Root cause: Tk registers a main loop (Tcl_SetMainLoop); tclsh''s Tcl_Main
services it after the script, so `tclsh gui.tcl` behaves like wish. The
script subcommand sourced-then-exited, so a Tk script''s after-callbacks
never ran (scriptlib/tktimer.tcl flashed and died; shell was the
workaround). Confirmed: native tclsh tktimer 1 blocks ~1.35s; script did
0.38s.
Fix: after the script body (success paths only), if a Tk main loop is
registered (info exists ::tk_version && winfo exists .), tkwait window .
services the event loop until the main window closes, then exit - the
script-level equivalent of Tcl_Main. A script that exits from a callback
(tktimer countdown) terminates directly. Console scripts have no main
loop and exit at once; a script error exits at once (no hanging window).
Verified both generations: tktimer via script now blocks the countdown
(punk902z 1.49s, punksys 1.57s - Tk present in both) exit 0; tkhello_exit
immediate; tk-script-that-errors exit 1 in 0.37s (no hang); tkhello (no
self-close) blocks like wish; console script unaffected. Enables G-020
GUI automation via `script` instead of `shell` (noted in G-020 detail).
Project version 0.4.1.
Assisted-by: harness=claude; primary-model=claude-fable-5; api-location=anthropic.com
