Add MCP tool wall time to model output (#17406)

Include MCP wall time in the output so the model is aware of how long
it's calls are taking.

codex-rs/core/src/tools/context.rs

@@ -118,6 +118,63 @@ impl ToolOutput for CallToolResult {
     }
 }
 
+#[derive(Clone, Debug)]
+pub struct McpToolOutput {
+    pub result: CallToolResult,
+    pub wall_time: Duration,
+}
+
+impl ToolOutput for McpToolOutput {
+    fn log_preview(&self) -> String {
+        let payload = self.response_payload();
+        let preview = payload.body.to_text().unwrap_or_else(|| {
+            serde_json::to_string(&self.result.content)
+                .unwrap_or_else(|err| format!("failed to serialize mcp result: {err}"))
+        });
+        telemetry_preview(&preview)
+    }
+
+    fn success_for_logging(&self) -> bool {
+        self.result.success()
+    }
+
+    fn to_response_item(&self, call_id: &str, _payload: &ToolPayload) -> ResponseInputItem {
+        ResponseInputItem::FunctionCallOutput {
+            call_id: call_id.to_string(),
+            output: self.response_payload(),
+        }
+    }
+
+    fn code_mode_result(&self, _payload: &ToolPayload) -> JsonValue {
+        serde_json::to_value(&self.result).unwrap_or_else(|err| {
+            JsonValue::String(format!("failed to serialize mcp result: {err}"))
+        })
+    }
+}
+
+impl McpToolOutput {
+    fn response_payload(&self) -> FunctionCallOutputPayload {
+        let mut payload = self.result.as_function_call_output_payload();
+        let wall_time_seconds = self.wall_time.as_secs_f64();
+        let header = format!("Wall time: {wall_time_seconds:.4} seconds\nOutput:");
+
+        match &mut payload.body {
+            FunctionCallOutputBody::Text(text) => {
+                if text.is_empty() {
+                    *text = header;
+                } else {
+                    *text = format!("{header}\n{text}");
+                }
+            }
+            FunctionCallOutputBody::ContentItems(items) => {
+                items.insert(0, FunctionCallOutputContentItem::InputText { text: header });
+            }
+        }
+
+        payload
+    }
+}
+
 #[derive(Clone)]
 pub struct ToolSearchOutput {
     pub tools: Vec<ToolSearchOutputTool>,

codex-rs/core/src/tools/context_tests.rs

@@ -85,6 +85,145 @@ fn mcp_code_mode_result_serializes_full_call_tool_result() {
     );
 }
 
