fix: Scope ExecSessionManager to Session instead of using global singleton (#2664)

The `SessionManager` in `exec_command` owns a number of
`ExecCommandSession` objects where `ExecCommandSession` has a
non-trivial implementation of `Drop`, so we want to be able to drop an
individual `SessionManager` to help ensure things get cleaned up in a
timely fashion. To that end, we should have one `SessionManager` per
session rather than one global one for the lifetime of the CLI process.

codex-rs/core/src/codex.rs

@@ -55,7 +55,7 @@ use crate::exec::StreamOutput;
 use crate::exec::process_exec_tool_call;
 use crate::exec_command::EXEC_COMMAND_TOOL_NAME;
 use crate::exec_command::ExecCommandParams;
-use crate::exec_command::SESSION_MANAGER;
+use crate::exec_command::ExecSessionManager;
 use crate::exec_command::WRITE_STDIN_TOOL_NAME;
 use crate::exec_command::WriteStdinParams;
 use crate::exec_env::create_env;
@@ -269,6 +269,7 @@ pub(crate) struct Session {
 
     /// Manager for external MCP servers/tools.
     mcp_connection_manager: McpConnectionManager,
+    session_manager: ExecSessionManager,
 
     /// External notifier command (will be passed as args to exec()). When
     /// `None` this feature is disabled.
@@ -528,6 +529,7 @@ impl Session {
             session_id,
             tx_event: tx_event.clone(),
             mcp_connection_manager,
+            session_manager: ExecSessionManager::default(),
             notify,
             state: Mutex::new(state),
             rollout: Mutex::new(rollout_recorder),
@@ -2112,7 +2114,8 @@ async fn handle_function_call(
                     };
                 }
             };
-            let result = SESSION_MANAGER
+            let result = sess
+                .session_manager
                 .handle_exec_command_request(exec_params)
                 .await;
             let function_call_output = crate::exec_command::result_into_payload(result);
@@ -2134,7 +2137,8 @@ async fn handle_function_call(
                     };
                 }
             };
-            let result = SESSION_MANAGER
+            let result = sess
+                .session_manager
                 .handle_write_stdin_request(write_stdin_params)
                 .await;
             let function_call_output: FunctionCallOutputPayload =

codex-rs/core/src/exec_command/mod.rs

@@ -10,5 +10,5 @@ pub use responses_api::EXEC_COMMAND_TOOL_NAME;
 pub use responses_api::WRITE_STDIN_TOOL_NAME;
 pub use responses_api::create_exec_command_tool_for_responses_api;
 pub use responses_api::create_write_stdin_tool_for_responses_api;
-pub use session_manager::SESSION_MANAGER;
+pub use session_manager::SessionManager as ExecSessionManager;
 pub use session_manager::result_into_payload;

codex-rs/core/src/exec_command/session_manager.rs

@@ -2,7 +2,6 @@ use std::collections::HashMap;
 use std::io::ErrorKind;
 use std::io::Read;
 use std::sync::Arc;
-use std::sync::LazyLock;
 use std::sync::Mutex as StdMutex;
 use std::sync::atomic::AtomicU32;
 
@@ -22,8 +21,6 @@ use crate::exec_command::exec_command_session::ExecCommandSession;
 use crate::exec_command::session_id::SessionId;
 use codex_protocol::models::FunctionCallOutputPayload;
 
-pub static SESSION_MANAGER: LazyLock<SessionManager> = LazyLock::new(SessionManager::default);
-
 #[derive(Debug, Default)]
 pub struct SessionManager {
     next_session_id: AtomicU32,