fix: skip example checks in instance data

[FanouZeng-TT]

Description

check_examples walked every object and array value below a schema node. default, const, examples, and enum hold JSON instance data, so a business object such as { "type": "string", "examples": [123] } inside one of those keywords was reinterpreted as a schema and reported as E008.

Fix: skip those four instance-data keyword values during example traversal while preserving validation at real schema locations. The regression test covers all four keywords, and the existing invalid-example test continues to protect real examples arrays.

Category (Required)

• Core Protocol: Changes to core protocol specifications. (Requires Technical Council approval)
• Governance/Contributing: Changes to governance or contributing processes. (Requires Governance Council approval)
• Capability: New or updated capabilities. (Requires Maintainer approval)
• Documentation: Documentation-only changes. (Requires Maintainer approval)
• Infrastructure: Build, CI, or deployment changes. (Requires DevOps Maintainer approval)
• Maintenance: Dependencies and repository maintenance. (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. (Requires Maintainer approval)
• Community Health (.github): Organization-wide community files. (Requires DevOps Maintainer approval)

Related Issues

N/A

Checklist

• I have followed the Contributing Guide and Code of Conduct.
• I have updated the documentation (if applicable).
• 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 (not applicable).

Screenshots / Logs (if applicable)

N/A — verified with cargo test --all-targets, cargo clippy --all-targets -- -D warnings, cargo fmt --check, all pre-commit hooks, and git diff --check.

[damaz91]

Thanks for submitting this fix @FanouZeng-TT!

A couple of quick observations and suggestions:

1. Property Name Collisions (under properties / $defs):
   Because check_examples does a generic JSON tree traversal, checking key.as_str() directly inside for (key, child) in map will also cause subschemas of properties named "default", "const", "examples", or "enum" to be skipped (e.g., properties: { "default": { "type": "string", "examples": [123] } }).

   To avoid missing example checks on properties with these names, we could check if we are inside a properties / $defs container (or ensure children of properties are always treated as subschemas).

2. Singular "example" keyword (OpenAPI):
   OpenAPI 3.0 / JSON Schema Draft-04 schemas often use the singular "example" keyword for instance data. It might be worth adding "example" to the list as well:

   if matches!(key.as_str(), "default" | "const" | "examples" | "example" | "enum") {
       continue;
   }

[FanouZeng-TT]

Addressed both points in f3f631c: schema maps (properties, patternProperties, $defs, and definitions) now recurse directly into their values, so property names that collide with instance-data keywords still receive E008 validation. Singular OpenAPI example values are now skipped as instance data as well. Added regression coverage for both cases; all 317 tests, clippy, fmt, pre-commit, and diff check pass.

[FanouZeng-TT]

Small follow-up in aab664d: included dependentSchemas, the other object-valued schema map in Draft 2020-12, and extended the collision regression to cover it. Targeted linter tests, clippy, fmt, pre-commit, and diff check pass.