Defer executor readiness when prewarming a selected project (#60309)

## What changed

Set `deferred_environment` to `true` in cloud thread prewarm requests when a project is selected. Omit the field for default thread prewarming.

## Testing

Update the prewarm request encoding test to verify that only requests with a selected project include the deferred readiness flag.

GitOrigin-RevId: e10a646ebde9cc3acbdb01b304af0f73ecc1dbeb

codex-rs/cloud-client/src/client_tests.rs

@@ -232,7 +232,7 @@ async fn activation_preserves_native_settings_and_thread_metadata() {
 }
 
 #[tokio::test]
-async fn prewarm_encodes_blank_and_project_managed_environments() {
+async fn prewarm_defers_readiness_only_for_selected_projects() {
     let mut fixture = fixture_responses(vec![
         response(vec![frame(&[])], tonic::Status::ok("")),
         response(vec![frame(&[])], tonic::Status::ok("")),
@@ -274,7 +274,7 @@ async fn prewarm_encodes_blank_and_project_managed_environments() {
         b"git@github.com:acme/app.git",
         b"\x0a\x21\x2a\x1f",
         b"https://github.com/acme/lib.git",
-        b"\x12\x03App",
+        b"\x12\x03App\xe8\x01\x01",
     ]
     .concat();
     assert_request(&mut fixture, "Prewarm", &expected).await;

codex-rs/cloud-client/src/prewarm.rs

@@ -37,13 +37,14 @@ impl Client {
             .await
     }
 
-    /// Prewarm a coding thread with an optional project checkout.
+    /// Prewarm a coding thread, deferring executor readiness for a selected project checkout.
     pub async fn prewarm_thread(
         &self,
         model: Option<String>,
         model_provider: Option<String>,
         project: Option<ProjectEnvironment>,
     ) -> Result<crate::ThreadActivation, Error> {
+        let deferred_environment = project.is_some().then_some(true);
         let managed = match project {
             Some(ProjectEnvironment {
                 name,
@@ -71,6 +72,7 @@ impl Client {
                 wire::PrewarmRequest {
                     model,
                     model_provider,
+                    deferred_environment,
                     environments: Some(wire::EnvironmentList {
                         values: vec![wire::EnvironmentSelection {
                             managed: Some(managed),
@@ -116,6 +118,8 @@ mod wire {
         pub model: Option<String>,
         #[prost(string, optional, tag = "16")]
         pub model_provider: Option<String>,
+        #[prost(bool, optional, tag = "29")]
+        pub deferred_environment: Option<bool>,
     }
     #[derive(Clone, Message)]
     pub(super) struct EnvironmentList {