Secagentd is a daemon responsible for detecting and reporting security related events through ERP (Encrypted Reporting Pipeline) for forensic analysis.
Since this feature is under active development it will not be enabled by default when building an image.
To build all the packages for a board with this feature enabled you must
USE="bpf_extras secagent" build_packages --board="${BOARD}"
If you wish to upgrade an existing board image to include this feature you should emerge the kernel
e.g:
USE="bpf_extras" emerge-amd64-generic chromeos-kernel-5_15
then you can successfully build and install secagentd
emerge-amd64-generic secagentd