Window Resize on Coding Agents (eg. Claude Code or Gemini CLI)

[roromedia]

Describe the bug
Whenever you resize the window to a smaller size than the initial loading size, the terminal doesn't correctly reflow. This leads to double-lining and endless scrolling while typing. As soon as you enlarge the window over the initial size, this stops, but the prompt box isn't resized to the max-width of the window.

To Reproduce
Just resize window as mentioned above.

Expected behavior
It should reflow the contents and always max-width the prompt block. Terminals like Rio or Alacritty are doing this perfectly.

Desktop (please complete the following information):

• OS: MacOS Tahoe 26.1

Additional context
I tried to fork SwiftTerm and implement various reflow mechanisms but couldn't make it work. Seems there are more substantial or underlying changes needed.

[migueldeicaza]

Sounds like a task for Claude!

[tdrozdowski]

Add Junie to the list (Jetbrains) - not sure what's going on but I cannot get it to render properly in SwiftTerm at all. Claude works well for me (mostly) - so found this surprising.

[tdrozdowski]

I took a stab at this with Claude Code. No luck. I wound up rolling my project back to v1.5.0 and it behaves perfectly. So not entirely sure what changed between all of these (need to look more closely at all the commits) - but something did.

btw, 1.6.0 doesn't build cleanly as you have a dependency on a pre-release item that fails my build. I had to pin it to the git hash to get it to build. But then I ran into this issue so...back to no cut-n-paste, but the AI CLIs at least function (except for Junie - no idea what witchcraft their TUI is using to not work properly).

[roromedia]

I also tried with Claude Code before opening this issue - also no luck.
Alacritty which is a Rust-based terminal, as well as the new JetBrains terminals work well or at least better.

[migueldeicaza]

The 1.5.0 is a good data point

What’s the issue in 1.6.0, I should fix it

[tdrozdowski]

Here's the error I get: Dependencies could not be resolved because package 'swiftterm' is required using a stable-version but 'swiftterm' depends on an unstable-version package 'swift-subprocess' and root depends on 'swiftterm' 1.6.0.

On macOS 26.3 Beta + Xcode 26.2

[tdrozdowski]

FWIW - Claude's analysis on the diff between 1.5.0 and 1.6.0:

1. Commit 607674b (segment-based rendering) - This major refactor could have introduced subtle bugs in how column positions map during resize, especially for TUI apps that redraw on SIGWINCH.
2. Commit 91ef838 (yDisp removal) - The scroll offset calculation change could cause viewport tracking issues when TUI apps scroll their content.

[migueldeicaza]

Thanks for tracking these down, I’ll take a look soon

[migueldeicaza]

I am not sure I follow the problem, I started Codex, then resized the window and it is reflowing normally, so a series of screenshots showcasing the problem or a video would help.