>The stuff in your sandbox should build on *any* Unix system.  Tool X 
>shouldn't contain any dependencies on itself or any tools that require X 
>to already exist before they can be built: mathematically, the 
>dependencies should be a directed acyclic graph.

I think you misunderstand.  Historically, sometimes the dependencies
_are_ cyclic unless you use source-code version info to disambiguate
the graph and make it acyclic.

You seem to bea assuming that there are no such version-based
dependencies between the tools in the "sandbox".  Historically, there
_have been_; that's a fact.
it.

When it happens, You need to apply versioning info in order to know
which order to re-build the sandbox tools in, and you may need to
start using the sandbox tools to build the rest of the sandbox, rather
than the old system tools.  That is the part that is Not Tractable to
Automation.  That's part of why we have snapshots; developers solve
the problem manually.

I agree that a sandbox (and the build-as-not-root) would help, but
would they help enough to be worth it?  If so, you need to find
someone who has spare cycles to implement it -- perhaps as part of
the cross-compile tools.