Verdi batch active trace: -nogui -play Tcl loop and its gotchas

A warm verdi -nogui -dbdir simv.daidir -ssf dump.fsdb -play serve.tcl session with a stdin loop (gets stdin / uplevel #0) answers srcSetCursorTime t; srcActiveTrace sig in about 0.1-2 s after a ~16 s start. Gotchas: Verdi prints warnings like 'Unrecognized signal' without a trailing newline, so print each reply after a leading newline and filter lines by prefix; relative file paths are relative to the vcs compile dir; srcTraceDriver returns only one driver; active trace follows port connections to the real driver; a missing seat prints '[ERROR] Could not checkout ... license' and exits 1 (the 'Elite not available, try Apex' warning appears even on success). Cursor time is in the window time unit (wvGetWindowTimeUnit), so check it equals wvGetFileTimeUnit.