T34: review round 3: PowerShell keeps a program's code unless the line surely ends in PowerShell, a cmdlet, a name not found or no command, so a call through a variable keeps it; bash without promptvars, zsh without prompt_percent and PowerShell without PSReadLine say at start what they cannot mark

assets/shell-integration/bash/elyterminal.bash

@@ -52,3 +52,5 @@ _ely_mark() {
   fi
 }
 PROMPT_COMMAND="_ely_prompt${PROMPT_COMMAND:+;$PROMPT_COMMAND};_ely_mark"
+# PS0 and the prompt mark a command only through expansions, which promptvars turns on.
+builtin shopt -q promptvars || builtin printf 'ELYTerminal: bash marks no command while promptvars is off (shopt -s promptvars)\n' >&2