[codex] preserve MCP result meta in McpToolCallItemResult (#22946)

## Summary

https://openai.slack.com/archives/C0ARA9UAQEA/p1778890981647319?thread_ts=1778888537.934319&cid=C0ARA9UAQEA


- Add `_meta` to exec JSONL MCP tool call result events.
- Copy MCP result metadata through the JSONL event conversion.
- Add a focused test that verifies `_meta` is serialized as `_meta` and
not `meta`.


## Verification

https://www.notion.so/openai/Miaolin-0516-_meta-population-debug-3628e50b62b08074b365e0ce1ffb8f74

codex-rs/exec/src/event_processor_with_jsonl_output.rs

@@ -223,6 +223,7 @@ impl EventProcessorWithJsonOutput {
                     arguments,
                     result: result.map(|result| McpToolCallItemResult {
                         content: result.content,
+                        meta: result.meta,
                         structured_content: result.structured_content,
                     }),
                     error: error.map(|error| McpToolCallItemError {

codex-rs/exec/src/event_processor_with_jsonl_output_tests.rs

@@ -1,5 +1,6 @@
 use super::*;
 use pretty_assertions::assert_eq;
+use serde_json::json;
 use tempfile::tempdir;
 
 #[test]
@@ -57,3 +58,53 @@ fn failed_turn_does_not_overwrite_output_last_message_file() {
         "keep existing contents"
     );
 }
+
+#[test]
+fn mcp_tool_call_result_preserves_meta_in_jsonl_event() {
+    let mut processor = EventProcessorWithJsonOutput::new(/*last_message_path*/ None);
+
+    let collected = processor.collect_thread_events(ServerNotification::ItemCompleted(
+        codex_app_server_protocol::ItemCompletedNotification {
+            item: ThreadItem::McpToolCall {
+                id: "mcp-1".to_string(),
+                server: "search service".to_string(),
+                tool: "web_run".to_string(),
+                status: McpToolCallStatus::Completed,
+                arguments: json!({"search_query": [{"q": "OpenAI Codex CLI documentation"}]}),
+                mcp_app_resource_uri: None,
+                result: Some(Box::new(codex_app_server_protocol::McpToolCallResult {
+                    content: vec![json!({"type": "text", "text": "search result"})],
+                    structured_content: None,
+                    meta: Some(json!({"raw_messages": [{"ref_id": "turn0search0"}]})),
+                })),
+                error: None,
+                duration_ms: Some(42),
+            },
+            thread_id: "thread-1".to_string(),
+            turn_id: "turn-1".to_string(),
+            completed_at_ms: 0,
+        },
+    ));
+
+    assert_eq!(collected.status, CodexStatus::Running);
+    assert_eq!(collected.events.len(), 1);
+
+    let ThreadEvent::ItemCompleted(ItemCompletedEvent { item }) = &collected.events[0] else {
+        panic!("expected item.completed event");
+    };
+    let ThreadItemDetails::McpToolCall(item) = &item.details else {
+        panic!("expected MCP tool call item");
+    };
+    let result = item.result.as_ref().expect("expected MCP tool result");
+    assert_eq!(
+        result.meta,
+        Some(json!({"raw_messages": [{"ref_id": "turn0search0"}]}))
+    );
+
+    let serialized = serde_json::to_value(&collected.events[0]).expect("serialize event");
+    assert_eq!(
+        serialized["item"]["result"]["_meta"],
+        json!({"raw_messages": [{"ref_id": "turn0search0"}]})
+    );
+    assert!(serialized["item"]["result"].get("meta").is_none());
+}

codex-rs/exec/src/exec_events.rs

@@ -266,6 +266,9 @@ pub struct McpToolCallItemResult {
     // representations). Using `JsonValue` keeps the payload wire-shaped and
     // easy to export.
     pub content: Vec<JsonValue>,
+    #[serde(rename = "_meta", skip_serializing_if = "Option::is_none")]
+    #[ts(optional)]
+    pub meta: Option<JsonValue>,
     pub structured_content: Option<JsonValue>,
 }
 

codex-rs/exec/tests/event_processor_with_json_output.rs

@@ -540,6 +540,7 @@ fn mcp_tool_call_begin_and_end_emit_item_events() {
                         arguments: json!({ "key": "value" }),
                         result: Some(McpToolCallItemResult {
                             content: Vec::new(),
+                            meta: None,
                             structured_content: None,
                         }),
                         error: None,
@@ -681,6 +682,7 @@ fn mcp_tool_call_defaults_arguments_and_preserves_structured_content() {
                                 "type": "text",
                                 "text": "done",
                             })],
+                            meta: None,
                             structured_content: Some(json!({ "status": "ok" })),
                         }),
                         error: None,

sdk/typescript/src/items.ts

@@ -60,6 +60,7 @@ export type McpToolCallItem = {
   /** Result payload returned by the MCP server for successful calls. */
   result?: {
     content: McpContentBlock[];
+    _meta?: unknown;
     structured_content: unknown;
   };
   /** Error message reported for failed calls. */