Azure DevOps API - how to discover link between field and picklist - rest

Question

I'm trying to replicate an Azure DevOps process from one organization to another via the AZDO REST Api. I'm working on replicating the layout and am stuck because I can't discover the relationship between a custom field and a picklist when querying the source AZDO instance.
In my scenario I have a test work item type which I've called Issue. On the Issue interface I've created a custom field which is a picklist. While I can retrieve a list of lists via the Rest API and examine the field as well, I can't figure out how the two are related.
Here is a partial payload from the field:
{
"count": 39,
"value": [
...
{
"referenceName": "Custom.IssueSource",
"name": "Issue Source",
"type": "string",
"description": "Who is this attributed to",
"required": true,
"url": "https://dev.azure.com/MYORG/_apis/work/processes/f390103e-7097-4f19-b5b5-f9dbcf92bb6f/behaviors",
"customization": "custom"
},
... ]
}
and here is a partial payload from the lists get query which I used trial and error to determine was the picklist I've assigned:
{
"count": 10,
"value": [
...
{
"id": "2998d4e4-2bec-4935-98a1-b67a0b0b6d5d",
"name": "picklist_e854661e-8620-4ad9-be28-b974c5cb3a5d",
"type": "String",
"isSuggested": false,
"url": "https://dev.azure.com/MYORG/_apis/work/processes/lists/2998d4e4-2bec-4935-98a1-b67a0b0b6d5d"
},
...
]
}
Here is a partial layout response for the WIT:
{
"pages": [
{
"id": "d0171d51-ff84-4038-afc1-8800ab613160.System.WorkItemType.Details",
"inherited": true,
"label": "Details",
"pageType": "custom",
"visible": true,
"isContribution": false,
"sections": [
{
"id": "Section1",
"groups": [
...
{
"id": "bf03e049-5062-4d82-b91d-4396541fbed2",
"label": "Custom",
"isContribution": false,
"visible": true,
"controls": [
{
"id": "Custom.IssueSource",
"label": "Issue Source",
"controlType": "FieldControl",
"readOnly": false,
"visible": true,
"isContribution": false
}
]
}
]
},
... ]
}
Using fiddler against the AZDO web interface, the only time I see a reference to the picklist is from another non-AZDO API to https://dev.azure.com/MYORG/_apis/Contribution/dataProviders/query
Is there a way to discover the link via the AZDO Rest API? I saw this question which was similar but was about creating the link

Answer 1

Figured it out. Turns out you need to query from a different scope - work item tracking rather than work item tracking process:
https://dev.azure.com/MYORG/_apis/wit/fields/Custom.IssueSource?api-version=5.0-preview.2
returns
{
"name": "Issue Source",
"referenceName": "Custom.IssueSource",
"description": "Who is this attributed to",
"type": "string",
"usage": "workItem",
"readOnly": false,
"canSortBy": true,
"isQueryable": true,
...
"isIdentity": false,
--> "isPicklist": true,
"isPicklistSuggested": false,
--> "picklistId": "2998d4e4-2bec-4935-98a1-b67a0b0b6d5d",
"url": "https://dev.azure.com/MYORG/_apis/wit/fields/Custom.IssueSource"
}