Buffer.Resize truncates/drops cells with no reflow, permanently losing content on shrink+grow

[muhamm-ad]

ultraviolet.Buffer.Resize (buffer.go) truncates/drops cells on shrink with no reflow and nothing preserved:

func (b *Buffer) Resize(width int, height int) {
    ...
    } else if width < curWidth {
        for i := range b.Lines {
            b.Lines[i] = b.Lines[i][:width] // cells beyond width: gone
        }
    }
    ...
    } else if height < len(b.Lines) {
        b.Lines = b.Lines[:height] // rows beyond height: gone
    }
}

Consequences downstream in charmbracelet/x/vt's Emulator.Resize (which calls straight into this for both the main and alt screens):

• Shrinking width truncates every row to the new width; the trailing cells are discarded, not wrapped onto a new row and not pushed to scrollback.
• Shrinking height keeps rows [0, newHeight) and drops [newHeight, oldHeight), i.e. it drops the bottom rows, not the top ones a terminal would normally scroll into history.
• Growing back afterwards only appends blank cells / blank rows, there's nothing left to restore from, so previously-visible content never comes back even though there's room for it again.

Repro

Using vt.NewEmulator directly (no PTY needed):

term := vt.NewEmulator(10, 1)
term.WriteString("0123456789")
term.Resize(5, 1)   // "56789" is now gone
term.Resize(10, 1)  // still gone, row is "01234     "

Expected

At minimum, don't silently discard already-rendered content, e.g. push truncated/dropped cells to the emulator's scrollback (same as Screen.ClearWithScrollback already does on erase) so it's recoverable via scrollback even if live reflow is out of scope. Ideally, real reflow: recompute line wrapping from a logical-line model in both directions, the way terminals like Windows Terminal/iTerm2/kitty do.

Where I hit this

Building an SSH-in-a-TUI pane on top of x/vt (https://github.com/muhamm-ad/bubble-ssh), resizing the pane (e.g. resizing the host terminal window) permanently loses on-screen content that falls outside the new size, and growing back doesn't recover it.

Versions

• github.com/charmbracelet/ultraviolet, confirmed present in v0.0.0-20260703014108-f5a850f9c2b7 and still present in the latest available commit as of 2026-09-07, v0.0.0-20260906173415-0277a179edd9.
• github.com/charmbracelet/x/vt, same, v0.0.0-20260730164118-7e2d3e6c5238 through v0.0.0-20260906004030-3986e9119cf9.