ghostty-web sized a cell at ceil(measureText("M").width) — always the next whole pixel up — so libghostty cells ran ~1px (~10%) wider than the glyph advance and did not line up with xterm. Shim the renderer's measureFont in the adapter to round the advance to the nearest pixel instead (keeping upstream height/baseline). Also await document.fonts.ready before the renderer first measures: ghostty measures once at open() and never remeasures, so with the async swap webfont it could otherwise lock the fallback font's advance. Both are adapter-only shims; ghostty-web exposes no cell-width knob. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01GBWyw3DyRvvNmgJpFZBsC5