Compact Shared Reduced Binary Decision Diagrams with negated identifiers
Found the answer in the paper Shared Binary Decision Diagram with Attributed Edges for Efficient Boolean function Manipulation.

more accurate treatment can be found in section 2.3 in Proving circuit correctness using formal comparison between expected and extracted behaviour (pdf download available).

in short, canonicity is preserved if, quoting from tvandijk.nl/pdf/mscthesis.pdf page 15 "Complement edges" (The Parallelization of Binary Decision Diagram operations for model checking, thesis by Tom van Dijk):

"Minato [35] proposes the following constraints:

1) Only 0 is used as the value of a leaf.

Alternative rule 1 : only 1 is used as the value of a leaf.

Alternative rule 2 : do not allow complement edges on leaves.

2) No complement edges are allowed on 0-edges.

Alternative rule: no complement edges are allowed on 1-edges"

note that this is not a "true" restriction as if we decide that only hi edges are complemented, and we want to create a node with its lo edge being complemented, we just negate the whole node, like a?b:not(c) == not(a?not(b):c).