Route ghostty Bold ASCII to Menlo instead of BIZ UDGothic Bold

[ikuwow]

Context

xdg-config/ghostty/config currently pins the CJK fallback to BIZ UDGothic Bold:

font-family = "Monaco"
font-family = "BIZ UDGothic Bold"

This resolves the previously observed instability where CJK codepoints (notably の) rendered inconsistently after display switches — a symptom of ghostty's runtime font discovery on macOS 26.5. Reference: ghostty-org/ghostty#12916, #8712, #707.

Finding

Bold ASCII characters (SGR 1, terminal emphasis) are now drawn by BIZ UDGothic Bold's Latin glyphs, not by Monaco.

Inferred mechanism (not verified against ghostty source):

• Monaco has only a Regular face. system_profiler SPFontsDataType confirms Style: Regular is the only variant in the Monaco family.
• When ghostty needs a Bold ASCII glyph, its per-codepoint face selection walks the fallback chain for a face that covers the codepoint at the requested Bold weight.
• Monaco Regular has no Bold face. BIZ UDGothic Bold has Bold weight plus full ASCII coverage (verified via CoreText CTFontCopyCharacterSet). Ghostty picks it for Bold ASCII.
• This matches the pre-pin "original" appearance — ghostty's cold discovery was picking BIZ UDGothic Bold all along, so Bold ASCII was already routed through it. The explicit pin just made it stable.

Proposal

Route Bold ASCII to a Monaco-lineage successor so the Latin personality stays consistent across weights.

font-family = "Monaco"
font-family-bold = "Menlo"
font-family = "BIZ UDGothic Bold"

Rationale for Menlo:

• Menlo is the de-facto Monaco successor on macOS (Bitstream Vera Sans Mono derivative), letterform DNA is close
• Preinstalled with Regular / Bold / Italic / Bold Italic
• Ghostty has explicit font-family-bold / font-family-italic / font-family-bold-italic style knobs (ghostty +show-config --default --docs)

SF Mono is out of scope: it is not installed by default on macOS (bundled inside Terminal.app, requires manual extraction).

Follow-ups to verify before implementing

• Confirm font-family-bold = "Menlo" actually redirects Bold ASCII rendering with a multi-line font-family cascade (ghostty style override interaction against fallback chain is not documented in a single spot; needs empirical test)
• Confirm Bold CJK stays on BIZ UDGothic Bold (ghostty +show-face --string="のＡ" --style=bold)
• Consider font-family-italic = "Menlo" for the same personality-continuity reason

Notes learned during investigation

• ghostty +show-face reports only the family name, not the specific face/weight. Two families with the same name but different weights are indistinguishable in its output.
• ghostty +list-fonts shows only monospace-eligible fonts; proportional CJK families (Hiragino Sans, BIZ UDGothic) are hidden from that listing but still available for font-family.
• Morisawa Fonts image search (fontsjourney.morisawafonts.com, free without subscription) matched the rendered CJK against TBUD Gothic Std B / TBUD 丸ゴシック Std B. TBUD Gothic is what BIZ UDGothic is the OFL public release of (designed by Type Bank Co. and Morisawa Inc., per Google Fonts specimen).
• The CoreText default cascade from Monaco returns Hiragino Sans W3 as the first CJK face, not BIZ UDGothic. Ghostty's own discovery differs from CoreText's default cascade.