012 create version: Flow PT REST finding

Q What does creating a Version require, and how are entity links written on create?

Endpoint POST /api/v1/entity/versions ; POST /api/v1/entity/shots ; GET /schema/Version/fields

Docs claim Versions need a project; entity links are written as {type, id}.

Actual

sandbox project id: 1180
Version mandatory fields: ['code']
POST /entity/shots -> 201
shot id: 7444
  201 minimal (project + code): id=26262 rels=['created_by', 'cuts', 'notes', 'open_notes', 'playlists', 'project', 'published_files', 'sg_deliveries', 'tags', 'tasks', 'updated_by', 'user']
  201 with entity link: id=26263 rels=['created_by', 'cuts', 'entity', 'notes', 'open_notes', 'playlists', 'project', 'published_files', 'sg_deliveries', 'tags', 'tasks', 'updated_by', 'user']
  400 entity as bare id (no type): null
  400 no project at all: null

Teaches

Trap. /schema/Version/fields marks only code mandatory, yet a body without project 400s.
An entity link is a hash: "entity": {"type": "Shot", "id": N} creates, "entity": <id> 400s. project takes the identical shape, and reads return both under relationships (probe 004).
The 201 relationships block lists slots that were never set (cuts, playlists, tags), so its keys are not a record of your input. entity appears only when it was written, the one usable confirmation.
Both 400s recorded as null: the probe captured errors[0].detail and these errors have none. The status codes are verified; the message text is <unverified>.

The create contract, every type measured since. Version is not a special case. One row per card, entity_types/<Type>:

type	identity field	flagged `mandatory`	actually required	omitted identity becomes	`unique`
Version	`code`	yes	no	`New Version <id>`	no
Shot	`code`	yes	no	`New Shot <id>`	no
Asset	`code`	yes	no	`New Asset <id>`	no
Sequence	`code`	yes	no	`New Sequence <id>`	no
Task	`content`	yes	no	`New Task <id>`	unmeasured
Playlist	`code`	yes	no	`New Playlist <id>`	no
PublishedFile	`code`	yes	no	`New Published File <id>`	no
Note	`subject`	yes	no	nothing; the row has no title	no
TimeLog	none	only `id`	n/a	n/a; `description` reads `New Time Log`	no
Delivery	`title`	yes	no	`New Delivery <id>`	no

For a project-scoped type, project is the requirement and is flagged mandatory: false; the identity field is flagged mandatory: true and is optional, generated by the server when omitted. {} and the identity field alone both answer 400 API create() missing 'project' attribute: with the body echoed. Nothing is unique on any of them, so keying on code is wrong on every type measured: match on id, and treat a code lookup as a query that can return more than one row.

Omitting the key and sending an empty one are different. {"code": ""} on a create is 400 code 104 Create failed for [Shot]: Cannot set identifier field to empty. (Shot) (entity_types/Shot), and Sequence answers the same message for "" and for null (entity_types/Sequence).

Site-wide types are the boundary, not the rule. Project has no project field at all, and its identity name is the one field flagged both mandatory and unique, so a create there is not idempotent (entity_types/Project).

editable is the same shape of flag and the same shape of wrong. created_at and updated_at are flagged editable: false on Note, Reply, Task and Version, and a create body sets both (probe 070). Neither flag describes the create path; send the body and read the 400.