diff --git a/codex-rs/core/src/tools/code_mode/execute_handler.rs b/codex-rs/core/src/tools/code_mode/execute_handler.rs
index 1c65161fd..56a13ae47 100644
--- a/codex-rs/core/src/tools/code_mode/execute_handler.rs
+++ b/codex-rs/core/src/tools/code_mode/execute_handler.rs
@@ -32,7 +32,7 @@ impl CodeModeExecuteHandler {
         let stored_values = service.stored_values().await;
         let source =
             build_source(&code, &enabled_tools).map_err(FunctionCallError::RespondToModel)?;
-        let session_id = service.allocate_session_id().await;
+        let cell_id = service.allocate_cell_id().await;
         let request_id = service.allocate_request_id().await;
         let process_slot = service
             .ensure_started()
@@ -41,7 +41,7 @@ impl CodeModeExecuteHandler {
         let started_at = std::time::Instant::now();
         let message = HostToNodeMessage::Start {
             request_id: request_id.clone(),
-            session_id,
+            cell_id: cell_id.clone(),
             default_yield_time_ms: super::DEFAULT_EXEC_YIELD_TIME_MS,
             enabled_tools,
             stored_values,
@@ -62,7 +62,7 @@ impl CodeModeExecuteHandler {
                 Ok(message) => message,
                 Err(error) => return Err(FunctionCallError::RespondToModel(error)),
             };
-            handle_node_message(&exec, session_id, message, None, started_at).await
+            handle_node_message(&exec, cell_id, message, None, started_at).await
         };
         match result {
             Ok(CodeModeSessionProgress::Finished(output))
diff --git a/codex-rs/core/src/tools/code_mode/mod.rs b/codex-rs/core/src/tools/code_mode/mod.rs
index ce72f7ba1..9a92a2486 100644
--- a/codex-rs/core/src/tools/code_mode/mod.rs
+++ b/codex-rs/core/src/tools/code_mode/mod.rs
@@ -57,7 +57,7 @@ enum CodeModeSessionProgress {
 enum CodeModeExecutionStatus {
     Completed,
     Failed,
-    Running(i32),
+    Running(String),
     Terminated,
 }
 
@@ -79,7 +79,7 @@ pub(crate) fn wait_tool_description() -> &'static str {
 
 async fn handle_node_message(
     exec: &ExecContext,
-    session_id: i32,
+    cell_id: String,
     message: protocol::NodeToHostMessage,
     poll_max_output_tokens: Option<Option<usize>>,
     started_at: std::time::Instant,
@@ -91,7 +91,7 @@ async fn handle_node_message(
             delta_items = truncate_code_mode_result(delta_items, poll_max_output_tokens.flatten());
             prepend_script_status(
                 &mut delta_items,
-                CodeModeExecutionStatus::Running(session_id),
+                CodeModeExecutionStatus::Running(cell_id),
                 started_at.elapsed(),
             );
             Ok(CodeModeSessionProgress::Yielded {
@@ -161,8 +161,8 @@ fn prepend_script_status(
         match status {
             CodeModeExecutionStatus::Completed => "Script completed".to_string(),
             CodeModeExecutionStatus::Failed => "Script failed".to_string(),
-            CodeModeExecutionStatus::Running(session_id) => {
-                format!("Script running with session ID {session_id}")
+            CodeModeExecutionStatus::Running(cell_id) => {
+                format!("Script running with cell ID {cell_id}")
             }
             CodeModeExecutionStatus::Terminated => "Script terminated".to_string(),
         }
diff --git a/codex-rs/core/src/tools/code_mode/protocol.rs b/codex-rs/core/src/tools/code_mode/protocol.rs
index 6cd50d3f9..44757f858 100644
--- a/codex-rs/core/src/tools/code_mode/protocol.rs
+++ b/codex-rs/core/src/tools/code_mode/protocol.rs
@@ -41,7 +41,7 @@ pub(super) struct CodeModeToolCall {
 pub(super) enum HostToNodeMessage {
     Start {
         request_id: String,
-        session_id: i32,
+        cell_id: String,
         default_yield_time_ms: u64,
         enabled_tools: Vec<EnabledTool>,
         stored_values: HashMap<String, JsonValue>,
@@ -49,12 +49,12 @@ pub(super) enum HostToNodeMessage {
     },
     Poll {
         request_id: String,
-        session_id: i32,
+        cell_id: String,
         yield_time_ms: u64,
     },
     Terminate {
         request_id: String,
-        session_id: i32,
+        cell_id: String,
     },
     Response {
         request_id: String,
diff --git a/codex-rs/core/src/tools/code_mode/runner.cjs b/codex-rs/core/src/tools/code_mode/runner.cjs
index 7668eb2ef..b2002a2b7 100644
--- a/codex-rs/core/src/tools/code_mode/runner.cjs
+++ b/codex-rs/core/src/tools/code_mode/runner.cjs
@@ -486,7 +486,7 @@ function createProtocol() {
     }
 
