[lvanhouten]

FitAddon sizes rows and cols from the computed height and width of xterm's parent element. .terminal-pane is border-box with 8px padding, so those values included 16px the terminal could not use. Fit could then add a row that overflowed the pane and got cut off at the bottom, plus up to two columns past the right edge.

Use an 8px margin instead of padding so fit measures only the space xterm can draw in. The gutter looks the same.

What changed

Two CSS changes in TerminalPane.css that fix how the terminal fills its pane:

1. .terminal-pane: padding: 8px → margin: 8px. FitAddon sizes rows and columns from the computed border-box of xterm's parent. With box-sizing: border-box and padding, that counted 16px the terminal couldn't use, so fit often added a row that overflowed the pane and was clipped at the bottom, plus up to two columns past the right edge. A margin keeps the same gutter while fit measures only the space xterm can draw in.

2. .xterm-viewport background → var(--tempest-bg-editor). xterm.css paints .xterm-viewport #000, and xterm 6 applies the theme background only to the scrollable element that spans the rows. Rows rarely fill the pane exactly, so a strip up to one row high is left below the last row. Without the overflowing row from (1) covering it, that strip showed as a black bar. The viewport now uses the same color as the terminal theme, so it follows theme changes.

Splitting the gutter between padding and margin doesn't avoid either problem. Over 60 pane heights, padding: 4px; margin: 4px clipped the last row at 16 and showed the black strip at 24, so both changes are needed.

Related issue

N/A

How was this tested

• Harness (xterm 6.0.0 + addon-fit 0.11.0, same DOM and CSS as TerminalPane), across 60 pane heights:

  	Last row clipped	Black strip below last row
  Before	32 / 60 (up to 8px)	-
  After	0 / 60	0 / 60

  Column count also drops from 81 to 79, the correct value.

• Same harness in Playwright WebKit 26.6 (the macOS engine family): identical results.

• Installed build on Windows 11: Claude Code's bottom status line, which used to be half cut off, now renders fully, with no bar below it.

Checklist

• npx tsc --noEmit passes
• cargo check passes (if backend changed) - N/A, CSS only
• I've tested this on my OS — noted which: Windows 11
• Docs updated if user-facing behaviour changed - N/A
• No secrets, tokens, or personal paths in the diff

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[gsvprharsha]

@lvanhouten Thank you so much for the PR. We have merged it into the main branch