Nix wrote half of my debugger

The author describes how Nix's package management system provided much of the infrastructure needed to build Rewind VM, a deterministic virtual machine that helps identify race conditions in builds by replaying executions with perturbed thread schedules. Rather than building debugging features from scratch, the author repeatedly found that Nix had already solved the hard parts—such as gathering exact program inputs, debug symbols, and source code—through its derivation system. The tool successfully demonstrates its utility by pinpointing the exact step where race conditions occur, as shown in a bank account example where it identified a critical scheduling decision among thousands of steps.