cmux ssh: "ancestor writable by other users without sticky-directory protection" on Ubuntu EC2

cmux ssh <host> failed with: could not prepare secure daemon state directory ~/.local/state/cmux/remote/sessions/...: secure directory has an ancestor writable by other users without sticky-directory protection, then timed out after ~89s.

Cause: on stock Ubuntu (EC2 ubuntu user) umask is 002, so ~/.local and ~/.local/state are drwxrwxr-x (group-writable). cmux rejects any group/other-writable ancestor.

Fix on the remote: chmod go-w ~/.local ~/.local/state (and any other g+w dirs under ~, e.g. find ~ -maxdepth 4 -type d -perm -g+w -exec chmod go-w {} +). Add umask 022 to ~/.profile so new dirs are not group-writable.