docs: ISS-179977, Add documentation for mapping custom objects and custom links

fern/docs/pages/airdrop/initial-domain-mapping.mdx

@@ -115,6 +115,12 @@ Use the Chef UI to map record types and fields.
 The UI displays the external record types you defined in external domain metadata and allows you to map them to DevRev objects.
 Map one record type at a time, ensuring you map all required fields and as many optional fields as possible.
 
+#### Mapping as custom object
+The system allows importing record types and categories as custom objects. To achieve this you have to select `new_custom_object` when mapping the record type. For each external record type mapped as a custom object, a new custom **Leaf type** will be defined in DevRev and a **Subtype** will automatically be created. For more details on customization concepts, please refer to the
+[Customization](../customization.mdx) and [Custom Objects](../custom-objects.mdx)  documentation.
+
+The field mapping works the same as for the stock DevRev types, with the difference being that there are significantly fewer fields to map. All the unmapped fields of the external record type will be created as custom fields.
+
 ### Specify fallback mappings
 
 For some required DevRev fields a fallback is required.
@@ -151,6 +157,13 @@ This enables:
 - Raw jq transformations using external fields as input (experimental)
 - Example input data for testing transformations
 
+<Warning>
+The local metadata file is not validated against the snap-in submission.
+</Warning>
+This enables:
+- Raw jq transformations using external fields as input (experimental)
+- Example input data for testing transformations
+
 <Warning>
 The local metadata file is not validated against the snap-in submission.
 </Warning>

fern/docs/pages/airdrop/metadata-extraction.mdx

@@ -504,6 +504,63 @@ be changed by the end user at any time, such as mandatory fields or custom field
   - If a status field has no explicit transitions but you still want a stage diagram, set `all_transitions_allowed` to `true`, which creates a diagram where all the defined stages can transition to each other.
   - External systems may categorize statuses (like Jira's status categories), which can be included in the diagram metadata (`states` in the example).
   - The `starting_stage` defines the initial stage for new object instances. This data should always be provided if available, otherwise the starting stage is selected alphabetically.
-  - In current metadata format (v0.2.0), the order and human-readable name are taken from the enum values defined on the controlling field.
+  - The order and human-readable name are taken from the enum values defined on the controlling field.
   - If the `states` field is not provided, default DevRev states are used: `open`, `in_progress`, and `closed`.
+
+  ### Declare custom link types
+
+  External record types that represent links between other record types can be imported as ***custom links***, which means that each declared link type will be recreated in DevRev with the same names. This allows closer preservation of the original data without the need to map the links to DevRev's predefined link types.
+
+  To achieve this, the external record type needs to have an enum field defined that represents the link types and you need to declare a special field called `link_naming_data` in the record type. 
+
+  ```json
+  {
+    "fields": {
+        "type": {
+            "name": "Link Type",
+            "is_required": true,
+            "type": "enum",
+            "enum": {
+                "values": [
+                    {
+                        "key": "1",
+                        "name": "Parent Of"
+                    },
+                    {
+                        "key": "2",
+                        "name": "Related"
+                    },
+                    {
+                        "key": "3",
+                        "name": "Blocks"
+                    }
+                ]
+            }
+        }
+    },
+    "link_naming_data": {
+        "link_type_field": "type",
+        "link_direction_names": {
+            "1": {
+                "forward_name": "Parent of",
+                "backward_name": "Child of"
+            },
+            "2": {
+                "forward_name": "Relates To",
+                "backward_name": "Relates To"
+            },
+            "3": {
+                "forward_name": "Blocks",
+                "backward_name": "Is Blocked By"
+            }
+        }
+    }
+  }
+  ```
+
+  In the above example:
+  - The external *type* field is declared as the `link_type_field`.
+  - The `link_direction_names` provide a mapping of each value in the `link_type_field` to their directional names. `forward_name` and `backward_name` can be the same, but both are required.
+  - The human-readable name of the link type is taken from the enum values defined on the `link_type_field`. The linkable object types in DevRev are defined based on the mappings of the *source_id* and *target_id* [fields](./supported-object-types.mdx#custom_link#).
+
 </Steps>

fern/docs/pages/airdrop/supported-object-types.mdx

@@ -1,14 +1,14 @@
 # Supported DevRev object types for Airdrop
 
-Last updated: _June 5, 2025_
+Last updated: _June 11, 2025_
 
 This document contains the list of all DevRev object types that are supported for Airdrop.
 
 ## Summary
 
 | Object Type | Object Hierarchy | Loading | Extraction | Subtype | AppFragment | Comment |
 |-------|-------------|:-------:|:----------:|:-------:|:----------:|-------------|
-| [A new custom object type](#a-new-custom-object-type) | custom_object | ✔︎ | ✔︎ | ✔︎ |  |  |
+| [new_custom_object](#new_custom_object) | custom_object | ✔︎ | ✔︎ | ✔︎ |  | _New custom object is an example of how custom objects look in the context of Airdrop mapping._ |
 | [account](#account) | account | ✔︎ |  |  |  |  |
 | [airdrop_authorization_policy](#airdrop_authorization_policy) | airdrop_authorization_policy | ✔︎ |  |  |  | _Airdrop authorization policy object type is the intermediate object type for creating MFZ object types: role, role_set, object_member, and access_control_entry._ |
 | [airdrop_platform_group](#airdrop_platform_group) | airdrop_platform_group | ✔︎ |  |  |  | _Airdrop platform group object type is the representation of the default DevRev groups._ |
@@ -51,7 +51,7 @@ This document contains the list of all DevRev object types that are supported fo
 | Can Subtype | Indicates that the object type supports [subtype](https://developer.devrev.ai/beta/guides/object-customization#subtype) creation. |
 | Can App Fragment | Indicates that the object type supports application fragments. |
 
-## A new custom object type
+## new_custom_object
 
 **Resource Type:** `custom_object`
 
@@ -1650,3 +1650,4 @@ This document contains the list of all DevRev object types that are supported fo
 
 [ ▲ top](#summary)
 
+---