+#[test]
+fn mcp_tool_output_response_item_includes_wall_time() {
+    let output = McpToolOutput {
+        result: CallToolResult {
+            content: vec![serde_json::json!({
+                "type": "text",
+                "text": "done",
+            })],
+            structured_content: None,
+            is_error: Some(false),
+            meta: None,
+        },
+        wall_time: std::time::Duration::from_millis(1250),
+    };
+
+    let response = output.to_response_item(
+        "mcp-call-1",
+        &ToolPayload::Mcp {
+            server: "server".to_string(),
+            tool: "tool".to_string(),
+            raw_arguments: "{}".to_string(),
+        },
+    );
+
+    match response {
+        ResponseInputItem::FunctionCallOutput { call_id, output } => {
+            assert_eq!(call_id, "mcp-call-1");
+            assert_eq!(output.success, Some(true));
+            let Some(text) = output.body.to_text() else {
+                panic!("MCP output should serialize as text");
+            };
+            let Some(payload) = text.strip_prefix("Wall time: 1.2500 seconds\nOutput:\n") else {
+                panic!("MCP output should include wall-time header: {text}");
+            };
+            let parsed: serde_json::Value = serde_json::from_str(payload).unwrap_or_else(|err| {
+                panic!("MCP output should serialize JSON content: {err}");
+            });
+            assert_eq!(
+                parsed,
+                json!([{
+                    "type": "text",
+                    "text": "done",
+                }])
+            );
+        }
+        other => panic!("expected FunctionCallOutput, got {other:?}"),
+    }
+}
+
+#[test]
+fn mcp_tool_output_response_item_preserves_content_items() {
+    let image_url = "data:image/png;base64,AAA";
+    let output = McpToolOutput {
+        result: CallToolResult {
+            content: vec![serde_json::json!({
+                "type": "image",
+                "mimeType": "image/png",
+                "data": "AAA",
+            })],
+            structured_content: None,
+            is_error: Some(false),
+            meta: None,
+        },
+        wall_time: std::time::Duration::from_millis(500),
+    };
+
+    let response = output.to_response_item(
+        "mcp-call-2",
+        &ToolPayload::Mcp {
+            server: "server".to_string(),
+            tool: "tool".to_string(),
+            raw_arguments: "{}".to_string(),
+        },
+    );
+
+    match response {
+        ResponseInputItem::FunctionCallOutput { output, .. } => {
+            assert_eq!(
+                output.content_items(),
+                Some(
+                    vec![
+                        FunctionCallOutputContentItem::InputText {
+                            text: "Wall time: 0.5000 seconds\nOutput:".to_string(),
+                        },
+                        FunctionCallOutputContentItem::InputImage {
+                            image_url: image_url.to_string(),
+                            detail: None,
+                        },
+                    ]
+                    .as_slice()
+                )
+            );
+            assert_eq!(
+                output.body.to_text().as_deref(),
+                Some("Wall time: 0.5000 seconds\nOutput:")
+            );
+        }
+        other => panic!("expected FunctionCallOutput, got {other:?}"),
+    }
+}
+
+#[test]
+fn mcp_tool_output_code_mode_result_stays_raw_call_tool_result() {
+    let output = McpToolOutput {
+        result: CallToolResult {
+            content: vec![serde_json::json!({
+                "type": "text",
+                "text": "ignored",
+            })],
+            structured_content: Some(serde_json::json!({
+                "content": "done",
+            })),
+            is_error: Some(false),
+            meta: None,
+        },
+        wall_time: std::time::Duration::from_millis(1250),
+    };
+
+    let result = output.code_mode_result(&ToolPayload::Mcp {
+        server: "server".to_string(),
+        tool: "tool".to_string(),
+        raw_arguments: "{}".to_string(),
+    });
+
+    assert_eq!(
+        result,
+        serde_json::json!({
+            "content": [{
+                "type": "text",
+                "text": "ignored",
+            }],
+            "structuredContent": {
+                "content": "done",
+            },
+            "isError": false,
+        })
+    );
+}
+
 #[test]
 fn custom_tool_calls_can_derive_text_from_content_items() {
     let payload = ToolPayload::Custom {

codex-rs/core/src/tools/handlers/mcp.rs

@@ -1,16 +1,17 @@
 use std::sync::Arc;
+use std::time::Instant;
 
 use crate::function_tool::FunctionCallError;
 use crate::mcp_tool_call::handle_mcp_tool_call;
+use crate::tools::context::McpToolOutput;
 use crate::tools::context::ToolInvocation;
 use crate::tools::context::ToolPayload;
 use crate::tools::registry::ToolHandler;
 use crate::tools::registry::ToolKind;
-use codex_protocol::mcp::CallToolResult;
 
 pub struct McpHandler;
 impl ToolHandler for McpHandler {
-    type Output = CallToolResult;
+    type Output = McpToolOutput;
 
     fn kind(&self) -> ToolKind {
         ToolKind::Mcp
@@ -41,7 +42,8 @@ impl ToolHandler for McpHandler {
         let (server, tool, raw_arguments) = payload;
         let arguments_str = raw_arguments;
 
-        let output = handle_mcp_tool_call(
+        let started = Instant::now();
+        let result = handle_mcp_tool_call(
             Arc::clone(&session),
             &turn,
             call_id.clone(),
@@ -51,6 +53,9 @@ impl ToolHandler for McpHandler {
         )
         .await;
 
-        Ok(output)
+        Ok(McpToolOutput {
+            result,
+            wall_time: started.elapsed(),
+        })
     }
 }