Hacker News Reader

Is it similar to Zig’s callconv keyword?

Guess so. Unfamiliar with Zig. The point is that not a "all or nothing" strategy for a compilation unit.

Debugger writers may not be happy, but maybe lldb supports all conventions supported by llvm.

Debugger writers have dealt with different calling conventions for decades. The notion predates C even. They can handle it just fine.