?null / ?back unimplemented
Home §"URI structure" and URI list ?null (no-branch) and ?back (previous-branch) as live ref shapes, but no code path interprets them — they resolve as ordinary branch names and fail as a missing ref. The goal is to honour the two documented magic refs (or, if abandoned, strike them from the spec). See URI, Home.
?null/?back are treated as literal branch names everywhere; there is no magic-ref interception.
keeper/RESOLVE.c resolve_branch_path (~:63) does a literal REFS lookup for null/back → RESLVNONE; KEEPResolveRef (~:228) has no special case.dog/DOG.c DOGNormalizeArg/DOGCanonURI do not rewrite null/back; a grep across beagle/dog/keeper/graf/sniff finds zero magic-ref code (only tokenizer keyword tables).be get ?back therefore fails as "missing ref" instead of switching to the previous branch; ?null cannot detach to no-branch.Needs a user ruling: implement the two magic refs, or remove them from Home/URI as never-built.
Decide, then either add the intercept or strike the spec lines.
null/back in DOGCanonURI (or KEEPResolveRef); back reads the prior get/post row's ?branch from the wtlog, null maps to the detached/no-branch state.be get ?back after a switch returns to the prior branch; ?null detaches.