How to programmatically git checkout a file partially

Here is what I'm doing. add a pre-commit hook using npm scripts, an example repo

"is-commitable": "git status | grep 'Changes to be committed:'",
"stash-pop": "git stash pop >> /dev/null",
"stash-unstaged": "git stash save -k --include-untracked 'unstaged-stash' >> /dev/null",
"check-commitable": "npm run is-commitable || (npm run stash-pop && exit 1)",
"lint-staged": "(eslint . --fix && git add .) || (npm run stash-pop && exit 1)",
"recheck-commitable": "npm run check-commitable",
"stash-linted": "git stash save 'linted-stash' >> /dev/null",
"stash-pop-unstaged": "git stash pop stash@{1}",
"stash-pop-linted": "git read-tree stash && git stash drop",
"clean-lint-staged": "(lint-staged >> /dev/null) || exit 0"

Example

1. have two lines of commited code:

   line1
   line2
   
   

2. make some changes:

   * line1-changed
   * line2-changed
   
   

3. partially add one of them:

   - line1
   + line1-changed
   * line2-changed
   
   

4. run commit and pre-commit hook is triggered

   • stash-unstaged

     - line1
     + line1-changed
     line2(changed part been stashed in unstaged-stash)
     
     

   • lint-staged

     - line1
     + line1-fixed
     line2(changed part been stashed in unstaged-stash)
     
     

   • stash-linted

     line1(changed and fixed part been stashed in linted-stash)
     line2(changed part been stashed in unstaged-stash)
     
     

   • stash-pop-unstaged

     line1(changed and fixed part been stashed in linted-stash)
     * line2-changed
     
     

   • stash-pop-linted

     - line1
     + line1-fixed
     * line1-changed
     * line2-changed
     
     

   • clean-lint-staged

     - line1
     + line1-fixed
     * line2-fixed
     
     

Problem

The last 2 steps are not perfect.

Expected result

I wanted to get

- line1
+ line1-fixed
* line2-changed

Actual results

But now I can only get

- line1
+ line1-fixed
* line1-changed
* line2-changed

or

- line1
+ line1-fixed
* line2-fixed

Need help

So can I find a way to programmatically git checkout a file only the staged lines?

Or drop the last step find a way to fix the last 2nd step

via Stupidism