At the very end of the script you can see where the callback is called.

The issue is fixed because with the quoted lambda when org tries to
write it into the async build script (I.E. `(message "%s" callback-function)`)
it'll be outputted verbatim (as a lisp expression).
Instead my emacs atm represents the lambda as some anonymous function object
(resembling `#<subr F616e6f6e796d6f75732d6c616d626461_anonymous_lambda_77>`)
so when org tries to print it out it'll just print this garbage
representation instead of the function it should call.

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Mohsin K.