Expose the session ID to shell commands (#37848)

## What changed

- Set `CODEX_SESSION_ID` to the shared root-session ID for shell tool calls,
  unified exec processes, and user shell commands.
- Preserve `CODEX_SESSION_ID` when restoring a shell snapshot, alongside the
  existing runtime-owned environment variables.

GitOrigin-RevId: 5228867d25507105c7edf11607a8298958c3b917

codex-rs/core/src/exec_env.rs

@@ -1,6 +1,7 @@
 pub use codex_apply_patch::CODEX_APPLY_PATCH_PRESERVE_LINE_ENDINGS_ENV_VAR;
 use codex_features::Feature;
 use codex_features::Features;
+use codex_protocol::SessionId;
 use codex_protocol::ThreadId;
 #[cfg(test)]
 use codex_protocol::config_types::EnvironmentVariablePattern;
@@ -9,6 +10,7 @@ use codex_protocol::models::ActivePermissionProfile;
 use codex_protocol::shell_environment;
 use std::collections::HashMap;
 
+pub use codex_protocol::shell_environment::CODEX_SESSION_ID_ENV_VAR;
 pub use codex_protocol::shell_environment::CODEX_THREAD_ID_ENV_VAR;
 
 /// Informational name of the active permission profile. Child processes can
@@ -33,6 +35,11 @@ pub fn create_env(
     shell_environment::create_env(policy, thread_id.as_deref())
 }
 
+/// Exposes the shared root-session identity to model-reachable shell commands.
+pub(crate) fn inject_session_id_env(env: &mut HashMap<String, String>, session_id: SessionId) {
+    env.insert(CODEX_SESSION_ID_ENV_VAR.to_string(), session_id.to_string());
+}
+
 /// Injects the selected named permission profile into a shell tool's environment.
 ///
 /// This is applied after the shell environment policy so the runtime-selected

codex-rs/core/src/tasks/user_shell.rs

@@ -15,6 +15,7 @@ use crate::exec::StdoutStream;
 use crate::exec::execute_exec_request;
 use crate::exec_env::create_env;
 use crate::exec_env::inject_apply_patch_env;
+use crate::exec_env::inject_session_id_env;
 use crate::sandboxing::ExecRequest;
 use crate::session::TurnInput;
 use crate::session::turn_context::TurnContext;
@@ -160,6 +161,7 @@ pub(crate) async fn execute_user_shell_command(
         &turn_context.config.permissions.shell_environment_policy,
         Some(session.thread_id),
     );
+    inject_session_id_env(&mut exec_env_map, session.session_id());
     inject_apply_patch_env(&mut exec_env_map, &turn_context.config.features);
     if exec_env_map.contains_key(PROXY_ACTIVE_ENV_KEY) {
         strip_managed_proxy_env(&mut exec_env_map);

codex-rs/core/src/tools/handlers/shell/shell_command.rs

@@ -8,6 +8,7 @@ use crate::exec::ExecParams;
 use crate::exec_env::create_env;
 use crate::exec_env::inject_apply_patch_env;
 use crate::exec_env::inject_permission_profile_env;
+use crate::exec_env::inject_session_id_env;
 use crate::function_tool::FunctionCallError;
 use crate::maybe_emit_implicit_skill_invocation;
 use crate::session::turn_context::TurnContext;
@@ -106,6 +107,7 @@ impl ShellCommandHandler {
             &turn_context.config.permissions.shell_environment_policy,
             Some(session.thread_id),
         );
+        inject_session_id_env(&mut env, session.session_id());
         inject_apply_patch_env(&mut env, &turn_context.config.features);
         let active_permission_profile = turn_environment.active_permission_profile();
         inject_permission_profile_env(&mut env, active_permission_profile.as_ref());

codex-rs/core/src/tools/handlers/shell_tests.rs

@@ -9,6 +9,7 @@ use crate::config::PermissionProfileSnapshot;
 use crate::exec_env::CODEX_PERMISSION_PROFILE_ENV_VAR;
 use crate::exec_env::create_env;
 use crate::exec_env::inject_permission_profile_env;
+use crate::exec_env::inject_session_id_env;
 use crate::sandboxing::SandboxPermissions;
 use crate::session::step_context::StepContext;
 use crate::session::tests::make_session_and_context;
@@ -125,6 +126,7 @@ async fn shell_command_handler_to_exec_params_uses_selected_environment() {
         &turn_context.config.permissions.shell_environment_policy,
         Some(session.thread_id),
     );
+    inject_session_id_env(&mut expected_env, session.session_id());
     inject_permission_profile_env(&mut expected_env, Some(&active_permission_profile));
 
     let params = ShellCommandToolCallParams {

codex-rs/core/src/tools/runtimes/mod.rs

@@ -5,6 +5,7 @@ Concrete ToolRuntime implementations for specific tools. Each runtime stays
 small and focused and reuses the orchestrator for approvals + sandbox + retry.
 */
 use crate::exec_env::CODEX_PERMISSION_PROFILE_ENV_VAR;
+use crate::exec_env::CODEX_SESSION_ID_ENV_VAR;
 use crate::exec_env::CODEX_THREAD_ID_ENV_VAR;
 use crate::sandboxing::SandboxPermissions;
 use crate::shell::Shell;
@@ -269,6 +270,7 @@ pub(crate) fn maybe_wrap_shell_lc_with_snapshot(
         .collect::<String>();
     let mut override_env = explicit_env_overrides.clone();
     for key in [
+        CODEX_SESSION_ID_ENV_VAR,
         CODEX_THREAD_ID_ENV_VAR,
         CODEX_PERMISSION_PROFILE_ENV_VAR,
         CODEX_APPLY_PATCH_PRESERVE_LINE_ENDINGS_ENV_VAR,

codex-rs/core/src/unified_exec/process_manager.rs

@@ -18,6 +18,7 @@ use crate::exec_env::CODEX_THREAD_ID_ENV_VAR;
 use crate::exec_env::create_env;
 use crate::exec_env::inject_apply_patch_env;
 use crate::exec_env::inject_permission_profile_env;
+use crate::exec_env::inject_session_id_env;
 use crate::exec_policy::ExecApprovalRequest;
 use crate::sandboxing::ExecOptions;
 use crate::sandboxing::ExecRequest;
@@ -1160,6 +1161,7 @@ impl UnifiedExecProcessManager {
             CODEX_THREAD_ID_ENV_VAR.to_string(),
             context.session.thread_id.to_string(),
         );
+        inject_session_id_env(&mut env, context.session.session_id());
         inject_apply_patch_env(&mut env, &turn.config.features);
         let active_permission_profile = request.turn_environment.active_permission_profile();
         inject_permission_profile_env(&mut env, active_permission_profile.as_ref());

codex-rs/protocol/src/shell_environment.rs

@@ -3,6 +3,7 @@ use crate::config_types::ShellEnvironmentPolicy;
 use crate::config_types::ShellEnvironmentPolicyInherit;
 use std::collections::HashMap;
 
+pub const CODEX_SESSION_ID_ENV_VAR: &str = "CODEX_SESSION_ID";
 pub const CODEX_THREAD_ID_ENV_VAR: &str = "CODEX_THREAD_ID";
 pub const OPENAI_FEDERATION_RULE_ID_ENV_VAR: &str = "OPENAI_FEDERATION_RULE_ID";
 pub const OPENAI_IDENTITY_TOKEN_FILE_ENV_VAR: &str = "OPENAI_IDENTITY_TOKEN_FILE";