* Recognize native chat sign-in failures across structured agents
* Fix authentication failures and chat sign-in guidance
* Preserve sign-in diagnostics and command retry context
* fix(native-chat): keep visible sign-in guidance and localize startup rows
* fix(native-chat): separate auth diagnostics from retry guidance
* test(native-chat): align startup guidance expectations
* fix(native-chat): start a new agent for the send after it reports not signed in
* fix(native-chat): scope the signed-out check by fence and read without a snapshot
* fix(native-chat): keep a signed-out agent while it owes work, and read only its own rows
* fix(native-chat): keep a signed-out agent that may owe a wake-up turn, and skip the check during a Stop
