fix: copy jinja_options per-instance to prevent shared mutable class default

src/flask/cli.py

@@ -777,7 +777,7 @@ def show_server_banner(debug: bool, app_import_path: str | None) -> None:
         click.echo(f" * Debug mode: {'on' if debug else 'off'}")
 
 
-class CertParamType(click.ParamType[t.Any]):
+class CertParamType(click.ParamType):  # type: ignore[type-arg]
     """Click option type for the ``--cert`` option. Allows either an
     existing file, the string ``'adhoc'``, or an import for a
     :class:`~ssl.SSLContext` object.

src/flask/sansio/app.py

@@ -315,6 +315,9 @@ def __init__(
         #: to load a config from files.
         self.config = self.make_config(instance_relative_config)
 
+        #: Per-instance copy so subclass mutations don't bleed across instances.
+        self.jinja_options = dict(self.__class__.jinja_options)
+
         #: An instance of :attr:`aborter_class` created by
         #: :meth:`make_aborter`. This is called by :func:`flask.abort`
         #: to raise HTTP errors, and can be called directly as well.