Compare-and-set write of one structured program state key.

Latest-wins per key with history: every write appends one versioned row. Omit expectedVersion (or null) to create the key; pass a version to require the current version to match. A mismatch is refused with 409, never merged. A program holds at most 1,000 distinct keys: creating one more is refused with 422 (existing keys keep writing; state is append-only, so keys are never removed). Queue actions append, claim and complete operate on the queue key with an explicit expectedVersion (null creates it). Append requires id, projectId and title; claim and complete require id. claimedBy is the server-derived principal ref. Non-open claims and completion by another principal are refused with typed codes. Every queue mutation appends a history row; queues over 16 KiB are refused. The author is derived from the authenticating principal and is never read from the body.

curl -X POST 'https://app.rensei.ai/api/cli/programs/string/state' \  -H 'Content-Type: application/json' \  -d '{  "key": "string",  "value": null}'

{  "ledgerVersion": "rensei.session-ledger/v1alpha1",  "programVersion": "rensei.session-ledger.program/v1alpha1",  "entry": {    "ledgerVersion": "rensei.session-ledger/v1alpha1",    "programVersion": "rensei.session-ledger.program/v1alpha1",    "programId": "string",    "key": "string",    "version": 1,    "value": null,    "author": {      "kind": "human",      "id": "string"    },    "createdAt": "2019-08-24T14:15:22Z"  },  "created": true}