chore: add JSON schema policy fixture coverage

[celia-oai]

Why

Before changing the Codex Bridge JSON schema policy, add integration coverage around real connector-like MCP tool schemas. The existing unit tests cover individual sanitizer behaviors, but they do not make it easy to see whether full fixture schemas keep model-visible guidance, prune only unreachable definitions, drop unsupported JSON Schema fields, and stay within the Responses API schema budget.

What Changed

• Added tools/tests/json_schema_policy_fixtures.rs, which converts MCP tool fixtures through mcp_tool_to_responses_api_tool and validates the resulting Responses tool parameters.
• Added connector-style fixtures for Slack, Google Calendar, Google Drive, Notion, and Microsoft Outlook Email under tools/tests/fixtures/json_schema_policy/.
• Added fixture assertions for preserved guidance, pruned definitions, expected field drops after JsonSchema conversion, marker count baselines, and dangling local $ref prevention.
• Added a real oversized golden Notion create_page input schema fixture to exercise the compaction path that strips descriptions, drops root $defs, rewrites local refs, and fits the compacted schema under the budget.

[celia-oai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Keep them coming!

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