How to continue a git merge where someone pushed by marking all files as "resolved"?

My friend

run git merge master
resolved some of the conflicts
marked all of the files as "resolved"
pushed the merge commit to a temp branch

I pulled the branch. I can see diff lines in the files like

<<<<<<< HEAD
text1
=======
text2
>>>>>>> origin/master

How can I simulate the merge where my friend left off?

I am ok with the solutions which include some pull/checkouts into other places, some copy/paste commands, other commands/tools to detect diff parts etc.

Solution

I would not try to recover from your friend's work, but rather redo the merge from scratch.

Find your friend's merged commit and use git log --graph or git log --format=fuller to determine its parent commits:

E.g., I have 39184c481a which is a merge of 2aa69455a3 into 1d3c2f45f6.

git log --format=fuller 39184c481a

commit 39184c481a
Merge: 1d3c2f45f6 2aa69455a3
Author: ...

Then checkout the original first parent and merge the other parent into it

git checkout 1d3c2f45f6
git merge 2aa69455a3

and now I'm in the same state I was when the commit was done. So from here you should be able to redo the conflict resolution.

You probably want to give yourself a branch to be able to find this work later:

git checkout -b dev.fixing-the-merge

And eventually merge this back into your main branch, or possibly rewrite the history with a git push --force if your team is willing to let you do that.