Avoid cloning thread history for token usage replay (#34361)

## What changed

- Resolve the turn ID for restored token usage before sending resume and fork responses, avoiding a clone of the full thread history.
- Add `ThreadHistoryBuilder::active_turn_id` so attribution can inspect the active turn without materializing its items.
- Stop history reconstruction at the latest persisted `TokenCount` and verify that a later tail turn does not receive the replayed usage.

GitOrigin-RevId: 69c4a9fe04770d1a938470afc933431e61670094

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

@@ -274,6 +274,14 @@ impl ThreadHistoryBuilder {
             .or_else(|| self.turns.last().cloned())
     }
 
+    /// Returns the id of the active turn without materializing its items.
+    pub fn active_turn_id(&self) -> Option<&str> {
+        self.current_turn
+            .as_ref()
+            .map(|turn| turn.id.as_str())
+            .or_else(|| self.turns.last().map(|turn| turn.id.as_str()))
+    }
+
     pub fn turn_snapshot(&self, turn_id: &str) -> Option<Turn> {
         self.current_turn
             .as_ref()