Concatenate nested JSON structures using jq

Edit: updated question as example was too simplified to cover specific case:

Suppose I have a json object:

{
  "items": [
    {
      "details": {
        "name": "test",
        "description": "description"
      },
      "properties": [
        {
          "property1": "someValue",
          "property2": "someOtherValue"
        }
      ],
      "additionalProperties": {
        "other": "stuff"
      }
    },
    {
      "details": {
        "name": "test2",
        "description": "description2"
      },
      "properties": [
        {
          "property1": "someValue2",
          "property2": "someOtherValue2"
        }
      ],
      "additionalProperties": {
        "other": "stuff"
      }
    }
  ]
}

I would like to extract the two json objects details and properties and and insert into item, replacing all other properties. In this example there are additionalProperties that should be ignored, but there could be up to n other properties that should also be ignored.

Desired output:

{
  "items": [
    {
      "name": "test",
      "description": "description",
      "properties": [
        {
          "property1": "someValue2",
          "property2": "someOtherValue2"
        }
      ]
    },
    {
      "name": "test2",
      "description": "description2",
      "properties": [
        {
          "property1": "someValue2",
          "property2": "someOtherValue2"
        }
      ]
    }
  ]
}

I have tried a few different ways using map - but I'm not sure if this is the correct approach. I've seen similar solutions involving reduce too, however I am yet to get something that works. Any help would be appreciated!

Update |= each item in the .items array by adding up .details and .properties:

jq '.items[] |= .details + .properties'

{
  "items": [
    {
      "name": "test",
      "description": "description",
      "property1": "someValue",
      "property2": "someOtherValue"
    },
    {
      "name": "test2",
      "description": "description2",
      "property1": "someValue2",
      "property2": "someOtherValue2"
    }
  ]
}

Demo

Edit: With the updated input files, just add {properties} as is (replacing .properties):

jq '.items[] |= .details + {properties}'

{
  "items": [
    {
      "name": "test",
      "description": "description",
      "properties": [
        {
          "property1": "someValue",
          "property2": "someOtherValue"
        }
      ]
    },
    {
      "name": "test2",
      "description": "description2",
      "properties": [
        {
          "property1": "someValue2",
          "property2": "someOtherValue2"
        }
      ]
    }
  ]
}

Demo

With * operator:

jq '.items[] |= (.details * .properties[])' test.json

{
  "items": [
    {
      "name": "test",
      "description": "description",
      "property1": "someValue",
      "property2": "someOtherValue"
    },
    {
      "name": "test2",
      "description": "description2",
      "property1": "someValue2",
      "property2": "someOtherValue2"
    }
  ]
}

I have managed to get the desired output with the following:

jq '.items[] |= .details + {"properties": .properties}'

ideally I don't want to specify the key "properties" but am yet to find another way

There are many possible solutions as evidenced by the existing great answers. One solution takes the constructive, albeit slightly repetetive, approach:

{
    items: .items | map({
        name: .details.name,
        description: .details.description,
        properties
    })
}

Similarly, you can re-construct the items of the array and then update-assign them:

.items[] |= {
    name: .details.name,
    description: .details.description,
    properties
}