009 status lists: Flow PT REST finding

Q Are a project's usable statuses visible over REST, and if so where in the field schema are they?

Endpoint GET /schema/<Type>/fields/sg_status_list ± project_id

Docs claim Status lists are project-scoped; REST cannot see or set some of it.

Actual

200 Version sg_status_list [site-wide]
      top-level keys: ['custom_metadata', 'data_type', 'description', 'editable', 'entity_type', 'mandatory', 'name', 'properties', 'ui_value_displayable', 'unique', 'visible']
      property keys:  ['default_value', 'display_values', 'hidden_values', 'summary_default', 'valid_values']
      valid_values:   ['na', 'rev', 'vwd', 'apr', 'custom', 'fin', 'ip', 'clsd', 'cmpt', 'cfrm', 'pndad', 'pndl', 'pndvs', 'part', 'pass', 'pndng']
      display_values: {"apr": "Approved", "cmpt": "Complete", "ip": "In Progress", "na": "N/A", "rev": "Pending Review", "vwd": "Viewed", "cfrm": "Confirmed", "pndng": "Pending", "fin": "Final", "clsd": "Closed", "custom": "CustomIcon", "pass": "pass", "part": "partial", "pndad": "Pending Art Director", "pndl": "Pending Lead", "pndvs": "Pending VFX Supervisor"}
      hidden_values:  []
      default_value:  "rev"
      editable:       true  mandatory: false
200 Version sg_status_list [project A]
      top-level keys / property keys / valid_values / display_values / default_value: byte-identical to site-wide
      hidden_values:  ["part", "pass", "pndad", "pndl", "pndng", "pndvs"]    -> 10 usable
200 [project B] hidden_values: ["pndl", "pndvs"]              -> 14 usable
200 [project C] hidden_values: ["pass"]                                    -> 15 usable
   ... 17 further projects: 15 hide the same 6, 2 hide ["part", "pass", "pndng"]

distinct valid_values across 21 scopes: 1
200 Task sg_status_list valid_values: ['wtg', 'ip', 'fin', 'apr', 'dis', 'na', 'hld', 'rev', 'omt', 'ready']

Teaches

Usable statuses are valid_values minus hidden_values, read with project_id. REST does not enforce hidden_values on write, so do the subtraction yourself. See field_types/status_list.md.
valid_values is the site's whole vocabulary and is byte-identical at every scope, so reading it alone tells you nothing about a project. On the probed site, 21 scopes returned 1 distinct value.
hidden_values is the only thing project_id changes. Omit project_id and you get the site-wide answer, which hides nothing and will offer statuses the project's UI refuses.
Status lists are per entity type. On the probed site, Version and Task overlap only on ip/fin/apr/na/rev, and Task's wtg/hld/omt/ready do not exist on Version. Never reuse one type's codes for another.
On the probed site, Version's 16 valid_values leave 10 usable in one project, 14 in another and 15 in a third, and 15 of the 21 projects hide the same 6 codes. Which codes a project hides is site configuration, not API behaviour: read it per project rather than reusing a list between sites.
Always render display_values: pndvs means "Pending VFX Supervisor" to nobody, and a missing key there is possible, so fall back to the raw code rather than dropping the option.