[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/connection_manager_tests.rs

@@ -1,7 +1,6 @@
 use super::*;
 use crate::codex_apps_cache::CodexAppsToolsCache;
 use crate::codex_apps_cache::CodexAppsToolsCacheContext;
-use crate::declared_openai_file_input_param_names;
 use crate::elicitation::ElicitationLifecycle;
 use crate::elicitation::ElicitationRequestManager;
 use crate::elicitation::ElicitationRequestRouter;
@@ -19,7 +18,6 @@ use crate::tools::ToolFilter;
 use crate::tools::ToolInfo;
 use crate::tools::filter_tools;
 use crate::tools::normalize_tools_for_model_with_prefix;
-use crate::tools::tool_with_model_visible_input_schema;
 use codex_config::AppToolApproval;
 use codex_config::Constrained;
 use codex_config::McpServerConfig;
@@ -40,9 +38,9 @@ use rmcp::model::CreateElicitationRequestParams;
 use rmcp::model::ElicitationAction;
 use rmcp::model::ElicitationCapability;
 use rmcp::model::JsonObject;
-use rmcp::model::Meta;
 use rmcp::model::NumberOrString;
 use rmcp::model::Tool;
+use std::collections::HashMap;
 use std::collections::HashSet;
 use std::io;
 use std::sync::Arc;
@@ -63,6 +61,7 @@ fn create_test_tool(server_name: &str, tool_name: &str) -> ToolInfo {
             format!("Test tool: {tool_name}"),
             Arc::new(JsonObject::default()),
         ),
+        openai_file_input_optional_fields: Default::default(),
         connector_id: None,
         connector_name: None,
         plugin_display_names: Vec::new(),
@@ -205,85 +204,6 @@ fn is_code_mode_compatible_tool_name(name: &ToolName) -> bool {
         .flat_map(str::chars)
         .all(|c| c.is_ascii_alphanumeric() || c == '_')
 }
-#[test]
-fn declared_openai_file_fields_treat_names_literally() {
-    let meta = serde_json::json!({
-        "openai/fileParams": ["file", "input_file", "attachments"]
-    });
-    let meta = meta.as_object().expect("meta object");
-
-    assert_eq!(
-        declared_openai_file_input_param_names(Some(meta)),
-        vec![
-            "file".to_string(),
-            "input_file".to_string(),
-            "attachments".to_string(),
-        ]
-    );
-}
-
-#[test]
-fn tool_with_model_visible_input_schema_masks_file_params() {
-    let mut tool = create_test_tool(CODEX_APPS_MCP_SERVER_NAME, "upload").tool;
-    tool.input_schema = Arc::new(
-        serde_json::json!({
-            "type": "object",
-            "properties": {
-                "file": {
-                    "type": "object",
-                    "description": "Original file payload."
-                },
-                "files": {
-                    "type": "array",
-                    "items": {"type": "object"}
-                }
-            }
-        })
-        .as_object()
-        .expect("object")
-        .clone(),
-    );
-    tool.meta = Some(Meta(
-        serde_json::json!({
-            "openai/fileParams": ["file", "files"]
-        })
-        .as_object()
-        .expect("object")
-        .clone(),
-    ));
-
-    let tool = tool_with_model_visible_input_schema(&tool);
-
-    assert_eq!(
-        *tool.input_schema,
-        serde_json::json!({
-            "type": "object",
-            "properties": {
-                "file": {
-                    "type": "string",
-                    "description": "Original file payload. This parameter expects an absolute local file path. If you want to upload a file, provide the absolute path to that file here."
-                },
-                "files": {
-                    "type": "array",
-                    "items": {"type": "string"},
-                    "description": "This parameter expects an absolute local file path. If you want to upload a file, provide the absolute path to that file here."
-                }
-            }
-        })
-        .as_object()
-        .expect("object")
-        .clone()
-    );
-}
-
-#[test]
-fn tool_with_model_visible_input_schema_leaves_tools_without_file_params_unchanged() {
-    let original_tool = create_test_tool("custom", "upload").tool;
-
-    let tool = tool_with_model_visible_input_schema(&original_tool);
-
-    assert_eq!(tool, original_tool);
-}
 
 #[test]
 fn elicitation_granular_policy_defaults_to_prompting() {