VCS RTL edit loop measured in seconds

VCS W-2024.09 debug_access+all/KDB on EWS: tiny fixture changed compile 2.14-2.18s plus run 0.39-0.42s. Teaching CPU/testbench clean build 5.59s; one-line ALU edit recompiles only ex_stg yet rebuild costs 4.63-4.70s across three edits. Full short test 0.90-0.92s, total ~5.60s. Wrong arithmetic triggers checker early in ~0.52s, total ~5.20s, which is early-failure feedback rather than full replay. Checker fatal still returned zero: inspect logs. Scratch copies, not original project. No claim about hot patching or long-regression costs.