Fit Ghostty windows to terminal rows and remove the tmux bottom gap

[akan72]

Summary

A pixel-sized Ghostty window can leave unused space below its last complete terminal row. Extending the tmux Powerline backgrounds into that space produces rectangular tails; coloring the space with the terminal background leaves a dark strip instead.

Use regular windows sized in terminal cells, zero vertical padding, and native cell-step resizing. Hide the native titlebar/tab bar so it cannot consume a fractional number of rows after initial sizing. Start fresh windows at 120 × 32 cells, make the verified 18-point font explicit, and disable restoring old pixel-sized frames so they cannot bring the gap back on launch. Keep padding background neutral so any remaining horizontal space does not distort the separators.

This deliberately uses regular row-fitted windows rather than forced full-screen/maximized pixel rectangles, which can recreate a remainder. The native window buttons and tab bar are hidden; tmux provides the tabs. Apply through a fresh window because Ghostty 1.2.3 retains old padding-extension flags after reload. The exact config is installed locally, and a working fresh window is left open.

Test Plan

• Passed /Applications/Ghostty.app/Contents/MacOS/ghostty +validate-config --config-file=/private/tmp/ghostty-powerline-fix/ghostty/config and validation of the installed symlinked config; passed git diff --check and the commit's secret check.
• Launched the actual saved config with open -na /Applications/Ghostty.app --args -e /opt/homebrew/bin/tmux attach-session -t 0. The final fresh-launch test uses no font, padding, titlebar, grid-size, or save-state CLI overrides; all layout settings come from the saved config.
• Captured real windows with screencapture -x -o -l3437 and screencapture -x -o -l3406, excluding macOS shadows and cropping only their bottom 100 pixels. The matched crops are both 2656 × 100, use the same tmux session/window and 18-point font, and show the intended window-layout change.
• Ran python3 /private/tmp/ghostty-padding-evidence.lXWGTH/verify-gap-images.py: the center 48-pixel Powerline segment is pixel-identical after its vertical move. Before, a 24-pixel dark strip follows the status row; after, the row reaches the bottom edge with no dark strip or colored tails. The regular-window regression case reproduces the gap caused by native tab chrome; it is not merely a color comparison.
• Confirmed the config-driven window is 120 × 32 cells with 22 × 48-pixel cells and a 2656 × 1536-pixel window. Also launched --window-height=31 --window-width=118; its 1488-pixel height equals 31 × 48 and its bar also reaches the bottom edge.
• Uploaded both PNGs as GitHub attachments; verified SHA-256, image decoding, and their rendered PR table. Only ghostty/config appears in the branch's changed files and commit history; generated screenshots are not committed.
• All eight CI checks passed on final commit 2c2ceb4: static checks, pre-commit, Actions security, secret history, macOS installation, Ubuntu installation, and both VPS installation targets.

Before — native tab chrome leaves a bottom gap	After — fff912f, row-fitted window

Fresh launch from the final saved config (2c2ceb4), with no layout overrides. The window is 2656 × 1536 pixels, the grid is 120 × 32 cells at 22 × 48 pixels per cell, and status colors reach the final scanline with no terminal-background strip: