fix(markdown-compose): measure table cells by display width

[sinelaw]

Summary

In Markdown compose/preview mode, the right border of a rendered table is drawn one column too far right on any row whose last cell ends in a 2-cell-wide glyph (emoji such as ✅, CJK, …). Because the current (cursor) line is rendered raw and stays correctly aligned, the border appears to flicker/pop as the cursor moves over each emoji row. Rows without a wide trailing glyph are unaffected. Fixes #2475.

Root cause

The markdown_compose plugin measured cell text with JS String.length (UTF-16 code units), so ✅ (U+2705) counted as 1 column while the renderer lays it out as 2. Non-cursor rows were therefore padded one column too wide, pushing their right │ past the ┌┐└┘├┼┤ box frame.

Fix

Add a small displayWidth() helper backed by editor.stringWidth — the plugin API added in #2401, itself backed by fresh_core::display_width — so the plugin measures cells exactly as the editor lays out terminal cells. Routed the four width-measuring sites through it:

• column max-width in processTableAlignment
• cell padding width
• the truncation overflow check
• the wrapped-cell padding

// Terminal column width (wide glyphs = 2), matching the renderer's layout.
function displayWidth(text: string): number {
  return editor.stringWidth(text);
}

Verification

Reproduced and verified in tmux (110×30, xterm-256color) with the example file from #2475:

• Before: emoji rows draw their right border at column 45 (protruding) except the cursor's row at 44.
• After: every emoji row sits at column 44 — flush with the box — at all cursor positions (Ln1–Ln18); no misalignment, no pop. The no-emoji control table is unchanged.

Plugin type checks pass (plugins/check-types.sh).

Related

• Expose core unicode display-width to plugins (charWidth/stringWidth) #2401 — exposes editor.charWidth / editor.stringWidth to plugins (the API this fix uses).
• Skip synchronized-update markers inside tmux (fixes stray glyphs on scroll) #2400 — skips synchronized-update markers inside tmux; addresses the scroll/stray-glyph facet of the same Markdown preview: table right border flickers/misaligns while scrolling on rows ending in an emoji #2475 report. This PR is complementary: it fixes the underlying cell-width miscalculation.

🤖 Generated with Claude Code