[codex-analytics] feature plumbing and emittance (#16640)

---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/openai/codex/pull/16640).
* #16870
* #16706
* #16641
* __->__ #16640

codex-rs/core/src/state/session.rs

@@ -33,6 +33,7 @@ pub(crate) struct SessionState {
     pub(crate) active_connector_selection: HashSet<String>,
     pub(crate) pending_session_start_source: Option<codex_hooks::SessionStartSource>,
     granted_permissions: Option<PermissionProfile>,
+    next_turn_is_first: bool,
 }
 
 impl SessionState {
@@ -51,6 +52,7 @@ impl SessionState {
             active_connector_selection: HashSet::new(),
             pending_session_start_source: None,
             granted_permissions: None,
+            next_turn_is_first: true,
         }
     }
 
@@ -73,6 +75,16 @@ impl SessionState {
         self.previous_turn_settings = previous_turn_settings;
     }
 
+    pub(crate) fn set_next_turn_is_first(&mut self, value: bool) {
+        self.next_turn_is_first = value;
+    }
+
+    pub(crate) fn take_next_turn_is_first(&mut self) -> bool {
+        let is_first_turn = self.next_turn_is_first;
+        self.next_turn_is_first = false;
+        is_first_turn
+    }
+
     pub(crate) fn clone_history(&self) -> ContextManager {
         self.history.clone()
     }