0774 — CLI alert JSON and maintenance durations follow the read contract

Context

Alert latest and history returned the same name/exists/alerts envelope despite the client’s distinct object and array results. Maintenance status serialized UnclaimedFor as nanoseconds while CLI durations otherwise carried units. Scheduler table headings and one registration error used different terminology from the client fields and verbs.

Decision

• Alert latest JSON is the alert object or null; history JSON is the newest-first array or []. Preserve exit 1 for no retained alerts in both commands.
• Maintenance status keeps the worker snapshot’s fields and renders unclaimed_for as a duration string, including “0s”. Use the existing CLI result-document pattern.
• Scheduler tables spell Expression and ConsumerGroup as EXPRESSION and CONSUMER_GROUP; the system error says registered instead of initialized.
• Keep command and flag names, metric series filtering, and worker config reads.

Consequences

Pre-v1 scripts must read alert latest fields directly instead of .alerts[0], and history entries at .[] instead of .alerts[]. Maintenance readers must parse unclaimed_for as a duration instead of dividing nanoseconds. Exit codes still distinguish empty alert reads; the library and database behavior are unchanged.