The Canvas renderer's font stack only listed regular monospace faces,
so powerline separators, devicons, and other private-use prompt glyphs
rendered as missing characters. Append locally installed Nerd Font and
Powerline symbol faces as glyph-only fallbacks behind the existing
faces; cell metrics still come from the primary monospace fonts.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>