     if (message.type === 'poll') {
-      const session = sessions.get(message.session_id);
+      const session = sessions.get(message.cell_id);
       if (session) {
         session.request_id = String(message.request_id);
         if (session.pending_result) {
@@ -500,7 +500,7 @@ function createProtocol() {
           request_id: message.request_id,
           content_items: [],
           stored_values: {},
-          error_text: `exec session ${message.session_id} not found`,
+          error_text: `exec cell ${message.cell_id} not found`,
           max_output_tokens_per_exec_call: DEFAULT_MAX_OUTPUT_TOKENS_PER_EXEC_CALL,
         });
       }
@@ -508,7 +508,7 @@ function createProtocol() {
     }
 
     if (message.type === 'terminate') {
-      const session = sessions.get(message.session_id);
+      const session = sessions.get(message.cell_id);
       if (session) {
         session.request_id = String(message.request_id);
         void terminateSession(protocol, sessions, session);
@@ -518,7 +518,7 @@ function createProtocol() {
           request_id: message.request_id,
           content_items: [],
           stored_values: {},
-          error_text: `exec session ${message.session_id} not found`,
+          error_text: `exec cell ${message.cell_id} not found`,
           max_output_tokens_per_exec_call: DEFAULT_MAX_OUTPUT_TOKENS_PER_EXEC_CALL,
         });
       }
@@ -591,7 +591,7 @@ function startSession(protocol, sessions, start) {
     completed: false,
     content_items: [],
     default_yield_time_ms: normalizeYieldTime(start.default_yield_time_ms),
-    id: start.session_id,
+    id: start.cell_id,
     initial_yield_timer: null,
     initial_yield_triggered: false,
     max_output_tokens_per_exec_call: DEFAULT_MAX_OUTPUT_TOKENS_PER_EXEC_CALL,
diff --git a/codex-rs/core/src/tools/code_mode/service.rs b/codex-rs/core/src/tools/code_mode/service.rs
index 0df1f88dd..52b519651 100644
--- a/codex-rs/core/src/tools/code_mode/service.rs
+++ b/codex-rs/core/src/tools/code_mode/service.rs
@@ -24,7 +24,7 @@ pub(crate) struct CodeModeService {
     js_repl_node_path: Option<PathBuf>,
     stored_values: Mutex<HashMap<String, JsonValue>>,
     process: Arc<Mutex<Option<CodeModeProcess>>>,
-    next_session_id: Mutex<i32>,
+    next_cell_id: Mutex<u64>,
 }
 
 impl CodeModeService {
@@ -33,7 +33,7 @@ impl CodeModeService {
             js_repl_node_path,
             stored_values: Mutex::new(HashMap::new()),
             process: Arc::new(Mutex::new(None)),
-            next_session_id: Mutex::new(1),
+            next_cell_id: Mutex::new(1),
         }
     }
 
@@ -95,11 +95,11 @@ impl CodeModeService {
         Some(process.worker(exec, tool_runtime))
     }
 
