checkbox: Flow PT field type reference

Data type checkbox, probed on Version.flagged (stock, editable). Version.client_approved, sg_movie_has_slate, sg_frames_have_slate and Project.is_template, is_demo, archived are the same type and behave identically.

Read A plain JSON boolean under attributes: true or false, never null, never a string. The schema exposes no default_value and no valid_values.

Every measured route to a null state:

measured	result
100 newest Versions on the sample project, all four checkboxes	`False` (bool), 100%
20 oldest rows on the site, all four checkboxes	`False` (bool), 100%
`Project` site-wide, 22 projects	`is_template` {False, True}, `is_demo` {False, True}, `archived` {False}
`POST` create with the key omitted from the body	reads back `false`, matches `flagged is False` immediately
`_summarize` grouping on `flagged`	`[('[ ]', 100)]`, a ticked row `[X]`; two groups, no third
`is true` + `is false` over the 100-row baseline	0 + 100 = 100 = baseline, nothing left over

The 201 response from a create omits the field entirely; read the row back.

Write true, false, "true" and "false" only. Same on POST (create) and PUT (update).

sent	result
`true`	200, reads back `True`
`"true"`	200, reads back `True`
`false`	200, reads back `False`
`"false"`	200, reads back `False`
`null`	400 `API update() Version.flagged expected [String, FalseClass, TrueClass] data type(s) but got NilClass: nil`
`1`	400 `... but got Integer: 1`
`0`	400 `... but got Integer: 0`
`"1"`	400 `Invalid data for 'checkbox' data type. Value: 1`
`"0"`, `"yes"`, `""`, `"checked"`	400 `Invalid data for 'checkbox' data type. Value: <as sent>`
`null` on `POST` create	400 `API create() ... got NilClass: nil`

Clear

sent	result
`false`	200, value becomes `False`
`null`	400, value stays `True`
`""`	400, value stays `True`

false is the only off state. A client that models unset as None and PUTs it gets a 400, and a partial update built by dropping null-valued keys skips the field instead of clearing it.

Filter The relation list, from the API's own rejection of a bogus operator:

["flagged", "definitely_not_an_operator", null] -> 400
 title:  "API read() Version.flagged's 'checkbox' data type doesn't support
          'definitely_not_an_operator' 'relation'"
 source: {"Version.flagged": " data type doesn't support 'definitely_not_an_operator' 'relation'.
          Value: {"path" => "flagged", "relation" => "definitely_not_an_operator", "values" => [nil]}
          Valid relations: ["is", "is_not"]"}

operator	value	matches
`is`	`true`	ticked rows; `"true"` returns the same ids
`is`	`false`	unticked rows; `"false"` returns the same ids
`is_not`	`true`	unticked rows
`is_not`	`false`	ticked rows

Counts on a 100-Version baseline where every row is false, and on three sandbox rows with one ticked. The sandbox column compares the ids returned, not the counts: equal counts would not prove equal rows.

filter	baseline	sandbox, 3 rows
`is true`	0	1, the ticked id
`is false`	100	2, the two untouched ids
`is "true"`	0	1, the same id as `is true`
`is "false"`	100	2, the same ids as `is false`
`is_not true`	100	2, the same ids as `is false`
`is_not false`	0	1, the same id as `is true`

rejected filter	result
`is 1`	400 `API read() Version.flagged expected [String, FalseClass, TrueClass] ... got Integer: 1`
`is "1"`	400 `Invalid data for 'checkbox' data type. Value: 1`
`is null`	400 `API read() Version.flagged expected [String, FalseClass, TrueClass] data type(s) but got NilClass: nil`
`is_not null`	400 same body from `_search`; `_summarize` gives `API summarize() ...` (probe 020)
`in [true, false]`	400 `Valid relations: ["is", "is_not"]`

Ask for unticked rows as ["flagged", "is", false], not is_not true, though both returned the same ids here; is_not None cannot be asked at all.

Traps

Fill rate is meaningless on this type. Every checkbox on every row is non-null, so a fill-rate scan reports 100% for all four Version checkboxes while every row holds the same value (probe 007). Drop data_type == "checkbox" from fill ranking before scoring; no threshold separates an informative checkbox from a dead one.
The is_not None fill-rate filter that works on every other type 400s here, in both _search and _summarize (probe 020). Special-case the type; do not catch the 400 and score 0.
_summarize returns the UI glyph, not the value, so the empty-group trick that yields an empty count on a list field ([('<value>', 99), ('', 1)]) never sees '' here and reports the field fully populated.
A checkbox can be refused on both paths. Note.client_note is editable: false and answers 400 API create() Client Notes can not be created through the API to a create sending true and 400 API update() Note.client_note is editable on create only. to every update, false included, so there is no value a caller can put in it (probe 069).
Strings coerce on read and write ("true" -> True), so a checkbox set from a CSV or a form post works until someone sends "1". That 400s with a different error shape (Invalid data for 'checkbox' data type, under source) than a bare 1 (expected [String, FalseClass, TrueClass] ... got Integer). Match on the status, not the title.