core: make shell behavior portable on FreeBSD (#7039)

- Use /bin/sh instead of /bin/bash on FreeBSD/OpenBSD in the process
group timeout test to avoid command-not-found failures.

- Accept /usr/local/bin/bash as a valid SHELL path to match common
FreeBSD installations.

- Switch the shell serialization duration test to /bin/sh for improved
portability across Unix platforms.

With this change, `cargo test -p codex-core --lib` runs and passes on
FreeBSD.

codex-rs/core/src/exec.rs

@@ -781,6 +781,15 @@ mod tests {
     #[cfg(unix)]
     #[tokio::test]
     async fn kill_child_process_group_kills_grandchildren_on_timeout() -> Result<()> {
+        // On Linux/macOS, /bin/bash is typically present; on FreeBSD/OpenBSD,
+        // prefer /bin/sh to avoid NotFound errors.
+        #[cfg(any(target_os = "freebsd", target_os = "openbsd"))]
+        let command = vec![
+            "/bin/sh".to_string(),
+            "-c".to_string(),
+            "sleep 60 & echo $!; sleep 60".to_string(),
+        ];
+        #[cfg(all(unix, not(any(target_os = "freebsd", target_os = "openbsd"))))]
         let command = vec![
             "/bin/bash".to_string(),
             "-c".to_string(),

codex-rs/core/src/shell.rs

@@ -358,7 +358,8 @@ mod tests {
 
         assert!(
             shell_path == PathBuf::from("/bin/bash")
-                || shell_path == PathBuf::from("/usr/bin/bash"),
+                || shell_path == PathBuf::from("/usr/bin/bash")
+                || shell_path == PathBuf::from("/usr/local/bin/bash"),
             "shell path: {shell_path:?}",
         );
     }

codex-rs/core/tests/suite/shell_serialization.rs

@@ -366,7 +366,7 @@ async fn shell_output_for_freeform_tool_records_duration(
     let test = builder.build(&server).await?;
 
     let call_id = "shell-structured";
-    let responses = shell_responses(call_id, vec!["/bin/bash", "-c", "sleep 1"], output_type)?;
+    let responses = shell_responses(call_id, vec!["/bin/sh", "-c", "sleep 1"], output_type)?;
     let mock = mount_sse_sequence(&server, responses).await;
 
     test.submit_turn_with_policy(