Inherit ready step environments when spawning agents (#35895)

## Why

With deferred execution, an environment can become ready before a later step
spawns a sub-agent. The child must inherit the environment selections available
to that step.

## What changed

- Use the current step context's environment selections when spawning agents in
  both multi-agent implementations.
- Add coverage that waits for a remote environment to become ready, spawns an
  agent, and verifies that the child receives both remote and local selections.

GitOrigin-RevId: 97c37d541342bbefc9217bf341a19ebdfead2c76

codex-rs/core/src/tools/handlers/multi_agents/spawn.rs

@@ -46,11 +46,12 @@ async fn handle_spawn_agent(
 ) -> Result<SpawnAgentResult, FunctionCallError> {
     let ToolInvocation {
         session,
-        turn,
+        step_context,
         payload,
         call_id,
         ..
     } = invocation;
+    let turn = &step_context.turn;
     let arguments = function_arguments(payload)?;
     let args: SpawnAgentArgs = parse_arguments(&arguments)?;
     let role_name = args
@@ -70,7 +71,7 @@ async fn handle_spawn_agent(
     }
     session
         .emit_turn_item_started(
-            &turn,
+            turn,
             &TurnItem::CollabAgentToolCall(CollabAgentToolCallItem {
                 id: call_id.clone(),
                 tool: CollabAgentTool::SpawnAgent,
@@ -128,7 +129,7 @@ async fn handle_spawn_agent(
             fork_mode: args.fork_context.then_some(SpawnAgentForkMode::FullHistory),
             parent_thread_id: Some(session.thread_id),
             parent_turn_id: Some(turn.sub_id.clone()),
-            environments: Some(turn.environments.to_selections()),
+            environments: Some(step_context.environments.to_selections()),
         },
     ))
     .await
@@ -188,7 +189,7 @@ async fn handle_spawn_agent(
         .unwrap_or_default();
     session
         .emit_turn_item_completed(
-            &turn,
+            turn,
             TurnItem::CollabAgentToolCall(CollabAgentToolCallItem {
                 id: call_id,
                 tool: CollabAgentTool::SpawnAgent,

codex-rs/core/src/tools/handlers/multi_agents_v2/spawn.rs

@@ -41,12 +41,13 @@ async fn handle_spawn_agent(
 ) -> Result<SpawnAgentResult, FunctionCallError> {
     let ToolInvocation {
         session,
-        turn,
+        step_context,
         payload,
         call_id,
         source,
         ..
     } = invocation;
+    let turn = &step_context.turn;
     let arguments = function_arguments(payload)?;
     let args: SpawnAgentArgs = parse_arguments(&arguments)?;
     let fork_mode = args.fork_mode()?;
@@ -126,7 +127,7 @@ async fn handle_spawn_agent(
                     fork_mode,
                     parent_thread_id: Some(session.thread_id),
                     parent_turn_id: Some(turn.sub_id.clone()),
-                    environments: Some(turn.environments.to_selections()),
+                    environments: Some(step_context.environments.to_selections()),
                 },
             ),
     )
@@ -144,7 +145,7 @@ async fn handle_spawn_agent(
         .or(spawned_agent.metadata.agent_nickname);
     emit_sub_agent_activity(
         &session,
-        &turn,
+        turn,
         SubAgentActivityItem {
             id: call_id,
             agent_thread_id: new_thread_id,