mcp: keep elicitation requests below app wire types (#29724)

## Why

Core and tools need to request MCP elicitation without constructing
app-server wire payloads. The request should remain a neutral protocol
concept until app-server serializes it for a client.

## What changed

- Switched core and tools to
`codex_protocol::approvals::ElicitationRequest`.
- Derived turn and server context inside core instead of carrying
app-server request types through lower layers.
- Kept the app-server payload unchanged through an explicit boundary
conversion.
- Removed the remaining production app-server-protocol dependency from
tools.

## Stack

This is PR 5 of 6, stacked on [PR
#29723](https://github.com/openai/codex/pull/29723). Review only the
delta from `codex/split-connector-metadata-types`. Next: [PR
#29725](https://github.com/openai/codex/pull/29725).

## Validation

- `codex-core` MCP coverage passed: 87 tests.
- Tools elicitation and app-server round-trip coverage passed.

codex-rs/core/src/session/mcp.rs

@@ -99,8 +99,9 @@ impl Session {
     pub async fn request_mcp_server_elicitation(
         &self,
         turn_context: &TurnContext,
+        server_name: String,
         request_id: RequestId,
-        params: McpServerElicitationRequestParams,
+        request: ElicitationRequest,
     ) -> McpServerElicitationOutcome {
         if self
             .services
@@ -118,53 +119,6 @@ impl Session {
             };
         }
 
-        let server_name = params.server_name.clone();
-        let request = match params.request {
-            McpServerElicitationRequest::Form {
-                meta,
-                message,
-                requested_schema,
-            } => {
-                let requested_schema = match serde_json::to_value(requested_schema) {
-                    Ok(requested_schema) => requested_schema,
-                    Err(err) => {
-                        warn!(
-                            "failed to serialize MCP elicitation schema for server_name: {server_name}, request_id: {request_id}: {err:#}"
-                        );
-                        return McpServerElicitationOutcome {
-                            response: None,
-                            sent: false,
-                        };
-                    }
-                };
-                codex_protocol::approvals::ElicitationRequest::Form {
-                    meta,
-                    message,
-                    requested_schema,
-                }
-            }
-            McpServerElicitationRequest::OpenAiForm {
-                meta,
-                message,
-                requested_schema,
-            } => codex_protocol::approvals::ElicitationRequest::OpenAiForm {
-                meta,
-                message,
-                requested_schema,
-            },
-            McpServerElicitationRequest::Url {
-                meta,
-                message,
-                url,
-                elicitation_id,
-            } => codex_protocol::approvals::ElicitationRequest::Url {
-                meta,
-                message,
-                url,
-                elicitation_id,
-            },
-        };
-
         let (tx_response, rx_response) = oneshot::channel();
         let prev_entry = {
             let mut active = self.active_turn.lock().await;
@@ -194,7 +148,7 @@ impl Session {
             }
         };
         let event = EventMsg::ElicitationRequest(ElicitationRequestEvent {
-            turn_id: params.turn_id,
+            turn_id: Some(turn_context.sub_id.clone()),
             server_name,
             id,
             request,

codex-rs/core/src/session/mod.rs

@@ -54,8 +54,6 @@ use chrono::Utc;
 use codex_analytics::AnalyticsEventsClient;
 use codex_analytics::SubAgentThreadStartedInput;
 use codex_analytics::TurnCodexErrorFact;
-use codex_app_server_protocol::McpServerElicitationRequest;
-use codex_app_server_protocol::McpServerElicitationRequestParams;
 use codex_config::types::AuthKeyringBackendKind;
 use codex_config::types::OAuthCredentialsStoreMode;
 use codex_exec_server::Environment;
@@ -87,6 +85,7 @@ use codex_otel::current_span_w3c_trace_context;
 use codex_otel::set_parent_from_w3c_trace_context;
 use codex_protocol::SessionId;
 use codex_protocol::ThreadId;
+use codex_protocol::approvals::ElicitationRequest;
 use codex_protocol::approvals::ElicitationRequestEvent;
 use codex_protocol::approvals::ExecPolicyAmendment;
 use codex_protocol::approvals::NetworkPolicyAmendment;

codex-rs/core/src/session/tests.rs

@@ -84,7 +84,6 @@ use crate::tools::handlers::ShellCommandHandler;
 use crate::tools::registry::ToolExecutor;
 use crate::tools::router::ToolCallSource;
 use crate::turn_diff_tracker::TurnDiffTracker;
-use codex_app_server_protocol::McpElicitationSchema;
 use codex_config::config_toml::ConfigToml;
 use codex_config::config_toml::ProjectConfig;
 use codex_config::permissions_toml::FilesystemPermissionToml;
@@ -377,24 +376,18 @@ async fn request_mcp_server_elicitation_auto_accepts_when_auto_deny_is_enabled()
         .load_full()
         .set_elicitations_auto_deny(/*auto_deny*/ true);
 
-    let requested_schema: McpElicitationSchema = serde_json::from_value(json!({
-        "type": "object",
-        "properties": {},
-    }))
-    .expect("schema should deserialize");
     let response = session
         .request_mcp_server_elicitation(
             turn_context.as_ref(),
+            "codex_apps".to_string(),
             RequestId::String("request-1".into()),
-            McpServerElicitationRequestParams {
-                thread_id: session.thread_id.to_string(),
-                turn_id: Some(turn_context.sub_id.clone()),
-                server_name: "codex_apps".to_string(),
-                request: McpServerElicitationRequest::Form {
-                    meta: None,
-                    message: "Allow this request?".to_string(),
-                    requested_schema,
-                },
+            ElicitationRequest::Form {
+                meta: None,
+                message: "Allow this request?".to_string(),
+                requested_schema: json!({
+                    "type": "object",
+                    "properties": {},
+                }),
             },
         )
         .await;