Add MCP tool call spans (#15659)

## Summary
- add an explicit `mcp.tools.call` span around MCP tool execution in
core
- keep MCP span validation local to `mcp_tool_call_tests` instead of
broadening the integration test suite
- inline the turn/session correlation fields directly in the span
initializer

## Included Changes
- `codex-rs/core/src/mcp_tool_call.rs`: wrap the existing MCP tool call
in `mcp.tools.call` and inline `conversation.id`, `session.id`, and
`turn.id` in the span initializer
- `codex-rs/core/src/mcp_tool_call_tests.rs`: assert the MCP span
records the expected correlation and server fields

## Testing
- `cargo test -p codex-core`
- `just fmt`

## Notes
- `cargo test -p codex-core` still hits existing unrelated failures in
guardian-config tests and the sandboxed JS REPL `mktemp` test
- metric work moved to stacked PR #15792
- transport-level RMCP spans and trace propagation remain in stacked PR
#15792
- full workspace `cargo test` was not run

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/core/src/mcp_tool_call.rs

@@ -50,6 +50,10 @@ use serde::Serialize;
 use std::path::Path;
 use std::sync::Arc;
 use toml_edit::value;
+use tracing::Instrument;
+use tracing::Span;
+use tracing::field::Empty;
+use url::Url;
 
 /// Handles the specified tool call dispatches the appropriate
 /// `McpToolCallBegin` and `McpToolCallEnd` events to the `Session`.
@@ -121,6 +125,19 @@ pub(crate) async fn handle_mcp_tool_call(
     }
     let request_meta =
         build_mcp_tool_call_request_meta(turn_context.as_ref(), &server, metadata.as_ref());
+    let connector_id = metadata
+        .as_ref()
+        .and_then(|metadata| metadata.connector_id.clone());
+    let connector_name = metadata
+        .as_ref()
+        .and_then(|metadata| metadata.connector_name.clone());
+    let server_origin = sess
+        .services
+        .mcp_connection_manager
+        .read()
+        .await
+        .server_origin(&server)
+        .map(str::to_string);
 
     let tool_call_begin_event = EventMsg::McpToolCallBegin(McpToolCallBeginEvent {
         call_id: call_id.clone(),
@@ -145,15 +162,29 @@ pub(crate) async fn handle_mcp_tool_call(
                 maybe_mark_thread_memory_mode_polluted(sess.as_ref(), turn_context.as_ref()).await;
 
                 let start = Instant::now();
-                let result = sess
-                    .call_tool(
+                let result = async {
+                    sess.call_tool(
                         &server,
                         &tool_name,
                         arguments_value.clone(),
                         request_meta.clone(),
                     )
                     .await
-                    .map_err(|e| format!("tool call error: {e:?}"));
+                    .map_err(|e| format!("tool call error: {e:?}"))
+                }
+                .instrument(mcp_tool_call_span(
+                    sess.as_ref(),
+                    turn_context.as_ref(),
+                    McpToolCallSpanFields {
+                        server_name: &server,
+                        tool_name: &tool_name,
+                        call_id: &call_id,
+                        server_origin: server_origin.as_deref(),
+                        connector_id: connector_id.as_deref(),
+                        connector_name: connector_name.as_deref(),
+                    },
+                ))
+                .await;
                 let result = sanitize_mcp_tool_result_for_model(
                     turn_context
                         .model_info
@@ -161,8 +192,8 @@ pub(crate) async fn handle_mcp_tool_call(
                         .contains(&InputModality::Image),
                     result,
                 );
-                if let Err(e) = &result {
-                    tracing::warn!("MCP tool call error: {e:?}");
+                if let Err(error) = &result {
+                    tracing::warn!("MCP tool call error: {error:?}");
                 }
                 let tool_call_end_event = EventMsg::McpToolCallEnd(McpToolCallEndEvent {
                     call_id: call_id.clone(),
@@ -236,10 +267,24 @@ pub(crate) async fn handle_mcp_tool_call(
 
     let start = Instant::now();
     // Perform the tool call.
-    let result = sess
-        .call_tool(&server, &tool_name, arguments_value.clone(), request_meta)
-        .await
-        .map_err(|e| format!("tool call error: {e:?}"));
+    let result = async {
+        sess.call_tool(&server, &tool_name, arguments_value.clone(), request_meta)
+            .await
+            .map_err(|e| format!("tool call error: {e:?}"))
+    }
+    .instrument(mcp_tool_call_span(
+        sess.as_ref(),
+        turn_context.as_ref(),
+        McpToolCallSpanFields {
+            server_name: &server,
+            tool_name: &tool_name,
+            call_id: &call_id,
+            server_origin: server_origin.as_deref(),
+            connector_id: connector_id.as_deref(),
+            connector_name: connector_name.as_deref(),
+        },
+    ))
+    .await;
     let result = sanitize_mcp_tool_result_for_model(
         turn_context
             .model_info
@@ -247,8 +292,8 @@ pub(crate) async fn handle_mcp_tool_call(
             .contains(&InputModality::Image),
         result,
     );
-    if let Err(e) = &result {
-        tracing::warn!("MCP tool call error: {e:?}");
+    if let Err(error) = &result {
+        tracing::warn!("MCP tool call error: {error:?}");
     }
     let tool_call_end_event = EventMsg::McpToolCallEnd(McpToolCallEndEvent {
         call_id: call_id.clone(),
@@ -273,6 +318,62 @@ pub(crate) async fn handle_mcp_tool_call(
     CallToolResult::from_result(result)
 }
 
