`REA_JAVASCRIPT_PRLIMIT_COMMAND` and `REA_MITMDUMP_COMMAND` were admitted
after an access check alone, which a searchable directory passes. Admission
then succeeded, and the failure surfaced later as a launch-time adapter
error instead of the capability refusal that names the configured path.
Require a regular file, as #751 did for the firmware engine and limiter.
Linux-only tests mirror that change; both checks only run on Linux hosts.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>