[QUESTION] about .git/info/grafts file

Hi,

I'm wondering why the "grafts" files is not involved during push/pull/clone operations ?

Another question regarding grafting use case. Let's say I have my origin branch looks like:

               origin ---0---1---<snip>---300 000---300 001---300 002

Let's say that the 300 000th commit is where I started my work by using:

               $ git-checkout -b master <300 000 shaid>

I do some work on master branch and get the following

                                                 a---b---c---d master
                                                /
               origin ---0---1---...---300,000---300,001---300,002

Now, I would like to make my own public repository based on my work but before pushing master branch in that repo I would like to get rid of all unused commits [0 299,999]. Indeed each of these commits do not have useful history for my work. So I used grafts things to have:

                              a---b---c---d master
                             /
               origin 300,000---300,001---300,002

But now if I ask to git for:

               $ git-merge-base master origin
               # nothing

So git failed to found the common commit object which should be 300,000. Why ?

In other the hand, if I use grafting to get:

                                               a---b---c---d master
                                              /
               origin 2999,999---300,000---300,001---300,002

              $ git-merge-base master origin
              2dcaaf2decd31ac9a21d616604c0a7c1fa65d5a4

So now git found the common commit. Can anybody explain me why ?

Do you think it's a good usage of git ? Or should I do otherwise to setup my public repository ?

Thanks
--
               Franck