Verdi Trace X (tfgTrX) runs headless in -nogui batch

Synopsys Verdi's automatic X root-cause trace works without the GUI: in a -nogui -play Tcl script run tfgSetupTFV, then tfgBehaviorAnalysis, then tfgTrX -win [tfgGetWindow] -folder "sig#time" -time time sig -batchOutput out.rst -showTracePath -causeCnt 1 -noBBox. The .rst lists the root cause (e.g. 'X from un-initialized storage element') and the trace path. Caveats: on a CPU core it can run unbounded (we saw >10 min and ~10 GB RSS), so add a memory and time guard; struct-typed regs can come back as 'Black box output'. For manual walks, srcActiveTrace does not move the cursor in -nogui; get a signal's last transition with wvAddSignal + wvSelectSignal + wvSetCursor + wvGetSearchPrevTime.