Add warning on compact (#6052)

This PR introduces the ability for `core` to send `warnings` as it can
send `errors. It also sends a warning on compaction.

<img width="811" height="187" alt="image"
src="https://github.com/user-attachments/assets/0947a42d-b720-420d-b7fd-115f8a65a46a"
/>

codex-rs/exec/src/event_processor_with_human_output.rs

@@ -21,6 +21,7 @@ use codex_core::protocol::StreamErrorEvent;
 use codex_core::protocol::TaskCompleteEvent;
 use codex_core::protocol::TurnAbortReason;
 use codex_core::protocol::TurnDiffEvent;
+use codex_core::protocol::WarningEvent;
 use codex_core::protocol::WebSearchEndEvent;
 use codex_protocol::num_format::format_with_separators;
 use owo_colors::OwoColorize;
@@ -54,6 +55,7 @@ pub(crate) struct EventProcessorWithHumanOutput {
     red: Style,
     green: Style,
     cyan: Style,
+    yellow: Style,
 
     /// Whether to include `AgentReasoning` events in the output.
     show_agent_reasoning: bool,
@@ -81,6 +83,7 @@ impl EventProcessorWithHumanOutput {
                 red: Style::new().red(),
                 green: Style::new().green(),
                 cyan: Style::new().cyan(),
+                yellow: Style::new().yellow(),
                 show_agent_reasoning: !config.hide_agent_reasoning,
                 show_raw_agent_reasoning: config.show_raw_agent_reasoning,
                 last_message_path,
@@ -97,6 +100,7 @@ impl EventProcessorWithHumanOutput {
                 red: Style::new(),
                 green: Style::new(),
                 cyan: Style::new(),
+                yellow: Style::new(),
                 show_agent_reasoning: !config.hide_agent_reasoning,
                 show_raw_agent_reasoning: config.show_raw_agent_reasoning,
                 last_message_path,
@@ -161,6 +165,13 @@ impl EventProcessor for EventProcessorWithHumanOutput {
                 let prefix = "ERROR:".style(self.red);
                 ts_msg!(self, "{prefix} {message}");
             }
+            EventMsg::Warning(WarningEvent { message }) => {
+                ts_msg!(
+                    self,
+                    "{} {message}",
+                    "warning:".style(self.yellow).style(self.bold)
+                );
+            }
             EventMsg::DeprecationNotice(DeprecationNoticeEvent { summary, details }) => {
                 ts_msg!(
                     self,

codex-rs/exec/src/event_processor_with_jsonl_output.rs

@@ -8,6 +8,7 @@ use crate::event_processor::handle_last_message;
 use crate::exec_events::AgentMessageItem;
 use crate::exec_events::CommandExecutionItem;
 use crate::exec_events::CommandExecutionStatus;
+use crate::exec_events::ErrorItem;
 use crate::exec_events::FileChangeItem;
 use crate::exec_events::FileUpdateChange;
 use crate::exec_events::ItemCompletedEvent;
@@ -129,6 +130,15 @@ impl EventProcessorWithJsonOutput {
                 self.last_critical_error = Some(error.clone());
                 vec![ThreadEvent::Error(error)]
             }
+            EventMsg::Warning(ev) => {
+                let item = ThreadItem {
+                    id: self.get_next_item_id(),
+                    details: ThreadItemDetails::Error(ErrorItem {
+                        message: ev.message.clone(),
+                    }),
+                };
+                vec![ThreadEvent::ItemCompleted(ItemCompletedEvent { item })]
+            }
             EventMsg::StreamError(ev) => vec![ThreadEvent::Error(ThreadErrorEvent {
                 message: ev.message.clone(),
             })],