`--status`, `--stop`, `--list` and `--kill-all` emit a schema-versioned
envelope with an `ok` discriminant under `--json`, from one writer and one
failure-payload builder. Human output is unchanged; the JSON path is additive.
The value is in the failure paths. An agent that gets a bare error line on
stderr and an empty stdout cannot tell a crash from a "not running", so every
failure is a document too — including a missing project, which under `--json`
resolves through the throwing resolver rather than the human-shaped nudge.
