FR: Support for opening a hunk in an editor from the built-in merge tool #8212
Description
Is your feature request related to a problem? Please describe.
Sometimes the correct resolution for a merge isn't to take the base/theirs/yours version of a line, but to take some combination of them. The built-in jj merge tool doesn't seem to support that.
Describe the solution you'd like
Something like what git checkout -p supports: an option to open the conflicting hunk in a text editor, so I can edit it to contain the proper merge result and continue with the merge operation.
Describe alternatives you've considered
#5453 covers a related request: to be able to leave some parts of the merge unresolved. This would address the use case, but is less convenient and requires more context-switching, multiple passes, and manually tracking down the remaining unmerged hunks.