Mailbox - inter-thread communication mechanizm was migrated from zig 0.14.1 to zig 0.15.2.
As result of migration it got TypeErased Mailbox
an intrusive_ mailbox that does not know the message type
This implementation relies on De-Genericify Linked Lists introduced in Zig 0.15.1.
Since all of my projects depend on Mailbox, starting this migration has really opened a Pandora’s box 
I’m hoping there are other ‘migrants’ already shared helpful stories here…