diff --git a/codex-rs/rmcp-client/tests/mcp_2026_stdio.rs b/codex-rs/rmcp-client/tests/mcp_2026_stdio.rs
index 53ba7fbb95..3c7e5ee117 100644
--- a/codex-rs/rmcp-client/tests/mcp_2026_stdio.rs
+++ b/codex-rs/rmcp-client/tests/mcp_2026_stdio.rs
@@ -55,10 +55,26 @@ async fn exercise_stdio_server(
     } else {
         use std::os::unix::fs::PermissionsExt;
         let wrapper = root.path().join("server");
-        std::fs::write(
-            &wrapper,
-            "#!/bin/sh\nprintf '%s' \"$0\" > argv0\nexec \"$MCP_SERVER\" \"$@\"\n",
-        )?;
+        let script = "#!/bin/sh\nprintf '%s' \"$0\" > argv0\nexec \"$MCP_SERVER\" \"$@\"\n";
+        #[cfg(target_os = "linux")]
+        {
+            // Keep the writable descriptor out of this process so concurrent test
+            // spawns cannot inherit it and cause ETXTBSY when launching the wrapper.
+            let output = std::process::Command::new("/bin/sh")
+                .arg("-c")
+                .arg("printf '%s' \"$1\" > \"$2\"")
+                .arg("write-mcp-fixture")
+                .arg(script)
+                .arg(&wrapper)
+                .output()?;
+            anyhow::ensure!(
+                output.status.success(),
+                "failed to write MCP wrapper: {}",
+                String::from_utf8_lossy(&output.stderr)
+            );
+        }
+        #[cfg(not(target_os = "linux"))]
+        std::fs::write(&wrapper, script)?;
         std::fs::set_permissions(wrapper, std::fs::Permissions::from_mode(0o755))?;
         env.insert(OsString::from("MCP_SERVER"), server.into_os_string());
         (