Docs: the single-part PUT's refusals include the multipart size, content type and open-session answers

ddiff --git a/docs/object-model.md b/docs/object-model.md
iindex f98af9c..cee6c74 100644
---- a/docs/object-model.md
++++ b/docs/object-model.md
@@@ -135,7 +135,7 @@ All routes live under `/api/v2/:app/objects`.
  |---|---|---|
  | POST | `/` | init. `{ kind, visibility (default private), mime_type, size_bytes, filename, content_hash (expected sha256), metadata (≤ 16 KB), user_id, upload_ttl (60-86400 s), multipart, part_size }` returns 201 `{ id, object, upload: { method: 'PUT', url, token, expires_at, max_bytes, content_type, complete_url, multipart_url } }`. `url` is a [presigned PUT URL](#presigned-uploads). With `multipart: true` (required above `MEDIA_OBJECT_MAX_MB`): `method: 'multipart'`, `url: null`, and `upload.multipart` is the new [session](#multipart-uploads). Checks at init: `size_bytes` against `MEDIA_OBJECT_MAX_MB` (single part) or `MEDIA_MULTIPART_MAX_MB` (413), the quota including reservations (413 `media.quota.exceeded`), the public-size invariant (422) and the [content type](#content-types) for the kind (415 `media.object.unsupported_type`) |
  | POST | `/:id/upload-url` | a fresh presigned single-PUT URL for an uploading object (`{ ttl }` 60-86400 s) |
--| PUT | `/:id/content` | the bytes, single part. Auth is the upload token (`?token=` from init, or `X-Upload-Token`) or the usual credential. Streams to disk computing sha256. Refuses more than the declared size or the limit (413), a size mismatch (400) and quota overrun (413). Stored at `OBJECTS_PATH/<app>/<id>` with a verified local location. Mounted ahead of the JSON body parser, so any Content-Type is taken as raw bytes; the Content-Type becomes `mime_type` when init set none. Can be repeated while the object is `uploading` |
++| PUT | `/:id/content` | the bytes, single part. Auth is the upload token (`?token=` from init, or `X-Upload-Token`) or the usual credential. Streams to disk computing sha256. Refuses more than the declared size or the limit (413; an object declared above `MEDIA_OBJECT_MAX_MB` goes multipart), a size mismatch (400), quota overrun (413), a type that does not suit the kind (415) and a PUT while a multipart session is open (409). Stored at `OBJECTS_PATH/<app>/<id>` with a verified local location. Mounted ahead of the JSON body parser, so any Content-Type is taken as raw bytes; the Content-Type becomes `mime_type` when init set none. Can be repeated while the object is `uploading` |
  | POST | `/:id/complete` | checks the expected hash (422 `media.object.hash_mismatch`), the invariant, the quota and the bytes against the type (415 `media.object.content_mismatch`). Sets `ready` and sends the `media.object.uploaded` webhook. Also accepts the upload token |
  | POST | `/:id/multipart` | start a [multipart session](#multipart-uploads) `{ part_size, size_bytes (when init declared none) }` → 201 |
  | GET | `/:id/multipart/:uploadId` | the session: `parts` received (number, size, sha256), `missing`, `received_bytes`, `expires_at` |