G1: Lift, soft elevation shadows (off by default)

`Lift` (a GUI toggle, capability lift) lifts the focused pane on a
critically damped spring (animation.Spring: closed form, about 240 ms to
settle, velocity kept across retargets, settled = no frames) and floats
notices. The core puts the lift on the regions (Region.lift, on the wire);
the GUI casts from it: a soft shadow is decor, an erf rectangle on one
quad grown by 3 sigma (decor.frag, flag 0x10000000), in the quad's own
space so a track's transform carries it; darken-only, the caster's rect
left alone, alpha pre-warped for linear light and IGN-dithered. Cast last
in its group, so a neighbour's rails and rules darken with its text; a
notice's before its rule. Strength is capped per theme so text over the
darkest shadow keeps min(its contrast, 4.5) (test over the native themes).

Opt-in until the focus lift/dim default is decided. Feel review material:
docs/effects.md. Test-mode PARDES_TEST_SERIES keeps every captured frame.

Shared files touched: pardes.zig (two fields, one nextWake line),
detached/wire.zig (lift on the region), config.zig, builtins.zig
(capability), gui.zig. Not touched: Messages.zig, mouse.zig, tty,
host_io.

1 files changed, 14 insertions, 4 deletions

diff --git a/src/config.zig b/src/config.zig
index 186b29a1..0ed8726a 100644
--- a/src/config.zig
+++ b/src/config.zig
@@ -115,6 +115,7 @@ pub const leader_path = paths: {
     if (builtins.capabilities.window_opacity) table.set(.WindowOpacity, null);
     if (builtins.capabilities.window_blur) table.set(.WindowBlur, null);
     if (builtins.capabilities.ligatures) table.set(.Ligatures, null);
+    if (builtins.capabilities.lift) table.set(.Lift, null);
     if (builtins.capabilities.panel_transitions) {
         table.set(.PanelSlide, "as");
         table.set(.PanelZoom, "az");
@@ -618,6 +619,10 @@ pub const Runtime = struct {
     /// A font's programming ligatures (`->`, `!=`) draw across their cells.
     /// Only a shell that shapes text has the setting (`Capabilities.ligatures`).
     ligatures: bool = true,
+    /// The focused pane and the notices stand off the page on soft shadows
+    /// (G1, docs/render-pipeline.md §9.1). Opt-in until the focus lift's
+    /// default is decided. Only a pixel shell draws it (`Capabilities.lift`).
+    lift: bool = false,
     /// Builtins announce themselves on the message row.
     verbose: bool = true,
     /// A message falls into its row and dissolves out of it.
@@ -808,6 +813,8 @@ pub const Runtime = struct {
         window_blur: bool = false,
         /// The shell shapes text, so it can draw ligatures and stop drawing them.
         ligatures: bool = false,
+        /// The shell draws soft shadows under what stands off the page.
+        lift: bool = false,
     };
 
     pub const Capability = std.meta.FieldEnum(Capabilities);
@@ -815,7 +822,7 @@ pub const Runtime = struct {
     /// The message timings a setting word sets, each in milliseconds.
     pub const MessageTime = enum { linger, fall, dissolve };
 
-    pub const Toggle = enum { colors, wrap, tree_context_tag_style, tag_bottom, debug, focus_tint, column_tags, syntax_bold, verbose, message_animation, ligatures };
+    pub const Toggle = enum { colors, wrap, tree_context_tag_style, tag_bottom, debug, focus_tint, column_tags, syntax_bold, verbose, message_animation, ligatures, lift };
     /// The bundled post pass, a Shadertoy file in shaders/post/.
     pub const Scene = enum { crt };
 
@@ -863,6 +870,7 @@ pub const Runtime = struct {
         .{ .word = "Verbose", .action = .{ .toggle = .verbose } },
         .{ .word = "MessageAnimation", .action = .{ .toggle = .message_animation } },
         .{ .word = "Ligatures", .action = .{ .toggle = .ligatures }, .availability = .ligatures },
+        .{ .word = "Lift", .action = .{ .toggle = .lift }, .availability = .lift },
         .{ .word = "MessageLinger", .action = .{ .message_ms = .linger } },
         .{ .word = "MessageFall", .action = .{ .message_ms = .fall } },
         .{ .word = "MessageDissolve", .action = .{ .message_ms = .dissolve } },
@@ -924,9 +932,9 @@ pub const Runtime = struct {
                     @compileError("scene effects must use the scene-shader capability"),
                 // A toggle is plain state any shell can hold, except one for
                 // what only some shells draw: that one exists where they do.
-                .toggle => |field| if (field == .ligatures) {
-                    if (setting.availability != .ligatures)
-                        @compileError("the ligatures toggle must use the ligatures capability");
+                .toggle => |field| if (field == .ligatures or field == .lift) {
+                    if (setting.availability == null or !std.mem.eql(u8, @tagName(setting.availability.?), @tagName(field)))
+                        @compileError("a pixel shell's toggle must use its own capability: " ++ @tagName(field));
                 } else if (setting.availability != null)
                     @compileError("unconditional toggles cannot carry a backend capability"),
                 else => if (setting.availability != null)
@@ -1447,6 +1455,7 @@ pub const Runtime = struct {
                 .window_opacity = true,
                 .window_blur = true,
                 .ligatures = true,
+                .lift = true,
             },
             .state = &state,
         };
@@ -1485,6 +1494,7 @@ pub const Runtime = struct {
                     .verbose => "Verbose off\n",
                     .message_animation => "MessageAnimation off\n",
                     .ligatures => "Ligatures off\n",
+                    .lift => "Lift on\n",
                 },
                 .shell => "Shell requested (new panes) fish\n",
                 .tagline_size => "TaglineSize 73\n",