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, 5 insertions, 2 deletions

diff --git a/src/detached/wire.zig b/src/detached/wire.zig
index b1b81eda..6e3b2d01 100644
--- a/src/detached/wire.zig
+++ b/src/detached/wire.zig
@@ -253,6 +253,8 @@ pub const Frame = struct {
             region.thumb_h = try r.getU16();
             region.notice = try r.getByte();
             region.clip = try r.getU16();
+            region.lift = @bitCast(try r.getU32());
+            if (!(region.lift >= 0 and region.lift <= 1)) return error.BadValue;
             if (region.rect.x > f.cols or region.rect.w > f.cols - region.rect.x or
                 region.rect.y > f.rows or region.rect.h > f.rows - region.rect.y or
                 region.clip > region.rect.w or region.thumb_y > region.rect.h or region.thumb_h > region.rect.h - region.thumb_y) return error.BadValue;
@@ -723,7 +725,7 @@ pub fn layersBound(layers: []const pardes.Layer, tags: []const pardes.Layer, reg
     return n + regions.len * region_len + chrome_len;
 }
 
-const region_len = 1 + 1 + 4 + 8 + 1 + 2 + 2 + 1 + 2;
+const region_len = 1 + 1 + 4 + 8 + 1 + 2 + 2 + 1 + 2 + 4;
 /// The palette: each colour three bytes, a theme's optional ones a flag
 /// before them.
 const chrome_len = @typeInfo(pardes.Chrome).@"struct".fields.len * 4;
@@ -807,6 +809,7 @@ pub fn encodeFrameLayers(out: []u8, cols: u16, rows: u16, cursor: ?Cursor, point
             try w.putU16(region.thumb_h);
             try w.putByte(region.notice);
             try w.putU16(region.clip);
+            try w.putU32(@bitCast(region.lift));
         }
         inline for (@typeInfo(pardes.Chrome).@"struct".fields) |field| {
             const rgb = @field(chrome, field.name);
@@ -1890,7 +1893,7 @@ test "detached wire carries compact body rows and exact pointer metrics" {
     var tag_cells: [3]pardes.Cell = @splat(.{});
     tag_cells[2] = logical[10];
     const tag: pardes.Layer = .{ .kind = .column, .id = 1, .viewport = .{ .x = 0, .y = 0, .w = 2, .h = 1 }, .cols = 3, .rows = 1, .bg = .{ 11, 22, 33 }, .cells = &tag_cells, .cursor = .{ .x = 2, .y = 0, .bar = true } };
-    const placed = [_]pardes.Region{.{ .kind = .rail, .owner = 3, .serial = 42, .rect = .{ .x = 0, .y = 1, .w = 2, .h = 3 }, .active = true, .thumb_y = 1, .thumb_h = 2, .clip = 1 }};
+    const placed = [_]pardes.Region{.{ .kind = .rail, .owner = 3, .serial = 42, .rect = .{ .x = 0, .y = 1, .w = 2, .h = 3 }, .active = true, .thumb_y = 1, .thumb_h = 2, .clip = 1, .lift = 0.5 }};
     const out = try gpa.alloc(u8, frameBound(2, 4) + layersBound(&.{layer}, &.{tag}, &placed));
     defer gpa.free(out);
     const palette: pardes.Chrome = .{ .page = .{ 1, 2, 3 }, .border = .{ 4, 5, 6 }, .tag_focus_bg = .{ 7, 8, 9 }, .scroll_thumb = .{ 10, 11, 12 } };