G3: the focused cursor glides a jump on the Motion flavour's springs, and blinks

The core owns the motion, as Lift: animation.CursorGlide keeps the focused
cursor's four corners on springs (leading corners at the flavour's pace x2.4,
trailing ones x follow, so a jump smears and collapses; a long jump bows by
the flavour's arc), sampled at each frame's own time. A step of a cell or
less, insert mode, a focus change and any scroll (a file's view, a
terminal's output) land at once; a snap lands a glide under way too. The
quad is clamped to the focused pane when drawn (never its springs). Chrome
carries it on the wire (cursor_glide: bit 1 a cursor, bit 0 gliding;
cursor_alpha; cursor_quad, grid cells; cursor_idle_ms): the GUI draws the
quad as an overlay in the cursor's colour, at 85% (70% on the long
flavours) rising to solid as it lands, and hides the cells' cursors while it
does: one or the other every frame. Only the focused cursor glides.

Blink (CursorBlink, on by default in pixel shells) is the shell's: from
cursor_idle_ms and when the frame arrived, solid while typing and 500 ms
after, 530 ms halves with 80 ms eased edges, solid after 10 s idle, and
never while the window is unfocused or minimized or on a virtual clock. An
edge redraws the last frame with no core render (level B, blink_redraws);
an attached GUI blinks from the same field without a frame per edge.

Tests: snaps a cell, glides a jump with smear and bow, arrives under a pixel
by 150 ms on smooth and lands exactly, shifts with a scroll; blink holds,
eases, stops; the core glides a jump (ge) frame by frame (gliding exactly
while it moves, alpha rising, exact at rest), snaps a step (j) and a switch
to insert mid-glide; a terminal's scrolling output lands its cursor; wire
round-trip of the cursor record.

Shared files: src/animation.zig, src/pardes.zig, src/config.zig (toggle
CursorBlink), src/surface.zig, src/detached/wire.zig.

1 files changed, 10 insertions, 0 deletions

diff --git a/src/surface.zig b/src/surface.zig
index 15de128f..523cba43 100644
--- a/src/surface.zig
+++ b/src/surface.zig
@@ -412,6 +412,16 @@ pub const Chrome = struct {
     grip_focus_ring: [3]u8 = .{ 0, 0, 0 },
     /// A dirty pane's button fill.
     grip_dirty: [3]u8 = .{ 0, 0, 0 },
+    /// The focused cursor's quad (four corners, x then y, in grid cells, top
+    /// left clockwise): `cursor_glide` bit 1 says there is one, bit 0 that
+    /// it glides, when a pixel shell draws it at `cursor_alpha` in place of
+    /// its cursors (as it does while it blinks, from `cursor_idle_ms`, the
+    /// time since the last key or click when the frame was made; maxInt,
+    /// no blink).
+    cursor_glide: u8 = 0,
+    cursor_alpha: f32 = 1,
+    cursor_quad: [8]f32 = @splat(0),
+    cursor_idle_ms: u32 = std.math.maxInt(u32),
     /// The rule between a pane's tag and its body; null is halfway between
     /// the tag's ground and the page the shell actually draws.
     tag_rule: ?[3]u8 = null,