RetireContextOutcome

What retire hands back. The caller needs BOTH halves to undo it: the read floor hides the
context and the slug moved, so the ref they arrived with no longer names the row (spec §2.4.1).

{
    "context_id": "f31d7249-b7b1-4729-b3a4-ec0ba07b4686",
    "context_ref": "string",
    "name": "string",
    "slug": "string"
}