[codex-apps] Filter optional file fields by tool schema (#31686)

## 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

codex-rs/codex-mcp/src/rmcp_client.rs

@@ -21,6 +21,7 @@ use std::time::Instant;
 use crate::codex_apps::normalize_codex_apps_callable_name;
 use crate::codex_apps::normalize_codex_apps_callable_namespace;
 use crate::codex_apps::normalize_codex_apps_tool_title;
+use crate::codex_apps::prepare_openai_file_params_for_model;
 use crate::codex_apps_cache::CodexAppsToolsCacheContext;
 use crate::codex_apps_cache::CodexAppsToolsFetchSource;
 use crate::codex_apps_cache::load_startup_cached_codex_apps_server_info;
@@ -34,7 +35,6 @@ use crate::server::McpServerLaunch;
 use crate::tools::ToolFilter;
 use crate::tools::ToolInfo;
 use crate::tools::filter_tools;
-use crate::tools::tool_with_model_visible_input_schema;
 use anyhow::Result;
 use anyhow::anyhow;
 use async_channel::Sender;
@@ -620,7 +620,7 @@ fn prepare_codex_apps_tools_for_model(
     tool_plugin_provenance: &ToolPluginProvenance,
 ) -> Vec<ToolInfo> {
     for tool in &mut tools {
-        tool.tool = tool_with_model_visible_input_schema(&tool.tool);
+        prepare_openai_file_params_for_model(tool);
         let plugin_names = match tool.connector_id.as_deref() {
             Some(connector_id) => {
                 tool_plugin_provenance.plugin_display_names_for_connector_id(connector_id)
@@ -733,6 +733,7 @@ fn codex_apps_tool_info_from_listed_tool(
         callable_namespace,
         namespace_description,
         tool: tool_def,
+        openai_file_input_optional_fields: HashMap::new(),
         connector_id,
         connector_name,
         plugin_display_names: Vec::new(),
@@ -756,6 +757,7 @@ fn regular_mcp_tool_info_from_listed_tool(
         callable_namespace: server_name.to_string(),
         namespace_description: server_instructions.map(str::to_string),
         tool: tool_def,
+        openai_file_input_optional_fields: HashMap::new(),
         connector_id: None,
         connector_name: None,
         plugin_display_names: Vec::new(),
@@ -1138,6 +1140,7 @@ mod tests {
             callable_namespace: "codex_apps__gmail".to_string(),
             namespace_description: Some("Mail connector".to_string()),
             tool: expected_tool,
+            openai_file_input_optional_fields: HashMap::new(),
             connector_id: Some("connector_gmail".to_string()),
             connector_name: Some("Gmail".to_string()),
             plugin_display_names: Vec::new(),