-    pub(crate) async fn allocate_session_id(&self) -> i32 {
-        let mut next_session_id = self.next_session_id.lock().await;
-        let session_id = *next_session_id;
-        *next_session_id = next_session_id.saturating_add(1);
-        session_id
+    pub(crate) async fn allocate_cell_id(&self) -> String {
+        let mut next_cell_id = self.next_cell_id.lock().await;
+        let cell_id = *next_cell_id;
+        *next_cell_id = next_cell_id.saturating_add(1);
+        cell_id.to_string()
     }
 
     pub(crate) async fn allocate_request_id(&self) -> String {
diff --git a/codex-rs/core/src/tools/code_mode/wait_description.md b/codex-rs/core/src/tools/code_mode/wait_description.md
index 77ec11295..5780b007b 100644
--- a/codex-rs/core/src/tools/code_mode/wait_description.md
+++ b/codex-rs/core/src/tools/code_mode/wait_description.md
@@ -1,8 +1,8 @@
-- Use `exec_wait` only after `exec` returns `Script running with session ID ...`.
-- `session_id` identifies the running `exec` session to resume.
+- Use `exec_wait` only after `exec` returns `Script running with cell ID ...`.
+- `cell_id` identifies the running `exec` cell to resume.
 - `yield_time_ms` controls how long to wait for more output before yielding again. If omitted, `exec_wait` uses its default wait timeout.
 - `max_tokens` limits how much new output this wait call returns.
-- `terminate: true` stops the running session instead of waiting for more output.
-- `exec_wait` returns only the new output since the last yield, or the final completion or termination result for that session.
-- If the session is still running, `exec_wait` may yield again with the same `session_id`.
-- If the session has already finished, `exec_wait` returns the completed result and closes the session.
+- `terminate: true` stops the running cell instead of waiting for more output.
+- `exec_wait` returns only the new output since the last yield, or the final completion or termination result for that cell.
+- If the cell is still running, `exec_wait` may yield again with the same `cell_id`.
+- If the cell has already finished, `exec_wait` returns the completed result and closes the cell.
diff --git a/codex-rs/core/src/tools/code_mode/wait_handler.rs b/codex-rs/core/src/tools/code_mode/wait_handler.rs
index fe9fe5e5b..caaf8c8c4 100644
--- a/codex-rs/core/src/tools/code_mode/wait_handler.rs
+++ b/codex-rs/core/src/tools/code_mode/wait_handler.rs
@@ -20,7 +20,7 @@ pub struct CodeModeWaitHandler;
 
