built, the KEA_CONTROL_SOCKET_DIR appears to be honored fine

router # [    8.927187] kea-ctrl-agent[805]: 2025-07-08 22:43:26.795 INFO  [kea-ctrl-agent.dctl/805.140519184328576] DCTL_STARTING Control-agent starting, pid: 805, version: 2.6.3 (stable)
router # [    8.929422] kea-ctrl-agent[805]: 2025-07-08 22:43:26.798 ERROR [kea-ctrl-agent.ctrl-agent/805.140519184328576] CTRL_AGENT_CONFIG_FAIL Control Agent configuration failed: invalid path specified: '/run/kea/VALUE-IN-CONFIG', supported path is '/run/kea/meow'
router # [    8.931635] kea-ctrl-agent[805]: 2025-07-08 22:43:26.798 FATAL [kea-ctrl-agent.dctl/805.140519184328576] DCTL_CONFIG_FILE_LOAD_FAIL Control-agent reason: invalid path specified: '/run/kea/VALUE-IN-CONFIG', supported path is '/run/kea/meow'

then there's a permission issue, checking

router # [    8.841737] kea-ctrl-agent[780]: 2025-07-08 22:45:53.570 ERROR [kea-ctrl-agent.ctrl-agent/780.139821817276288] CTRL_AGENT_CONFIG_FAIL Control Agent configuration failed: socket path:/run/kea does not exist or does not have permssions = 750

    RuntimeDirectoryMode = "750";