I personally approaches stashes as undoable "clean up", and I never have anything really important that I want to save there. If I do have something like that, I just commit with a "WIP <some-descriptive-string>" message and don't push it, then a "git reset --mixed HEAD^" when I want to get back to it.
However, just FYI: you can "grep" your stashes really easily if you want to. just "git stash list -p" gives you the diffs for all the stashes, by default in "less" where you can search them, but you can pipe it to grep if you want. I somewhat frequently do that with "git log", if I want to know "when did this variable change?" or whatever, just "git log -p" to get the log with diffs in less, then search for whatever it was with a slash.
Neat.
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https://github.com/neilbrown/wiggle
although on debian based systems I think you can just "apt install wiggle"
I know about wiggle, but I have not used it, to be honest.
git-send-email also has some quirks for Outlook which have been recently merged.
Exchange historically had a tendency to mangle emails sent through it (whitespace changes, line wrap, etc), which is obviously bad news for patchmails. I dunno if it's any better these days.
[1]: https://drewdevault.com/2022/07/25/Code-review-with-aerc.htm...
And I think you may underestimate the power of stgit. You can manage thousands of patches concurrently, no problem. If you're a maintainer getting patches from loads of people all the time, this is valuable. stgit has it's origins in quilt, which in turn has its origins in Andrew Morton's patch scripts[1], and I know for a fact that Andrew Morton actually managed thousands of patches at a time for years in his work on the linux kernel, because I once sent him a patch against those scripts, and he complained it was slow because I used an O(n^2) algorithm, which worked fine with a handful of patches, and I asked him how many patches he had, and he told me a number that was multiple thousands, so this isn't a hypothetical example.
Then you don't need that message to be in a file-based inbox that is accessible from your git repo.
And in that case you are still likely going to have to copy and paste something to get the correct path.