StartResult

A union discriminated by status.

status"started"required

"started": the member exists in state starting; its task is queued.

memberMemberRefrequired

The new member: its name is <agent>-<k>.

status"refused"required

"refused": nothing was done; code says why.

codeStartRefusalrequired

Why it was refused.

detailInvalidDefinition

Present exactly when code is invalid_definition: which field, why, and what is allowed.