+fn mcp_tool_call_span(
+    session: &Session,
+    turn_context: &TurnContext,
+    fields: McpToolCallSpanFields<'_>,
+) -> Span {
+    let transport = match fields.server_origin {
+        Some("stdio") => "stdio",
+        Some(_) => "streamable_http",
+        None => "",
+    };
+    let span = tracing::info_span!(
+        "mcp.tools.call",
+        otel.kind = "client",
+        rpc.system = "jsonrpc",
+        rpc.method = "tools/call",
+        mcp.server.name = fields.server_name,
+        mcp.server.origin = fields.server_origin.unwrap_or(""),
+        mcp.transport = transport,
+        mcp.connector.id = fields.connector_id.unwrap_or(""),
+        mcp.connector.name = fields.connector_name.unwrap_or(""),
+        tool.name = fields.tool_name,
+        tool.call_id = fields.call_id,
+        conversation.id = %session.conversation_id,
+        session.id = %session.conversation_id,
+        turn.id = turn_context.sub_id.as_str(),
+        server.address = Empty,
+        server.port = Empty,
+    );
+    record_server_fields(&span, fields.server_origin);
+    span
+}
+
+struct McpToolCallSpanFields<'a> {
+    server_name: &'a str,
+    tool_name: &'a str,
+    call_id: &'a str,
+    server_origin: Option<&'a str>,
+    connector_id: Option<&'a str>,
+    connector_name: Option<&'a str>,
+}
+
+fn record_server_fields(span: &Span, url: Option<&str>) {
+    let Some(url) = url else {
+        return;
+    };
+    let Ok(parsed) = Url::parse(url) else {
+        return;
+    };
+    if let Some(host) = parsed.host_str() {
+        span.record("server.address", host);
+    }
+    if let Some(port) = parsed.port_or_known_default() {
+        span.record("server.port", port as i64);
+    }
+}
+
 async fn maybe_mark_thread_memory_mode_polluted(sess: &Session, turn_context: &TurnContext) {
     if !turn_context
         .config

codex-rs/core/src/mcp_tool_call_tests.rs

@@ -18,6 +18,10 @@ use serde::Deserialize;
 use std::collections::HashMap;
 use std::sync::Arc;
 use tempfile::tempdir;
+use tracing::Instrument;
+use tracing::Level;
+use tracing_subscriber::fmt::format::FmtSpan;
+use tracing_test::internal::MockWriter;
 
 fn annotations(
     read_only: Option<bool>,
@@ -119,6 +123,57 @@ fn approval_question_text_prepends_safety_reason() {
     );
 }
 
+#[tokio::test]
+async fn mcp_tool_call_span_records_expected_fields() {
+    let buffer: &'static std::sync::Mutex<Vec<u8>> =
+        Box::leak(Box::new(std::sync::Mutex::new(Vec::new())));
+    let subscriber = tracing_subscriber::fmt()
+        .with_level(true)
+        .with_ansi(false)
+        .with_max_level(Level::TRACE)
+        .with_span_events(FmtSpan::FULL)
+        .with_writer(MockWriter::new(buffer))
+        .finish();
+    let _guard = tracing::subscriber::set_default(subscriber);
+
+    let (session, turn_context) = make_session_and_context().await;
+
+    async {}
+        .instrument(mcp_tool_call_span(
+            &session,
+            &turn_context,
+            McpToolCallSpanFields {
+                server_name: "rmcp",
+                tool_name: "echo",
+                call_id: "call-123",
+                server_origin: Some("https://example.com:8443/mcp"),
+                connector_id: Some("calendar"),
+                connector_name: Some("Calendar"),
+            },
+        ))
+        .await;
+
+    let logs = String::from_utf8(buffer.lock().expect("buffer lock").clone()).expect("utf8 logs");
+    assert!(
+        logs.contains("mcp.tools.call{otel.kind=\"client\"")
+            && logs.contains("rpc.system=\"jsonrpc\"")
+            && logs.contains("rpc.method=\"tools/call\"")
+            && logs.contains("mcp.server.name=\"rmcp\"")
+            && logs.contains("mcp.server.origin=\"https://example.com:8443/mcp\"")
+            && logs.contains("mcp.transport=\"streamable_http\"")
+            && logs.contains("mcp.connector.id=\"calendar\"")
+            && logs.contains("mcp.connector.name=\"Calendar\"")
+            && logs.contains("tool.name=\"echo\"")
+            && logs.contains("tool.call_id=\"call-123\"")
+            && logs.contains("server.address=\"example.com\"")
+            && logs.contains("server.port=8443")
+            && logs.contains("conversation.id=")
+            && logs.contains("session.id=")
+            && logs.contains("turn.id="),
+        "missing MCP tool span fields\nlogs:\n{logs}"
+    );
+}
+
 #[tokio::test]
 async fn approval_elicitation_request_uses_message_override_and_preserves_tool_params_keys() {
     let (session, turn_context) = make_session_and_context().await;