Keep a running companion-remote host's crypto identity in sync with the
active profile: subscribe to PlexHome/connection/join streams and rebuild
auth contexts (restarting the broadcast when they change) so a removed
home user or revoked borrowed connection stops controlling the host.
Serialize host start/stop/crypto-rebuild through a lifecycle lock, clean
up peer subscriptions before re-listening, and guard the replaced-client
onDone against clobbering the new client's session. Drop the context.mounted
guards that aborted an app-level host start, fix the DiscoveryView
init-flash/stuck-on-throw, and delete the dead initialize*Crypto helpers.
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