/tests/test_rename_user_token_cache.py
new file mode 100644
index 0000000..314c775
--- /dev/null
+++ b/tests/test_rename_user_token_cache.py
@@ -0,0 +1,76 @@
+"""Renaming a user must invalidate the bearer-token cache.
+
+rename_user updates ApiToken.owner (and every other owner-scoped row) in the
+DB, but the bearer-token cache in app.py still maps each token to the OLD
+owner. Without invalidating it, the renamed user's API tokens keep resolving
+to the old (now non-existent) owner and can no longer reach their data until
+the cache happens to refresh. The route must invalidate the cache, like the
+token CRUD routes do.
+"""
+import sys
+import types
+from types import SimpleNamespace
+from unittest.mock import MagicMock
+
+import pytest
+
+
+def _route(router, name):
+    for r in router.routes:
+        if getattr(getattr(r, "endpoint", None), "__name__", "") == name:
+            return r.endpoint
+    raise AssertionError(name)
+
+
+@pytest.fixture
+def rename_endpoint(monkeypatch):
+    import routes.auth_routes as ar
+    import core.database as cdb
+
+    # Neutralize the DB owner-rename loop (no real DB needed for this test).
+    monkeypatch.setattr(cdb, "SessionLocal", lambda: MagicMock())
+    monkeypatch.setattr(cdb, "Base", SimpleNamespace(registry=SimpleNamespace(mappers=[])), raising=False)
+    # Neutralize the JSON-prefs rename.
+    pr = types.ModuleType("routes.prefs_routes")
+    pr._load = lambda: {}
+    pr._save = lambda d: None
+    monkeypatch.setitem(sys.modules, "routes.prefs_routes", pr)
+
+    am = MagicMock()
+    am.is_admin.return_value = True
+    # The real _get_current_user closure resolves the admin via the auth
+    # manager (a module-level monkeypatch can't intercept a closure), so drive
+    # it through the manager instead.
+    am.get_username_for_token.return_value = "admin"
+    am.users = {"alice": {}}
+    am.rename_user.return_value = True
+    return _route(ar.setup_auth_routes(am), "rename_user"), am
+
+
+def _request(invalidator):
+    return SimpleNamespace(
+        cookies={"odysseus_session": "t"},
+        app=SimpleNamespace(state=SimpleNamespace(invalidate_token_cache=invalidator)),
+        state=SimpleNamespace(current_user="admin"),
+    )
+
+
+def test_rename_invalidates_token_cache(rename_endpoint):
+    import asyncio
+    endpoint, _am = rename_endpoint
+    called = {"n": 0}
+    req = _request(lambda: called.__setitem__("n", called["n"] + 1))
+    res = asyncio.run(endpoint("alice", SimpleNamespace(username="alice2"), req))
+    assert res["ok"] is True and res["username"] == "alice2"
+    assert called["n"] == 1, "bearer-token cache was not invalidated on rename"
+
+
+def test_no_invalidator_does_not_crash(rename_endpoint):
+    import asyncio
+    endpoint, _am = rename_endpoint
+    # app.state without the hook (older wiring) must not break rename.
+    req = SimpleNamespace(cookies={"odysseus_session": "t"},
+                          app=SimpleNamespace(state=SimpleNamespace()),
+                          state=SimpleNamespace(current_user="admin"))
+    res = asyncio.run(endpoint("alice", SimpleNamespace(username="alice2"), req))
+    assert res["ok"] is True