[codex-apps] Filter optional file fields by tool schema

[tsarlandie-oai]

Summary

Codex Apps file parameters are exposed to the model as local paths, uploaded at execution time, and rewritten into provided-file payloads before the MCP tool call.

The rewrite currently includes the documented optional fields mime_type and file_name for every file parameter. Apps with strict schemas can reject those fields when they are not declared.

Changes

• Derive the supported optional file fields from each openai/fileParams parameter's raw input schema before replacing it with the model-visible local-path schema.
• Always include download_url and file_id.
• Include mime_type and file_name only when that specific file parameter's schema accepts them, including schemas that allow additional properties.
• Handle scalar and array file parameters, including items-only arrays, composed schemas, and local JSON Schema references.
• Preserve the existing restriction that only the host-owned Codex Apps MCP server can use this upload path.

This supports tools with different file contracts in the same app: one parameter can accept the optional fields while another remains strict.

Validation

• just test -p codex-mcp
• just test -p codex-core mcp_openai_file
• just test -p codex-core codex_apps_file_params_
• just fix -p codex-mcp
• just fix -p codex-core
• just fmt
• git diff --check
• Manually verified in the Codex Electron app that:
  • a strict file schema receives only download_url and file_id
  • a rich file schema also receives mime_type and file_name

Related: #31330

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[chatgpt-codex-connector]

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[tsarlandie-oai]

I have read the CLA Document and I hereby sign the CLA