#7246 keeps the host's last discovered accounts when a source's discovery
fails. Host listings now discover several scopes (the host's own plus each
provider env), so each scope keeps its own last result, keyed by its launch
environment. A provider's failed read keeps that provider's logins; a changed
env or a disabled provider keeps nothing, and the host's failed read keeps
only the host's logins.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>