 #[derive(Debug, Deserialize)]
 struct ExecWaitArgs {
-    session_id: i32,
+    cell_id: String,
     #[serde(default = "default_wait_yield_time_ms")]
     yield_time_ms: u64,
     #[serde(default)]
@@ -73,12 +73,12 @@ impl ToolHandler for CodeModeWaitHandler {
                 let message = if args.terminate {
                     HostToNodeMessage::Terminate {
                         request_id: request_id.clone(),
-                        session_id: args.session_id,
+                        cell_id: args.cell_id.clone(),
                     }
                 } else {
                     HostToNodeMessage::Poll {
                         request_id: request_id.clone(),
-                        session_id: args.session_id,
+                        cell_id: args.cell_id.clone(),
                         yield_time_ms: args.yield_time_ms,
                     }
                 };
@@ -111,7 +111,7 @@ impl ToolHandler for CodeModeWaitHandler {
                     };
                     handle_node_message(
                         &exec,
-                        args.session_id,
+                        args.cell_id,
                         message,
                         Some(args.max_tokens),
                         started_at,
diff --git a/codex-rs/core/src/tools/spec.rs b/codex-rs/core/src/tools/spec.rs
index a31fe612f..9fed64097 100644
--- a/codex-rs/core/src/tools/spec.rs
+++ b/codex-rs/core/src/tools/spec.rs
@@ -622,9 +622,9 @@ fn create_write_stdin_tool() -> ToolSpec {
 fn create_exec_wait_tool() -> ToolSpec {
     let properties = BTreeMap::from([
         (
-            "session_id".to_string(),
-            JsonSchema::Number {
-                description: Some("Identifier of the running exec session.".to_string()),
+            "cell_id".to_string(),
+            JsonSchema::String {
+                description: Some("Identifier of the running exec cell.".to_string()),
             },
         ),
         (
@@ -647,7 +647,7 @@ fn create_exec_wait_tool() -> ToolSpec {
         (
             "terminate".to_string(),
             JsonSchema::Boolean {
-                description: Some("Whether to terminate the running exec session.".to_string()),
+                description: Some("Whether to terminate the running exec cell.".to_string()),
             },
         ),
     ]);
@@ -655,13 +655,13 @@ fn create_exec_wait_tool() -> ToolSpec {
     ToolSpec::Function(ResponsesApiTool {
         name: WAIT_TOOL_NAME.to_string(),
         description: format!(
-            "Waits on a yielded `{PUBLIC_TOOL_NAME}` session and returns new output or completion.\n{}",
+            "Waits on a yielded `{PUBLIC_TOOL_NAME}` cell and returns new output or completion.\n{}",
             code_mode_wait_tool_description().trim()
         ),
         strict: false,
         parameters: JsonSchema::Object {
             properties,
-            required: Some(vec!["session_id".to_string()]),
+            required: Some(vec!["cell_id".to_string()]),
             additional_properties: Some(false.into()),
         },
         output_schema: None,
diff --git a/codex-rs/core/tests/suite/code_mode.rs b/codex-rs/core/tests/suite/code_mode.rs
index 6baa50ada..a427a5bc9 100644
--- a/codex-rs/core/tests/suite/code_mode.rs
+++ b/codex-rs/core/tests/suite/code_mode.rs
@@ -52,12 +52,11 @@ fn text_item(items: &[Value], index: usize) -> &str {
         .expect("content item should be input_text")
 }
 
-fn extract_running_session_id(text: &str) -> i32 {
-    text.strip_prefix("Script running with session ID ")
+fn extract_running_cell_id(text: &str) -> String {
+    text.strip_prefix("Script running with cell ID ")
         .and_then(|rest| rest.split('\n').next())
-        .expect("running header should contain a session ID")
-        .parse()
-        .expect("session ID should parse as i32")
+        .expect("running header should contain a cell ID")
+        .to_string()
 }
 
 fn wait_for_file_source(path: &Path) -> Result<String> {
@@ -422,12 +421,12 @@ output_text("phase 3");
     assert_regex_match(
         concat!(
             r"(?s)\A",
-            r"Script running with session ID \d+\nWall time \d+\.\d seconds\nOutput:\n\z"
+            r"Script running with cell ID \d+\nWall time \d+\.\d seconds\nOutput:\n\z"
         ),
         text_item(&first_items, 0),
     );
     assert_eq!(text_item(&first_items, 1), "phase 1");
-    let session_id = extract_running_session_id(text_item(&first_items, 0));
+    let cell_id = extract_running_cell_id(text_item(&first_items, 0));
 
     responses::mount_sse_once(
         &server,
@@ -437,7 +436,7 @@ output_text("phase 3");
                 "call-2",
                 "exec_wait",
                 &serde_json::to_string(&serde_json::json!({
-                    "session_id": session_id,
+                    "cell_id": cell_id.clone(),
                     "yield_time_ms": 1_000,
                 }))?,
             ),
@@ -463,13 +462,13 @@ output_text("phase 3");
     assert_regex_match(
         concat!(
             r"(?s)\A",
-            r"Script running with session ID \d+\nWall time \d+\.\d seconds\nOutput:\n\z"
+            r"Script running with cell ID \d+\nWall time \d+\.\d seconds\nOutput:\n\z"
         ),
         text_item(&second_items, 0),
     );
     assert_eq!(
-        extract_running_session_id(text_item(&second_items, 0)),
-        session_id
+        extract_running_cell_id(text_item(&second_items, 0)),
+        cell_id
     );
     assert_eq!(text_item(&second_items, 1), "phase 2");
 
