[app-server] fix: emit item/fileChange/outputDelta for file change items

Author: owenlin0

codex-rs/app-server-protocol/src/protocol/common.rs

@@ -510,6 +510,7 @@ server_notification_definitions! {
     ItemCompleted => "item/completed" (v2::ItemCompletedNotification),
     AgentMessageDelta => "item/agentMessage/delta" (v2::AgentMessageDeltaNotification),
     CommandExecutionOutputDelta => "item/commandExecution/outputDelta" (v2::CommandExecutionOutputDeltaNotification),
+    FileChangeOutputDelta => "item/fileChange/outputDelta" (v2::FileChangeOutputDeltaNotification),
     McpToolCallProgress => "item/mcpToolCall/progress" (v2::McpToolCallProgressNotification),
     AccountUpdated => "account/updated" (v2::AccountUpdatedNotification),
     AccountRateLimitsUpdated => "account/rateLimits/updated" (v2::AccountRateLimitsUpdatedNotification),

codex-rs/app-server-protocol/src/protocol/v2.rs

@@ -1295,6 +1295,14 @@ pub struct CommandExecutionOutputDeltaNotification {
     pub delta: String,
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct FileChangeOutputDeltaNotification {
+    pub item_id: String,
+    pub delta: String,
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]

codex-rs/app-server/src/bespoke_event_handling.rs

@@ -18,6 +18,7 @@ use codex_app_server_protocol::ContextCompactedNotification;
 use codex_app_server_protocol::ErrorNotification;
 use codex_app_server_protocol::ExecCommandApprovalParams;
 use codex_app_server_protocol::ExecCommandApprovalResponse;
+use codex_app_server_protocol::FileChangeOutputDeltaNotification;
 use codex_app_server_protocol::FileChangeRequestApprovalParams;
 use codex_app_server_protocol::FileChangeRequestApprovalResponse;
 use codex_app_server_protocol::FileUpdateChange;
@@ -490,15 +491,28 @@ pub(crate) async fn apply_bespoke_event_handling(
                 .await;
         }
         EventMsg::ExecCommandOutputDelta(exec_command_output_delta_event) => {
-            let notification = CommandExecutionOutputDeltaNotification {
-                item_id: exec_command_output_delta_event.call_id.clone(),
-                delta: String::from_utf8_lossy(&exec_command_output_delta_event.chunk).to_string(),
+            let item_id = exec_command_output_delta_event.call_id.clone();
+            let delta = String::from_utf8_lossy(&exec_command_output_delta_event.chunk).to_string();
+            let is_file_change = {
+                let map = turn_summary_store.lock().await;
+                map.get(&conversation_id)
+                    .is_some_and(|summary| summary.file_change_started.contains(&item_id))
             };
-            outgoing
-                .send_server_notification(ServerNotification::CommandExecutionOutputDelta(
-                    notification,
-                ))
-                .await;
+            if is_file_change {
+                let notification = FileChangeOutputDeltaNotification { item_id, delta };
+                outgoing
+                    .send_server_notification(ServerNotification::FileChangeOutputDelta(
+                        notification,
+                    ))
+                    .await;
+            } else {
+                let notification = CommandExecutionOutputDeltaNotification { item_id, delta };
+                outgoing
+                    .send_server_notification(ServerNotification::CommandExecutionOutputDelta(
+                        notification,
+                    ))
+                    .await;
+            }
         }
         EventMsg::ExecCommandEnd(exec_command_end_event) => {
             let ExecCommandEndEvent {

codex-rs/app-server/tests/suite/v2/turn_start.rs

@@ -11,6 +11,7 @@ use app_test_support::to_response;
 use codex_app_server_protocol::ApprovalDecision;
 use codex_app_server_protocol::CommandExecutionRequestApprovalResponse;
 use codex_app_server_protocol::CommandExecutionStatus;
+use codex_app_server_protocol::FileChangeOutputDeltaNotification;
 use codex_app_server_protocol::FileChangeRequestApprovalResponse;
 use codex_app_server_protocol::ItemCompletedNotification;
 use codex_app_server_protocol::ItemStartedNotification;
@@ -725,6 +726,24 @@ async fn turn_start_file_change_approval_v2() -> Result<()> {
     )
     .await?;
 
+    let output_delta_notif = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_notification_message("item/fileChange/outputDelta"),
+    )
+    .await??;
+    let output_delta: FileChangeOutputDeltaNotification = serde_json::from_value(
+        output_delta_notif
+            .params
+            .clone()
+            .expect("item/fileChange/outputDelta params"),
+    )?;
+    assert_eq!(output_delta.item_id, "patch-call");
+    assert!(
+        output_delta.delta.contains("README.md"),
+        "expected delta to mention README.md, got: {}",
+        output_delta.delta
+    );
+
     let completed_file_change = timeout(DEFAULT_READ_TIMEOUT, async {
         loop {
             let completed_notif = mcp