>...AFAIK, where reprocessing of plutonium from CANDU reactors was used to bootstrap nuclear warhead production.
No, India appears to ave gotten plutonium from a small research reactor, not a CANDU reactor (though it was provided by Canada):
>...The test used plutonium produced in the Canadian-supplied CIRUS reactor, and raised concerns that nuclear technology supplied for peaceful purposes could be diverted to weapons purposes.
https://en.wikipedia.org/wiki/India_and_weapons_of_mass_dest...
>...CIRUS (Canada India Reactor Utility Services)[1][2][3] was a research reactor at the Bhabha Atomic Research Center (BARC) in Trombay near Mumbai, India. CIRUS was supplied by Canada in 1954, but used heavy water (deuterium oxide) supplied by the United States. It was the second nuclear reactor to be built in India.
It was modeled on the Canadian Chalk River National Research X-perimental (NRX) reactor
https://en.wikipedia.org/wiki/CIRUS_reactor