image: Flow PT field type reference

Data type image, probed on Version.image and Version.filmstrip_image (stock, editable). image_blur_hash is a text field, not this type. On the probed site, across all 114 entity types:

image fields on the type	types
`image` and `filmstrip_image`	39, Version, Shot, Asset, Project and HumanUser among them
`image` alone	10: ClientUser, Department, Episode, Level, PipelineConfiguration, PublishedFileType, Reel, RvLicense, Software, SourceClip
neither	65

No type held an image field under a third name, and every one found reads editable: true.

Read A plain string under attributes, or null. Never under relationships. The value is the only state marker; test for the /images/status/transient/ prefix, never for truthiness.

value	state
`null`	never uploaded
`<site>/images/status/transient/thumbnail_pending.png`	still transcoding
any other string	ready

image / filmstrip_image, 100 Versions on the sample project: {null: 99, url str: 1} each
the value: a presigned S3 URL, 1342-1396 chars
  path   /<40 hex chars>/…        a content hash — the stable half
  query  ['X-Amz-Algorithm', 'X-Amz-Credential', 'X-Amz-Date', 'X-Amz-Expires', 'X-Amz-Signature',
          'X-Amz-Security-Token', 'X-Amz-SignedHeaders', 'response-content-disposition',
          'x-amz-meta-user-id', 'x-amz-meta-user-type']
  X-Amz-Algorithm = AWS4-HMAC-SHA256

read	equal to the previous read?	fetch
`GET /entity/versions/{id}?fields=image`	n/a	`GET` 200 `image/jpeg` 51730 bytes
the same `GET` one second later	no, first differing character at index 353 of 1396	n/a
`POST /entity/versions/_search`	no	n/a
any of them with `HEAD`	n/a	403 `application/xml`
a string held 706 seconds past its `X-Amz-Expires`	n/a	403 `<Code>AccessDenied</Code>`

Re-signed on every read, and the lifetime is X-Amz-Expires seconds from X-Amz-Date: six reads 20 seconds apart each got a fresh 900, one read got 646, so take the number from the URL. Cache the entity id and re-read, never the string. Fetch with GET; the signature covers no other method.

Write Not assignable, on create or on update. null is the only value the field accepts.

sent	code	result
`"https://example.com/thumb.png"`	400	the `expected [Hash, … NilClass]` body below
`"data:image/png;base64,iVBORw0…"` (154 chars)	400	same, `… but got String: "data:image/png;base64,…"`
`"/images/status/transient/x.png"`	400	same
`""`	400	same, `… but got String: ""`
`{"url": "https://example.com/thumb.png"}`	400	`invalid/missing entity hash string 'type'`
`{}`	400	same
`{"type": "Attachment", "id": 0}`	400	`Write access of the 'image' data type … not yet supported`
`{"type": "Attachment", "id": <a real Attachment>}`	400	the same message; an id that resolves changes nothing
`null`	200	cleared
the same string in a `POST /entity/versions` body	400	`API create() Version.image expected [Hash, …`

API update() Version.image expected [Hash, ActiveSupport::HashWithIndifferentAccess, ActionDispatch::Http::Parameters, ActionDispatch::Http::ParamsHashWithIndifferentAccess, NilClass] data type(s) but got String: "https://example.com/thumb.png"
API update() invalid/missing entity hash string 'type': {"url" => "https://example.com/thumb.png"}
 Valid entity types: ["ActionMenuItem", "ApiUser", … 114 of them …, "WorkDayRule"]
API update(): Write access of the 'image' data type (Version.image) not yet supported in API

editable: true in the schema is wrong; the write fails loudly rather than being taken and discarded like cached_display_name (probe 004). The upload dance is the only way in (probe 013). filmstrip_image takes the same three calls, and the field in the path decides the kind, so both report upload_type=Thumbnail:

GET  /entity/versions/{id}/image/_upload?filename=zzprobe.png       -> 200 upload_type=Thumbnail
PUT  {links.upload}  97 bytes                                       -> 200
POST {links.complete_upload} {"upload_info": …, "upload_data": {}}  -> 201
GET  /entity/versions/{id}/filmstrip_image/_upload                  -> 200 upload_type=Thumbnail

Clear

sent	code	`image` after	`filmstrip_image` after
`PUT {"image": null}`	200	`null`	`null`, cleared with it
`PUT {"filmstrip_image": null}`	200	unchanged	`null`
`PUT {"image": ""}`	400	unchanged	unchanged
`DELETE /entity/versions/{id}/image`	404 `Not Found`	unchanged	unchanged

Filter Two relations, and nil is the only legal value:

["image", "definitely_not_an_operator", null] -> 400
 title:  "API read() Version.image's 'image' data type doesn't support
          'definitely_not_an_operator' 'relation'"
 source: {"Version.image": " data type doesn't support … Valid relations: ["is", "is_not"]"}

operator	value	matches	code
`is`	`null`	99 of 100 Versions, no thumbnail	200
`is_not`	`null`	1 of 100, has one, transcoded or not	200
`is`	`""`	`'is' 'relation' expects a nil value for 'image' data type: [""]`	400
`is`	`"https://x/y.png"`	same, `… data type: ["https://x/y.png"]`	400
`contains`	`"thumb"`	`doesn't support 'contains'` … `["is", "is_not"]`	400
`in`	`[null]`	`doesn't support 'in'` … `["is", "is_not"]`	400

_summarize grouping on image is 400 Grouping is not allowed for field Version.image.

on the same Version	`image`	`url` (`sg_uploaded_movie`)
read shape	string	dict (probe 021)
filter	`is`, `is_not`, nil only	no relation at all (probe 021)
transcode state	the path prefix	`sg_uploaded_movie_transcoding_status` (probe 022)

Traps

is_not None matches a row that is still transcoding, so a job that filters and then downloads fetches thumbnail_pending.png. Filter, then check the prefix on each row.
Transcoding took ~38 seconds for a 16x16 97-byte PNG. Poll the field every 5 seconds.
The REST upload never fills image_blur_hash: still null 102 seconds after the thumbnail settled and after a second upload to filmstrip_image. The one sample-project row holding one ('YXFZJ]4U-=ISt8oh…', 68 chars) was made outside REST. Do not wait on it.