feat: split memories part 2 (#19860)

Keep extracting memories out of core and moving the write trigger in the
app-server
This is temporary and it should move at the client level as a follow-up
This makes core fully independant from `codex-memories-write`

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/core/src/codex_thread.rs

@@ -27,7 +27,6 @@ use codex_protocol::protocol::SandboxPolicy;
 use codex_protocol::protocol::SessionSource;
 use codex_protocol::protocol::Submission;
 use codex_protocol::protocol::ThreadMemoryMode;
-use codex_protocol::protocol::TokenUsage;
 use codex_protocol::protocol::TokenUsageInfo;
 use codex_protocol::protocol::W3cTraceContext;
 use codex_protocol::user_input::UserInput;
@@ -86,6 +85,7 @@ pub struct CodexThreadTurnContextOverrides {
 
 pub struct CodexThread {
     pub(crate) codex: Codex,
+    pub(crate) session_source: SessionSource,
     rollout_path: Option<PathBuf>,
     out_of_band_elicitation_count: Mutex<u64>,
     _watch_registration: WatchRegistration,
@@ -97,10 +97,12 @@ impl CodexThread {
     pub(crate) fn new(
         codex: Codex,
         rollout_path: Option<PathBuf>,
+        session_source: SessionSource,
         watch_registration: WatchRegistration,
     ) -> Self {
         Self {
             codex,
+            session_source,
             rollout_path,
             out_of_band_elicitation_count: Mutex::new(0),
             _watch_registration: watch_registration,
@@ -115,6 +117,11 @@ impl CodexThread {
         self.codex.shutdown_and_wait().await
     }
 
+    /// Wait until the underlying session loop has terminated.
+    pub async fn wait_until_terminated(&self) {
+        self.codex.session_loop_termination.clone().await;
+    }
+
     pub async fn apply_goal_resume_runtime_effects(&self) -> anyhow::Result<()> {
         self.codex
             .session
@@ -268,10 +275,6 @@ impl CodexThread {
         self.codex.agent_status.clone()
     }
 
-    pub(crate) async fn total_token_usage(&self) -> Option<TokenUsage> {
-        self.codex.session.total_token_usage().await
-    }
-
     /// Returns the complete token usage snapshot currently cached for this thread.
     ///
     /// This accessor is intentionally narrower than direct session access: it lets