auto cover style: use sextants when fontconfig has a font with the glyphs

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/ui/cover.go

@@ -8,6 +8,7 @@ import (
 	"image/color"
 	_ "image/jpeg" // poster formats
 	_ "image/png"
+	"os/exec"
 	"strings"
 	"time"
 
@@ -138,9 +139,29 @@ func coverStyleFor(setting string, env func(string) string) coverStyle {
 	if env("KITTY_WINDOW_ID") != "" || env("WEZTERM_PANE") != "" {
 		return sextantStyle
 	}
+	// Other terminals (GNOME Terminal, Konsole, Alacritty...) draw glyphs their
+	// font lacks from a fallback font, so sextants work if some installed font
+	// has them. Over SSH the installed fonts are the remote machine's, which
+	// says nothing about the terminal, so keep the safe style there.
+	if env("SSH_CONNECTION") == "" && env("SSH_TTY") == "" && sextantFontAvailable() {
+		return sextantStyle
+	}
 	return quadrantStyle
 }
 
+// sextantFontAvailable reports whether fontconfig knows a font with the
+// sextant characters. It is a variable so tests can replace it.
+var sextantFontAvailable = func() bool {
+	path, err := exec.LookPath("fc-list")
+	if err != nil {
+		return false
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+	out, err := exec.CommandContext(ctx, path, ":charset=1fb00", "family").Output()
+	return err == nil && len(bytes.TrimSpace(out)) > 0
+}
+
 // resolveCovers decides how posters are drawn: as real images through the
 // Kitty graphics protocol (graphics) or with block characters in the given
 // style. "kitty" asks for the protocol explicitly; "auto" uses it when the