Function get_mux_data_dir 

pub fn get_mux_data_dir() -> PathBuf

Get the AgentMux root directory (~/.agentmux).

Delegates to agentmux_common::data_paths::agentmux_root, which is the single resolver for this path. This function used to compute it itself, reading AGENTMUX_DATA_HOME where the common crate read AGENTMUX_HOME_OVERRIDE — two resolvers, two env vars, and two different answers if either was set. Both are now honoured by the one resolver, so an existing install finds its data exactly where it did before. A10 of docs/analysis/TRACKING_ARCHITECTURE_REFACTOR_A1_A15_2026_06_18.md.

The old local copy fell back to PathBuf::from("/") when home_dir() returned None, which meant a host with no resolvable home silently wrote to /.agentmux. That fallback is deliberately NOT preserved: the resolver returns Err, and rather than inventing a path this keeps the pre-existing shape of the API by falling back to the same ~/.agentmux expression only when a home DOES exist. If it does not, writing to the filesystem root is never the right answer.