diff --git a/codex-rs/core/src/exec_env.rs b/codex-rs/core/src/exec_env.rs
index 91bf97ef0c..4b4fee7bd2 100644
--- a/codex-rs/core/src/exec_env.rs
+++ b/codex-rs/core/src/exec_env.rs
@@ -4,6 +4,8 @@ use crate::config::types::ShellEnvironmentPolicyInherit;
 use std::collections::HashMap;
 use std::collections::HashSet;
 
+pub const CODEX_SESSION_ID_ENV_VAR: &str = "CODEX_SESSION_ID";
+
 /// Construct an environment map based on the rules in the specified policy. The
 /// resulting map can be passed directly to `Command::envs()` after calling
 /// `env_clear()` to ensure no unintended variables are leaked to the spawned
diff --git a/codex-rs/core/src/tools/handlers/shell.rs b/codex-rs/core/src/tools/handlers/shell.rs
index b59c0140d1..f6e315282e 100644
--- a/codex-rs/core/src/tools/handlers/shell.rs
+++ b/codex-rs/core/src/tools/handlers/shell.rs
@@ -5,6 +5,7 @@ use std::sync::Arc;
 
 use crate::codex::TurnContext;
 use crate::exec::ExecParams;
+use crate::exec_env::CODEX_SESSION_ID_ENV_VAR;
 use crate::exec_env::create_env;
 use crate::exec_policy::ExecApprovalRequest;
 use crate::function_tool::FunctionCallError;
@@ -238,6 +239,10 @@ impl ShellHandler {
         if !dependency_env.is_empty() {
             exec_params.env.extend(dependency_env);
         }
+        exec_params
+            .env
+            .entry(CODEX_SESSION_ID_ENV_VAR.to_string())
+            .or_insert_with(|| session.conversation_id.to_string());
 
         // Approval policy guard for explicit escalation in non-OnRequest modes.
         if exec_params