@@ -481,7 +480,7 @@ output_text("phase 3");
                 "call-3",
                 "exec_wait",
                 &serde_json::to_string(&serde_json::json!({
-                    "session_id": session_id,
+                    "cell_id": cell_id.clone(),
                     "yield_time_ms": 1_000,
                 }))?,
             ),
@@ -565,12 +564,12 @@ while (true) {}
     assert_regex_match(
         concat!(
             r"(?s)\A",
-            r"Script running with session ID \d+\nWall time \d+\.\d seconds\nOutput:\n\z"
+            r"Script running with cell ID \d+\nWall time \d+\.\d seconds\nOutput:\n\z"
         ),
         text_item(&first_items, 0),
     );
     assert_eq!(text_item(&first_items, 1), "phase 1");
-    let session_id = extract_running_session_id(text_item(&first_items, 0));
+    let cell_id = extract_running_cell_id(text_item(&first_items, 0));
 
     responses::mount_sse_once(
         &server,
@@ -580,7 +579,7 @@ while (true) {}
                 "call-2",
                 "exec_wait",
                 &serde_json::to_string(&serde_json::json!({
-                    "session_id": session_id,
+                    "cell_id": cell_id.clone(),
                     "terminate": true,
                 }))?,
             ),
@@ -674,7 +673,7 @@ output_text("session b done");
     let first_request = first_completion.single_request();
     let first_items = custom_tool_output_items(&first_request, "call-1");
     assert_eq!(first_items.len(), 2);
-    let session_a_id = extract_running_session_id(text_item(&first_items, 0));
+    let session_a_id = extract_running_cell_id(text_item(&first_items, 0));
     assert_eq!(text_item(&first_items, 1), "session a start");
 
     responses::mount_sse_once(
@@ -700,7 +699,7 @@ output_text("session b done");
     let second_request = second_completion.single_request();
     let second_items = custom_tool_output_items(&second_request, "call-2");
     assert_eq!(second_items.len(), 2);
-    let session_b_id = extract_running_session_id(text_item(&second_items, 0));
+    let session_b_id = extract_running_cell_id(text_item(&second_items, 0));
     assert_eq!(text_item(&second_items, 1), "session b start");
     assert_ne!(session_a_id, session_b_id);
 
@@ -713,7 +712,7 @@ output_text("session b done");
                 "call-3",
                 "exec_wait",
                 &serde_json::to_string(&serde_json::json!({
-                    "session_id": session_a_id,
+                    "cell_id": session_a_id.clone(),
                     "yield_time_ms": 1_000,
                 }))?,
             ),
@@ -753,7 +752,7 @@ output_text("session b done");
                 "call-4",
                 "exec_wait",
                 &serde_json::to_string(&serde_json::json!({
-                    "session_id": session_b_id,
+                    "cell_id": session_b_id.clone(),
                     "yield_time_ms": 1_000,
                 }))?,
             ),
@@ -835,7 +834,7 @@ output_text("phase 2");
     let first_request = first_completion.single_request();
     let first_items = custom_tool_output_items(&first_request, "call-1");
     assert_eq!(first_items.len(), 2);
-    let session_id = extract_running_session_id(text_item(&first_items, 0));
+    let cell_id = extract_running_cell_id(text_item(&first_items, 0));
     assert_eq!(text_item(&first_items, 1), "phase 1");
 
     responses::mount_sse_once(
@@ -846,7 +845,7 @@ output_text("phase 2");
                 "call-2",
                 "exec_wait",
                 &serde_json::to_string(&serde_json::json!({
-                    "session_id": session_id,
+                    "cell_id": cell_id.clone(),
                     "terminate": true,
                 }))?,
             ),
@@ -937,7 +936,7 @@ async fn code_mode_exec_wait_returns_error_for_unknown_session() -> Result<()> {
                 "call-1",
                 "exec_wait",
                 &serde_json::to_string(&serde_json::json!({
-                    "session_id": 999_999,
+                    "cell_id": "999999",
                     "yield_time_ms": 1_000,
                 }))?,
             ),
@@ -954,7 +953,7 @@ async fn code_mode_exec_wait_returns_error_for_unknown_session() -> Result<()> {
     )
     .await;
 
