Dependency and build state is kept inside .redo subdirectory in each directory related the build. Each corresponding target has its own, recreated with every rebuild, .rec file. It is recfile, that could have various dependency information. For example:
Build: 80143f04-bfff-4673-950c-081d712f573d Type: ifcreate Target: foo.o.do Type: ifchange Target: default.o.do Size: 123 InodeNum: 2345 CtimeSec: 1605721341 CtimeNsec: 253305000 MtimeSec: 1645606823 MtimeNsec: 369936700 Hash: f4929732f96f11e6d4ebe94536b5edef426d00ed0146853e37a87f4295e18eda Type: always Type: stamp Hash: 5bbdf635932cb16b9127e69b6f3872577efed338f0a4ab6f2c7ca3df6ce50cc9
And the schema definition:
%rec: Build
%doc: Build session
%key: Build
%type: Build uuid
%rec: Dependency
%doc: Dependency information
%mandatory: Type
%allowed: Target Size InodeNum CtimeSec CtimeNsec MtimeSec MtimeNsec Hash
%unique: Type Target Size InodeNum CtimeSec CtimeNsec MtimeSec MtimeNsec Hash
%type: Type enum ifcreate ifchange always stamp
%type: Size int
%type: InodeNum int
%type: CtimeSec int
%type: CtimeNsec int
%type: MtimeSec int
%type: MtimeNsec int
%type: Hash regexp /[0-9a-f]{64}/