Turn ligatures off with a Ligatures setting, in the shell that shapes text

The SDL shell shapes words with HarfBuzz, so a font's `->` and `!=` draw as
ligatures, and there was no way to have the plain glyphs back short of
changing font. `Ligatures` is a toggle, on by default; off, no cell goes to
the shaper and every cell draws its own glyph, exactly as a font without
ligatures does.

It exists only where it means something. A new `ligatures` capability, true
for the gui shell alone, gates it like Font and WindowOpacity are gated: it is
not a builtin elsewhere, has no leader path, and Config does not list it,
rather than print a row the TTY could never change. macOS draws CoreText
ligatures of its own, but nothing there reads the setting, so it stays off
there. The table check that kept every toggle unconditional now lets the
ligatures toggle, and only it, carry a capability, and requires that it
carry `ligatures`; every other setting's rule is as it was.

The gui keeps the setting beside its text caches, which were resolved under
it: when the core's value changes, the per-codepoint cells (which record
whether a cell is shaped) and the shaped words are dropped, and the frame the
toggle asked for draws every cell again. The atlas keeps its glyphs: plain
ones draw either way, and a ligature's strip is reused when it comes back.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

1 files changed, 13 insertions, 4 deletions

diff --git a/docs/config.md b/docs/config.md
index d1cc2e6e..9c51f329 100644
--- a/docs/config.md
+++ b/docs/config.md
@@ -25,16 +25,19 @@ which `Config` reports as `no per-user config path`.
 `+Config` pane. It reports the startup path and every live config-like value:
 theme, colors, focus tint, syntax weight, wrapping, tag position, debug mode, the requested shell and the
 executable actually resolved at the last spawn, requested/effective GUI font
-and size, tagline scale, window opacity, panel transition,
+and size, tagline scale, window opacity, ligatures (SDL GUI only), panel transition,
 scene effects, hover delay, platform, native-image support, and (on SDL) whether
 the executable uses live-built shaders or the paired prebuilt shader snapshot.
 Platform-dependent rows say `unsupported` instead of looking like an off or
-empty supported setting. The five fields of `config.Runtime.Capabilities` gate
+empty supported setting. The fields of `config.Runtime.Capabilities` gate
 them and are stated once as plain data in `builtins.capabilities`:
 `font_picker` is the SDL GUI and
 native macOS only, `scene_shaders` the same two, `panel_transitions` every
-hosted shell, `window_opacity` the SDL GUI only, and `tagline_font_size`
-everything but the TTY and the board. So
+hosted shell, `window_opacity` the SDL GUI and macOS, `window_blur` macOS
+only, `ligatures` the SDL GUI only, and `tagline_font_size`
+everything but the TTY and the board. `ligatures` is the exception to
+`unsupported`: where it is off, `Ligatures` is not a builtin at all and
+`Config` has no row for it. So
 the TTY reports Font, TaglineSize and the scene shaders as unsupported; the
 browser reports Font, panel transitions and the scene shaders as unsupported,
 and its TaglineSize row reads `82 (build-time only)` — tagline font size is
@@ -133,6 +136,12 @@ the current value. A `FocusTint` line in a fresh startup configuration disables
 the tint; a `SyntaxBold` line enables the stronger keyword weight. Those two
 appearance controls leave focus, selections and editing behavior unchanged.
 
+`Ligatures` (SDL GUI only) toggles a font's programming ligatures, such as
+Maple Mono's `->` and `!=` drawn across their cells; it is on by default.
+Off, every cell draws its own glyph, exactly as a font without ligatures does.
+`Ligatures on` and `Ligatures off` set it explicitly. The native macOS shell
+draws CoreText ligatures of its own, which this setting does not reach.
+
 `TreeContext` toggles sticky declaration headers for the current source pane.
 It is off by default and appears in the default pane tag when a tree-sitter
 grammar supports that file. `TreeContext on` and `TreeContext off` set it