chore: persist turn_id in rollout session and make turn_id uuid based (#11246)

Problem:
1. turn id is constructed in-memory;
2. on resuming threads, turn_id might not be unique;
3. client cannot no the boundary of a turn from rollout files easily.

This PR does three things:
1. persist `task_started` and `task_complete` events;
1. persist `turn_id` in rollout turn events;
5. generate turn_id as unique uuids instead of incrementing it in
memory.

This helps us resolve the issue of clients wanting to have unique turn
ids for resuming a thread, and knowing the boundry of each turn in
rollout files.

example debug logs
```
2026-02-11T00:32:10.746876Z DEBUG codex_app_server_protocol::protocol::thread_history: built turn from rollout items turn_index=8 turn=Turn { id: "019c4a07-d809-74c3-bc4b-fd9618487b4b", items: [UserMessage { id: "item-24", content: [Text { text: "hi", text_elements: [] }] }, AgentMessage { id: "item-25", text: "Hi. I’m in the workspace with your current changes loaded and ready. Send the next task and I’ll execute it end-to-end." }], status: Completed, error: None }
2026-02-11T00:32:10.746888Z DEBUG codex_app_server_protocol::protocol::thread_history: built turn from rollout items turn_index=9 turn=Turn { id: "019c4a18-1004-76c0-a0fb-a77610f6a9b8", items: [UserMessage { id: "item-26", content: [Text { text: "hello", text_elements: [] }] }, AgentMessage { id: "item-27", text: "Hello. Ready for the next change in `codex-rs`; I can continue from the current in-progress diff or start a new task." }], status: Completed, error: None }
2026-02-11T00:32:10.746899Z DEBUG codex_app_server_protocol::protocol::thread_history: built turn from rollout items turn_index=10 turn=Turn { id: "019c4a19-41f0-7db0-ad78-74f1503baeb8", items: [UserMessage { id: "item-28", content: [Text { text: "hello", text_elements: [] }] }, AgentMessage { id: "item-29", text: "Hello. Send the specific change you want in `codex-rs`, and I’ll implement it and run the required checks." }], status: Completed, error: None }
```

backward compatibility:
if you try to resume an old session without task_started and
task_complete event populated, the following happens:
- If you resume and do nothing: those reconstructed historical IDs can
differ next time you resume.
- If you resume and send a new turn: the new turn gets a fresh UUID from
live submission flow and is persisted, so that new turn’s ID is stable
on later resumes.
I think this behavior is fine, because we only care about deterministic
turn id once a turn is triggered.

codex-rs/protocol/src/protocol.rs

@@ -1152,11 +1152,13 @@ pub struct ContextCompactedEvent;
 
 #[derive(Debug, Clone, Deserialize, Serialize, JsonSchema, TS)]
 pub struct TurnCompleteEvent {
+    pub turn_id: String,
     pub last_agent_message: Option<String>,
 }
 
 #[derive(Debug, Clone, Deserialize, Serialize, JsonSchema, TS)]
 pub struct TurnStartedEvent {
+    pub turn_id: String,
     // TODO(aibrahim): make this not optional
     pub model_context_window: Option<i64>,
     #[serde(default)]
@@ -1740,6 +1742,8 @@ impl From<CompactedItem> for ResponseItem {
 
 #[derive(Serialize, Deserialize, Clone, Debug, JsonSchema, TS)]
 pub struct TurnContextItem {
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub turn_id: Option<String>,
     pub cwd: PathBuf,
     pub approval_policy: AskForApproval,
     pub sandbox_policy: SandboxPolicy,
@@ -2402,6 +2406,7 @@ pub struct Chunk {
 
 #[derive(Debug, Clone, Deserialize, Serialize, JsonSchema, TS)]
 pub struct TurnAbortedEvent {
+    pub turn_id: Option<String>,
     pub reason: TurnAbortReason,
 }
 
@@ -2690,6 +2695,24 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn turn_aborted_event_deserializes_without_turn_id() -> Result<()> {
+        let event: EventMsg = serde_json::from_value(json!({
+            "type": "turn_aborted",
+            "reason": "interrupted",
+        }))?;
+
+        match event {
+            EventMsg::TurnAborted(TurnAbortedEvent { turn_id, reason }) => {
+                assert_eq!(turn_id, None);
+                assert_eq!(reason, TurnAbortReason::Interrupted);
+            }
+            _ => panic!("expected turn_aborted event"),
+        }
+
+        Ok(())
+    }
+
     /// Serialize Event to verify that its JSON representation has the expected
     /// amount of nesting.
     #[test]