Stabilize exec-server filesystem tests in CI

Move the arg0-based test-binary dispatch bootstrap into a shared test-only crate so core and exec-server can reuse the same current_exe-based harness without keeping exec-server-specific helper logic in codex-arg0.

Co-authored-by: Codex <noreply@openai.com>

codex-rs/exec-server/tests/common/exec_server.rs

@@ -1,5 +1,6 @@
 #![allow(dead_code)]
 
+use std::path::PathBuf;
 use std::process::Stdio;
 use std::time::Duration;
 
@@ -8,7 +9,6 @@ use codex_app_server_protocol::JSONRPCMessage;
 use codex_app_server_protocol::JSONRPCNotification;
 use codex_app_server_protocol::JSONRPCRequest;
 use codex_app_server_protocol::RequestId;
-use codex_utils_cargo_bin::cargo_bin;
 use futures::SinkExt;
 use futures::StreamExt;
 use tempfile::TempDir;
@@ -28,6 +28,7 @@ const EVENT_TIMEOUT: Duration = Duration::from_secs(5);
 
 pub(crate) struct ExecServerHarness {
     _codex_home: TempDir,
+    _helper_paths: TestCodexHelperPaths,
     child: Child,
     websocket_url: String,
     websocket: tokio_tungstenite::WebSocketStream<
@@ -42,10 +43,23 @@ impl Drop for ExecServerHarness {
     }
 }
 
+pub(crate) struct TestCodexHelperPaths {
+    pub(crate) codex_exe: PathBuf,
+    pub(crate) codex_linux_sandbox_exe: Option<PathBuf>,
+}
+
+pub(crate) fn test_codex_helper_paths() -> anyhow::Result<TestCodexHelperPaths> {
+    let (helper_binary, codex_linux_sandbox_exe) = super::current_test_binary_helper_paths()?;
+    Ok(TestCodexHelperPaths {
+        codex_exe: helper_binary,
+        codex_linux_sandbox_exe,
+    })
+}
+
 pub(crate) async fn exec_server() -> anyhow::Result<ExecServerHarness> {
-    let binary = cargo_bin("codex")?;
+    let helper_paths = test_codex_helper_paths()?;
     let codex_home = TempDir::new()?;
-    let mut child = Command::new(binary);
+    let mut child = Command::new(&helper_paths.codex_exe);
     child.args(["exec-server", "--listen", "ws://127.0.0.1:0"]);
     child.stdin(Stdio::null());
     child.stdout(Stdio::piped());
@@ -58,6 +72,7 @@ pub(crate) async fn exec_server() -> anyhow::Result<ExecServerHarness> {
     let (websocket, _) = connect_websocket_when_ready(&websocket_url).await?;
     Ok(ExecServerHarness {
         _codex_home: codex_home,
+        _helper_paths: helper_paths,
         child,
         websocket_url,
         websocket,