The settlement-time CPU recheck compared spent CPU against the configured
cpuSeconds, but _clamped may have lowered the effective soft limit to a stricter
inherited value. A program that traps SIGXCPU, burns past the inherited soft,
and returns inside the soft-to-hard gap was checked against the configured value
and falsely reported successful, bypassing the inherited limit. The recheck now
uses the clamped cpu_soft. Adds a regression test that inherits a 1s soft CPU
limit and asserts a SIGXCPU-trapping over-burn is a timeout, not a success.
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