[Bug]: gh stack modify doesn't work #629

Describe the bug

gh stack modify consistently fails with this error:

✗ a modify was completed but the stack has not been submitted yet
Run `gh stack submit` to push changes and recreate the stack on GitHub

I first had this issue on a stack where I had manually modified the order of the branches, and wanted to update the stack to keep it in sync using gh stack modify (possibly not supported behavior).

But then I tried it on a brand new stack (completely different branches) which I had just submitted, and it still fails with the same error, even immediately after a successful gh stack submit.

Affected command

gh stack modify

gh-stack version

gh stack version 0.3.0

GitHub CLI version

gh version 2.103.0 (2026-10-21)

Operating system

macOS 26.6

Shell

zsh

Steps to reproduce

• Create a stack
• gh stack submit
• gh stack modify

Expected behavior

gh stack modify lets you modify the stack.

Actual behavior

~/dev/my/repo » gh stack modify
✗ a modify was completed but the stack has not been submitted yet
Run `gh stack submit` to push changes and recreate the stack on GitHub

Terminal output

~/dev/my-repo » gh stack submit
Checking stack state...
Pushing to origin...
PR #111 for my-stack-branch is up to date
✓ Created PR #222 for another-stack-branch
✓ Stack created on GitHub with 2 PRs (stack #333)
✓ Pushed and synced 2 branches

~/dev/my-repo » gh stack modify
✗ a modify was completed but the stack has not been submitted yet
Run `gh stack submit` to push changes and recreate the stack on GitHub

Preflight checks

• I searched the existing issues for duplicates.
• I ran gh extension upgrade stack and reproduced this issue on the latest stable release.