Maybe useful inspiration from TCL: there are many commands that define new variables, which makes modeling the stack unnecessary.

For example:

  lappend responses [dict status 200 body ...]

I can see that being an attribute:

  <request-send url="..." as="greeting" />
  <response-text response="greeting" as="text" />
  <selection-set-text text="text" />

The main reason for using a stack was reducing verbosity because for short scripts using variables felt unnecessary when the type-prefix of the command already communicates the variable contents. But it could still be a good idea to have a shorter syntax for assigned variables.

Accessing a variables works like this at the moment:

  <selection-set-text $text="varname">

  <response-get-text $="varname">