Solve continuous integration (pending head / commit queue) problem using git

Hi !

  This is my first mail on the list so hello everyone :)
  I'am currently write my MA. Part of my thesis is looking for some
way to stay "master" stable.
  First assumption is simple: Control version system make all dirty
job - programmers can't "stop" or "break" all procedure and work in
natural ways. We can't assume that programmer use some custom hooks on
their side or add some addition parameters to git commands.
  Second assumption  is that programmer can't compile source code one
their machine for some reasons. Only way to compile is some other way
- for example use CruiseControl or Hudson or some CI tools. This isn't
really matter in my question now.
  Third assumption: Code cloned from repository is stable = compiling
well and pass all tests.
  Forth assumption: compiling is testing are very very very fast.

What I meen "natural way of work" by programmer. They *clone* repository (or *pull* changes) from some central repository. Then do some stuff with code on their working copy and *push* their changes. Ok but - their don't know is code working well. And this is a problem. I know there is some options: XP pair programming, automated static code analysis, code review and others ... but this is not the point. In my "configuration" there are some frequently scheduled build of system automated by some tool. Tool just get all stuff from repo, compile all stuff, running tests (if compiling successes) and if sending e-mail. But SCM should "somehow" distinct unstable commits from stable commits (after compiling).

Now. My idea. There is some revision tagged as "stable". *Clone* and *pull* operations is somehow "overloaded" from server side and always! return last revision tagged as stable. After compiling external tool just move tag to another revision which pass all tests. Of course there is some additional parameter (for example --last or --unstable) which can clone fine way of repository.

Two questions.
1) Maybe I try to invent the wheel again. Is there any way to take the
effect without overloading standard git behaviours.
2) If not how overload git behaviors on git "server side" repo?

Thanks in advance!