feat: Set chat name (#4974)

Set chat name with `/name` so they appear in the codex resume page:


https://github.com/user-attachments/assets/c0252bba-3a53-44c7-a740-f4690a3ad405

codex-rs/protocol/src/protocol.rs

@@ -171,6 +171,11 @@ pub enum Op {
     /// to generate a summary which will be returned as an AgentMessage event.
     Compact,
 
+    /// Set a human-friendly name for the current session.
+    /// The agent will persist this to the rollout as an event so that UIs can
+    /// surface it when listing sessions.
+    SetSessionName { name: String },
+
     /// Request a code review from the agent.
     Review { review_request: ReviewRequest },
 
@@ -458,6 +463,9 @@ pub enum EventMsg {
     /// Signaled when the model begins a new reasoning summary section (e.g., a new titled block).
     AgentReasoningSectionBreak(AgentReasoningSectionBreakEvent),
 
+    /// Session was given a human-friendly name by the user.
+    SessionRenamed(SessionRenamedEvent),
+
     /// Ack the client's configure message.
     SessionConfigured(SessionConfiguredEvent),
 
@@ -895,6 +903,11 @@ pub struct WebSearchEndEvent {
     pub query: String,
 }
 
+#[derive(Debug, Clone, Deserialize, Serialize, TS)]
+pub struct SessionRenamedEvent {
+    pub name: String,
+}
+
 /// Response payload for `Op::GetHistory` containing the current session's
 /// in-memory transcript.
 #[derive(Debug, Clone, Deserialize, Serialize, TS)]