It seems to work correctly if you include the last two lines in the first commit.

    jj-workshop on  HEAD (2cab0f1) [!]
    > jj
    @  unwquwxk samfredrickson@gmail.com 2025-07-29 18:47:18 f7db7c8a
    │  Part 2 first
    ○  wskswvnt samfredrickson@gmail.com 2025-07-29 18:47:13 git_head() 2cab0f16
    │  Part 2 second
    ◆  pnxpmvpz jkoppel@users.noreply.github.com 2025-07-27 21:54:50 main 4d04bcef
    │  Update README.md with link to JJ homepage
    ~
    
    jj-workshop on  HEAD (2cab0f1) [!]
    > jj show w --git
    Commit ID: 2cab0f167c64cea1d23407e12196fa6d1b8aab25
    Change ID: wskswvntlvtwzqutoowyqltsouklzmqr
    Author   : Sam Fredrickson <samfredrickson@gmail.com> (2025-07-29 18:34:52)
    Committer: Sam Fredrickson <samfredrickson@gmail.com> (2025-07-29 18:47:13)
    
        Part 2 second
    
    diff --git a/part1/foo.txt b/part1/foo.txt
    index 067f76475a..56c99c9cc3 100644
    --- a/part1/foo.txt
    +++ b/part1/foo.txt
    @@ -6,5 +6,5 @@
    
     * The best operating system is ______
     * The best text editor is ______
    -* The best kind of phone is _______
    -* The best superhero is ___________
    +* The best kind of phone is nothing
    +* The best superhero is nobody
    
    jj-workshop on  HEAD (2cab0f1) [!]
    > jj show u --git
    Commit ID: f7db7c8a5f37df8c29e08a6697ca6cd59c2313c4
    Change ID: unwquwxklkprlqoksmxzvoumspnmnknk
    Author   : Sam Fredrickson <samfredrickson@gmail.com> (2025-07-29 18:34:52)
    Committer: Sam Fredrickson <samfredrickson@gmail.com> (2025-07-29 18:47:18)
    
        Part 2 first
    
    diff --git a/part1/foo.txt b/part1/foo.txt
    index 56c99c9cc3..f48ae9b3f9 100644
    --- a/part1/foo.txt
    +++ b/part1/foo.txt
    @@ -4,7 +4,7 @@
    
     Maybe fill this out?
    
    -* The best operating system is ______
    -* The best text editor is ______
    +* The best operating system is Linux
    +* The best text editor is neovim
     * The best kind of phone is nothing
     * The best superhero is nobody