Function merged_into_trunk 

pub fn merged_into_trunk(
    primary: &Path,
    trunk: &str,
) -> Result<BTreeSet<String>>

Every local branch reachable from trunk or from the remote-tracking branch trunk follows. A local trunk that has fallen behind its remote — a primary checkout nobody has pulled, because a session holds uncommitted work in it — would otherwise call every branch that landed since unmerged, and cleanup would offer nothing; a branch the remote trunk contains is published and integrated, which is the safety cleanup asks for.

use majordomus_cli::worktree::state::merged_into_trunk;
use std::process::Command;
let dir = tempfile::tempdir().unwrap();
let git = |args: &[&str]| {
    let ok = Command::new("git")
        .arg("-C")
        .arg(dir.path())
        .args(args)
        .env("GIT_AUTHOR_NAME", "t")
        .env("GIT_AUTHOR_EMAIL", "t@example.com")
        .env("GIT_COMMITTER_NAME", "t")
        .env("GIT_COMMITTER_EMAIL", "t@example.com")
        .status()
        .unwrap()
        .success();
    assert!(ok, "git {args:?}");
};
git(&["init", "-q", "-b", "main"]);
git(&["commit", "-q", "--allow-empty", "-m", "base"]);
git(&["branch", "landed"]);
// no upstream here: the local trunk alone decides, and it contains `landed`
let merged = merged_into_trunk(dir.path(), "main").unwrap();
assert!(merged.contains("landed"));