Salvage the unit-budget implementation from #104745, replacing its test matrix with two invariant tests and covering the sibling graceful start. Keep unprivileged property reads, finite fallbacks, real manager errors, and post-restart health verification. Native disposable user unit: old client timed out after 15.03 seconds; new client completed the same 16-second stop transaction in 16.13 seconds. The unit stayed active with a new PID; missing-unit errors stayed errors. Co-authored-by: Teknium <127238744+teknium1@users.noreply.github.com>