Missing customs field in RateRequest serializer breaks international rate quotes

[jacobshilitz]

Problem

The RateRequest serializer is missing the customs field, causing all customs data to be silently dropped when clients send rate requests. This breaks international rate quotes that require customs information (duty, incoterm, HS codes, etc.).

Root cause: The serializer doesn't accept customs, even though:

• The datatype (datatypes.RateRequest) includes it
• The API schema shows it's expected
• ShipmentContent serializer already has it

Impact

• International rate quotes are inaccurate - Missing customs data means carriers can't calculate proper duties/taxes
• Silent data loss - Clients send customs data, but it's dropped by the serializer
• Workarounds are insufficient - Providers can extract commodities from parcels[].items as a fallback, but this misses critical information like who is paying duties (duty.paid_by), incoterms, invoice details, and other customs metadata required for accurate rate quotes

Evidence

Serializer missing customs:
modules/core/karrio/server/core/serializers.py:654

class RateRequest(validators.OptionDefaultSerializer):
    shipper = AddressData(...)
    recipient = AddressData(...)
    parcels = ParcelData(...)
    # ❌ customs field is missing here
    carrier_ids = serializers.StringListField(...)

But datatype has it:
modules/core/karrio/server/core/datatypes.py:195

class RateRequest(BaseRateRequest):
    customs: Customs = jstruct.JStruct[Customs]  # ✅ Present

And ShipmentContent has it:
modules/core/karrio/server/core/serializers.py:1412

class ShipmentContent(serializers.Serializer):
    customs = CustomsData(...)  # ✅ Present

Solution

Add customs field to RateRequest serializer:

modules/core/karrio/server/core/serializers.py:734

class RateRequest(validators.OptionDefaultSerializer):
    # ... existing fields ...
    reference = serializers.CharField(...)
    customs = CustomsData(
        required=False,
        allow_null=True,
        help_text="""The customs details.<br/>
        **Note that this is required for international shipments.**
        """,
    )
    carrier_ids = serializers.StringListField(...)

Why This Matters for Rating

International rate quotes require customs data to calculate:

• Duties and taxes - Need duty payment info and incoterm (DDP/DDU)
• HS codes - Required for customs classification
• Invoice details - Required for commercial shipments
• Content type - Affects processing fees

Without the customs field, all this data is lost, resulting in inaccurate or incomplete rate quotes.

[jacobshilitz]

see #932

[danh91]

Say no more. Thanks much, it was on my urgent backlog ☺️