The recipe bootstrapping tool reads a build.proto from stdin, resolves the appropriate recipe version to use, and executes the build.
The tool implements the luciexe protocol. Fuchsia Buildbucket builders which require recipe versioning should configure the tool as their executable. See the lucicfg documentation for more information.
The “recipe version” is a recipes.git revision, which is resolved through a decision tree on build.proto. See main file.
Once the recipe version is resolved, a checkout of recipes.git is performed. Within the checkout, recipes.py luciexe is exec'd to advance into build execution.