Replace `assert entry.code_challenge` with a proper if-guard returning a
500 JSON error in the token endpoint, since Python's -O flag strips
asserts and would silently disable PKCE enforcement.
Invalidate the scope cache immediately after Login Flow v2 provisioning
completes, so users no longer hit ProvisioningRequiredError for up to
5 minutes after successfully authenticating.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>