feat: add compaction event (#7289)

codex-rs/protocol/src/protocol.rs

@@ -455,6 +455,9 @@ pub enum EventMsg {
     /// indicates the task continued but the user should still be notified.
     Warning(WarningEvent),
 
+    /// Conversation history was compacted (either automatically or manually).
+    ContextCompacted(ContextCompactedEvent),
+
     /// Agent has started a task
     TaskStarted(TaskStartedEvent),
 
@@ -739,6 +742,9 @@ pub struct WarningEvent {
     pub message: String,
 }
 
+#[derive(Debug, Clone, Deserialize, Serialize, JsonSchema, TS)]
+pub struct ContextCompactedEvent;
+
 #[derive(Debug, Clone, Deserialize, Serialize, JsonSchema, TS)]
 pub struct TaskCompleteEvent {
     pub last_agent_message: Option<String>,