-    test.submit_turn("wait on an unknown exec session").await?;
+    test.submit_turn("wait on an unknown exec cell").await?;
 
     let request = completion.single_request();
     let (_, success) = request
@@ -973,7 +972,7 @@ async fn code_mode_exec_wait_returns_error_for_unknown_session() -> Result<()> {
     );
     assert_eq!(
         text_item(&items, 1),
-        "Script error:\nexec session 999999 not found"
+        "Script error:\nexec cell 999999 not found"
     );
 
     Ok(())
@@ -1046,7 +1045,7 @@ output_text("session b done");
     let first_request = first_completion.single_request();
     let first_items = custom_tool_output_items(&first_request, "call-1");
     assert_eq!(first_items.len(), 2);
-    let session_a_id = extract_running_session_id(text_item(&first_items, 0));
+    let session_a_id = extract_running_cell_id(text_item(&first_items, 0));
     assert_eq!(text_item(&first_items, 1), "session a start");
 
     responses::mount_sse_once(
@@ -1072,7 +1071,7 @@ output_text("session b done");
     let second_request = second_completion.single_request();
     let second_items = custom_tool_output_items(&second_request, "call-2");
     assert_eq!(second_items.len(), 2);
-    let session_b_id = extract_running_session_id(text_item(&second_items, 0));
+    let session_b_id = extract_running_cell_id(text_item(&second_items, 0));
     assert_eq!(text_item(&second_items, 1), "session b start");
 
     fs::write(&session_a_gate, "ready")?;
@@ -1084,7 +1083,7 @@ output_text("session b done");
                 "call-3",
                 "exec_wait",
                 &serde_json::to_string(&serde_json::json!({
-                    "session_id": session_b_id,
+                    "cell_id": session_b_id.clone(),
                     "yield_time_ms": 1_000,
                 }))?,
             ),
@@ -1109,12 +1108,12 @@ output_text("session b done");
     assert_regex_match(
         concat!(
             r"(?s)\A",
-            r"Script running with session ID \d+\nWall time \d+\.\d seconds\nOutput:\n\z"
+            r"Script running with cell ID \d+\nWall time \d+\.\d seconds\nOutput:\n\z"
         ),
         text_item(&third_items, 0),
     );
     assert_eq!(
-        extract_running_session_id(text_item(&third_items, 0)),
+        extract_running_cell_id(text_item(&third_items, 0)),
         session_b_id
     );
 
@@ -1134,7 +1133,7 @@ output_text("session b done");
                 "call-4",
                 "exec_wait",
                 &serde_json::to_string(&serde_json::json!({
-                    "session_id": session_a_id,
+                    "cell_id": session_a_id.clone(),
                     "terminate": true,
                 }))?,
             ),
@@ -1234,7 +1233,7 @@ output_text("after yield");
     assert_regex_match(
         concat!(
             r"(?s)\A",
-            r"Script running with session ID \d+\nWall time \d+\.\d seconds\nOutput:\n\z"
+            r"Script running with cell ID \d+\nWall time \d+\.\d seconds\nOutput:\n\z"
         ),
         text_item(&first_items, 0),
     );
@@ -1327,7 +1326,7 @@ output_text("token one token two token three token four token five token six tok
     let first_items = custom_tool_output_items(&first_request, "call-1");
     assert_eq!(first_items.len(), 2);
     assert_eq!(text_item(&first_items, 1), "phase 1");
-    let session_id = extract_running_session_id(text_item(&first_items, 0));
+    let cell_id = extract_running_cell_id(text_item(&first_items, 0));
 
     fs::write(&completion_gate, "ready")?;
     responses::mount_sse_once(
@@ -1338,7 +1337,7 @@ output_text("token one token two token three token four token five token six tok
                 "call-2",
                 "exec_wait",
                 &serde_json::to_string(&serde_json::json!({
-                    "session_id": session_id,
+                    "cell_id": cell_id.clone(),
                     "yield_time_ms": 1_000,
                     "max_tokens": 6,
                 }))?,