synchronizing 2 heterogenous branches by cherry-pick

[Martin Pirker <git.collector@gmail.com>]

One of those weird real-world situations, advice appreciated:

Given...
one Git repository with
one branch "left" and one branch "right"
both branches have a different history (common ancestor is 0000000)
both branches have different content
_however_, at one specific commit in the "left" and "right"
branch it can be said that the content of specific
subdirectories is identical
these commits are marked with a tag "equal"

Thus, patches which only modify the identical
content can always be applied without conflicts on both branches.
I commit a new patch on "left", I can cherry-pick it to
"right" and both trees are identical again.

Issues:
Cheery-pick takes only one commit.
I have to find commits by hand.
Ideally, I want to specify equal..HEAD, if 10 commits are "left"
and "right" are 7, well, then cherry pick the last 3 from "left"
to "right".
Note that the patch content is always identical, the
commit text message (author/committer/timestamp/...) not
always
Note that ideally only one way synchronizing occurs. Bonus
points if I can add on both sides and then start magic sync...


Any good idea on how to automagically script these cherry-picking?

Martin