in absence of any documentation to the contrary in https://perldoc.perl.org/perlop.html#Comma-Operator I would expect the operator to force scalar context.

It's documented in List value constructors:

LISTs do automatic interpolation of sublists. That is, when a LIST is evaluated, each element of the list is evaluated in list context, and the resulting list value is interpolated into LIST just as if each individual element were a member of LIST.

A cross-reference between the two docs probably wouldn't hurt.

You might be interested in PerlX::Maybe.

I have to admit that I'm not even sure what the documentation for m// means when it says the search returns true or false, since Perl doesn't have explicit boolean values.

See Truth and Falsehood (there used to be a section in the Perl docs).