rewrite $ref in top-level oneOf/anyOf branches during variant generation

[xiaoxuanz-hub]

Description

Fix _create_single_variant in preprocess_schemas.py to rewrite external $ref links in top-level oneOf/anyOf branches when generating request variant schemas.

Previously, rewrite_refs_to_variants was only called on $refs found inside properties. Schemas that define union types via top-level oneOf/anyOf (with no properties), such as fulfillment_destination.json, had their $refs left pointing to the base response schemas instead of the corresponding request variant files. This caused generated wrapper models like FulfillmentDestinationCreateRequest to incorrectly reference ShippingDestination (response, requires id) instead of ShippingDestinationCreateRequest (request, id optional).

The fix adds a post-processing step after property handling to also rewrite $refs in the variant's top-level oneOf/anyOf branches.

Affected generated models:

• FulfillmentDestinationCreateRequest — now wraps ShippingDestinationCreateRequest | RetailLocationCreateRequest
• FulfillmentDestinationUpdateRequest — now wraps ShippingDestinationUpdateRequest | RetailLocationUpdateRequest

Category (Required)

Please select one or more categories that apply to this change.

• Core Protocol: Changes to the base communication layer, global context, or breaking refactors. (Requires Technical Council approval)
• Governance/Contributing: Updates to GOVERNANCE.md, CONTRIBUTING.md, or CODEOWNERS. (Requires Governance Council approval)
• Capability: New schemas (Discovery, Cart, etc.) or extensions. (Requires Maintainer approval)
• Documentation: Updates to README, or documentations regarding schema or capabilities. (Requires Maintainer approval)
• Infrastructure: CI/CD, Linters, or build scripts. (Requires DevOps Maintainer approval)
• Maintenance: Version bumps, lockfile updates, or minor bug fixes. (Requires DevOps Maintainer approval)
• SDK: Language-specific SDK updates and releases. (Requires DevOps Maintainer approval)
• Samples / Conformance: Maintaining samples and the conformance suite. (Requires Maintainer approval)
• UCP Schema: Changes to the ucp-schema tool (resolver, linter, validator). (Requires Maintainer approval)
• Community Health (.github): Updates to templates, workflows, or org-level configs. (Requires DevOps Maintainer approval)

Related Issues

Fixes #34

Checklist

• I have followed the Contributing Guide.
• I have updated the documentation (if applicable).
• My changes pass all local linting and formatting checks.
• (For Core/Capability) I have included/updated the relevant JSON schemas.
• I have regenerated Python Pydantic models by running generate_models.sh under python_sdk.

Screenshots / Logs (if applicable)

[gemini-code-assist]

Code Review

This pull request enhances the schema preprocessing logic to handle top-level oneOf and anyOf branches, ensuring that external references are correctly rewritten to their corresponding request or update variants. This change is reflected in the updated FulfillmentDestination models. Feedback suggests that the current implementation is too narrow and should be expanded to cover the entire variant object, including allOf and items fields, to prevent base models from being incorrectly referenced in generated request variants.

[ShuoRen-TT]

Hi @xiaoxuanz-hub, I opened #52 to address the separate array-root request variant issue tracked in #37.

The two PRs are complementary: #35 fixes request-variant $ref rewriting for top-level composition branches, while #52 preserves array-root schema shapes and applies nested ucp_request filtering under items and allOf.

I intentionally kept #52 scoped and excluded the whole-variant $ref rewrite and fulfillment model changes already covered by #35. Since both PRs touch _create_single_variant, whichever merges second may need a small mechanical rebase, but their functional scopes do not overlap.