How to `git blame` individual characters?

[Jan Keromnes]

Dear Git developers,

I'd like to understand what would be required to run `git blame` on
individual characters instead of full lines. Could you please point me
in the right direction?

Someone asked a similar question about "Word-by-word blame/annotate"
on StackOverflow a few years ago, and one of the replies said:

> Git tracks changes snapshot by snapshot. The line-based format is calculated 
> on-the-fly, and it would also be possible to have a word-based format.

Source: https://stackoverflow.com/q/17758008/3461173

This leaves me hopeful that a character-based format can somehow be
achieved. Here is a fake example to illustrate what I'm looking for:

        $ cat myscript.js
        for (int foo = 0; foo <= 11; foo++) { console.log(foo); }
        $ git blame --character-based --pseudo-json myscript.js
        [
            { "commit": "abcd1234", "summary": "Implement loop",
"characters": "for (int " },
            { "commit": "bcd1234a", "summary": "Rename iterator",
"characters": "foo" },
            { "commit": "abcd1234", "summary": "Implement loop",
"characters": " = 0; " },
            { "commit": "bcd1234a", "summary": "Rename iterator",
"characters": "foo" },
            { "commit": "abcd1234", "summary": "Implement loop",
"characters": " <= " },
            { "commit": "cd1234ab", "summary": "Go up to 11",
"characters": "11" },
            { "commit": "abcd1234", "summary": "Implement loop",
"characters": "; " },
            { "commit": "bcd1234a", "summary": "Rename iterator",
"characters": "foo" },
            { "commit": "abcd1234", "summary": "Implement loop",
"characters": "++) { console.log(" },
            { "commit": "bcd1234a", "summary": "Rename iterator",
"characters": "foo" },
            { "commit": "abcd1234", "summary": "Implement loop",
"characters": ")" },
            { "commit": "d1234abc", "summary": "Add missing
semicolon", "characters": ";" },
            { "commit": "abcd1234", "summary": "Implement loop",
"characters": " }" }
        ]

What would be the most direct way to achieve such a character-based
blame/annotate? Should I write some sort of Git extension, or hack
into Git's source code?

E.g. I looked for an option in `git-blame` or `git-annotate` to change
the "next line boundary" from "carret return" (line-based blame) to
"any whitespace" (word-based blame) or "character-by-character"
(character-based blame), but I didn't find it. Could this be
implemented in `blame.c`? If so, which methods would need tweaking?

Many thanks!
Jan