fix(ucp): constrain resource responses to success status

[pranshu-10]

Description

• Normal Checkout, Cart, Order, and Catalog response schemas inherit the base ucp.status definition, which permits both success and error.

• As a result, a resource-shaped response can incorrectly validate with ucp.status: "error", even though the specification defines:

  • success as carrying the expected resource payload.
  • error as carrying error information instead of a resource.

• This change constrains status to success in the four normal resource
  response schemas:

  • response_checkout_schema
  • response_order_schema
  • response_cart_schema
  • response_catalog_schema

• The field remains optional, so responses that omit status continue to validate. The existing default: "success" documents the default semantics but does not insert the field during JSON Schema validation.

• The separate error-response schema continues to require ucp.status: "error".

• This is a breaking schema tightening because resource-shaped responses that explicitly use ucp.status: "error" were previously accepted and will now be rejected.

  Category (Required)

  • 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

  No related issue.

  Checklist

  • I have followed the Contributing Guide (including Conventional Commits title requirements and
    ! for breaking changes).
  • I have updated the documentation (not applicable; this change enforces the existing documented response semantics).
  • My changes pass all local linting and formatting checks.
  • I have added tests that prove my fix is effective or that my feature works.
  • New and existing unit tests pass locally with my changes.
  • (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)

The following validations were run locally on this branch:

1. Schema lint
   ucp-schema lint source/

2. Example validation
   uv run --frozen python scripts/validate_examples.py --schema-base source/schemas/

3. Validator unit tests
   uv run --frozen python scripts/test_validate_examples.py

4. Targeted schema behavior
   A temporary local validation script checked all four affected response schemas:

             Test case                       Before      After

          Resource with status: "success"     Valid      Valid
 
          Resource with omitted status        Valid      Valid

          Resource with status: "error"       Valid    Invalid

          Proper error response               Valid      Valid