Land a composition you authored

It goes through the SAME path a generated composition takes: the real validation gate stack at its live configuration, then namespacing, per-instance CSS scoping, theme-variable injection, asset-slot expansion and hosting. Authored work is not a second-class route.

Timing, theme resolution, text-fit geometry and camera authority belong to the pipeline: author against the values the authoring context returns rather than hard-coding equivalents.

A refusal answers 422 carrying the gate's own verdict, so dry_run: true is free and worth doing first. Expect refusals for a requestAnimationFrame or wall-clock drive (the renderer seeks a paused timeline and never runs one), a <canvas> in the DOM path, an unclosed <template>, no registered timeline, or nodes appended to document.body.

Refuses a scene that is mid-generation rather than racing its write-back (409), and refuses if the scene changed while the composition was in flight (409) — re-read and retry. Free unless the HTML declares generated assets; any cost is reported.

Advisory claims: the response carries claimed_by when another actor holds a live claim on the scene (POST /scenes/{sceneId}/claim). The write is never blocked by a claim.

curl -X PUT "https://example.com/scenes/497f6eca-6276-4993-bfeb-53cbbbba6f08/composition" \  -H "Content-Type: application/json" \  -d '{    "html": "string"  }'

{
  "data": {
    "sceneId": "string",
    "elementId": "string",
    "htmlUrl": "string",
    "previousUrl": "string",
    "applied": true,
    "resolved": true,
    "validation": {
      "property1": null,
      "property2": null
    },
    "mountedAs": {
      "property1": null,
      "property2": null
    },
    "apiCost": 0,
    "claimed_by": {
      "kind": "human",
      "label": "string",
      "since": "string",
      "expires_at": "string",
      "expires_in_s": 0,
      "note": "string"
    }
  }
}

{
  "error": {
    "type": "string",
    "code": "string",
    "message": "string"
  }
}

{
  "error": {
    "type": "string",
    "code": "string",
    "message": "string"
  }
}

{
  "error": {
    "type": "string",
    "code": "string",
    "message": "string"
  }
}

{
  "error": {
    "type": "string",
    "code": "string",
    "message": "string"
  }
}

{
  "error": {
    "type": "string",
    "code": "string",
    "message": "string"
  }
}

{
  "error": {
    "type": "string",
    "code": "string",
    "message": "string"
  }
}

{
  "error": {
    "type": "string",
    "code": "string",
    "message": "string"
  }
}