One Layer for tags, notices, headers and bodies; a taller tag is one layer of rows; wire v8

src/Layer.zig merges TagLayer and BodyLayer. `rows` (0 = no layer) and a
cursor at {x, y}. A tag of N rows is ONE layer of N grid rows: tagHit answers
the row as `line`, bodyHit keeps its meaning, and the per-line layer bases
(TAG_LINE_LAYER_BASE, HEADER_LINE_LAYER_BASE) are gone, not aliased.

Wire v8, the one bump: tag layers carry rows and cursor y, and the frame
carries the placed region list. v7 and v9 peers are refused in both
directions (server test over both, a new frontend test over both).

web: tag_layer_value 11 = rows, 12 = cursor y; app.mjs lays every row.
macOS: the Zig side compiles against Layer; pardes.h still sees one row
per tag layer (accepted, the macOS shell is ignored for now).

No visual change: snapshot goldens and the 17 GUI goldens byte-identical.

Shared files touched: pardes.zig, Messages.zig, gui.zig, macos.zig,
detached/client.zig, detached/server.zig, detached/wire.zig (plus web.zig,
app.mjs, edit.zig, look.zig). Not touched: mouse.zig, tagline.zig,
colors.zig, tty.zig, dump.zig, exec.zig, host_io.zig, panes.zig.

1 files changed, 7 insertions, 8 deletions

diff --git a/src/surface.zig b/src/surface.zig
index fec43e30..db7dd468 100644
--- a/src/surface.zig
+++ b/src/surface.zig
@@ -11,8 +11,7 @@ const config = @import("config.zig");
 const pdf_enabled = panes.Pdf.enabled;
 const image = @import("image.zig");
 const MAX_PANES = pardes.MAX_PANES;
-const BodyLayer = @import("body_layer.zig").Layer;
-const TagLayer = @import("tag_layer.zig").Layer;
+const Layer = @import("Layer.zig");
 const MAX_TAG_LAYERS = pardes.MAX_TAG_LAYERS;
 const CellPixels = pardes.CellPixels;
 
@@ -380,8 +379,8 @@ pub const Surface = struct {
     /// paint the quiet affordance can carry the hover bit through the ABI
     /// without every selection painter learning a new parameter.
     mark_hover: bool = false,
-    body_layers: [MAX_PANES]BodyLayer = @splat(.{}),
-    tag_layers: [MAX_TAG_LAYERS]TagLayer = @splat(.{}),
+    body_layers: [MAX_PANES]Layer = @splat(.{}),
+    tag_layers: [MAX_TAG_LAYERS]Layer = @splat(.{}),
     cols: u16 = 0,
     rows: u16 = 0,
     regions: [MAX_REGIONS]Region = undefined,
@@ -394,15 +393,15 @@ pub const Surface = struct {
     panel_tracks: [MAX_PANES * 2]animation.Track = undefined,
     npanel_tracks: usize = 0,
     previous_cells: []const Cell = &.{},
-    previous_body_layers: []const BodyLayer = &.{},
-    previous_tag_layers: []const TagLayer = &.{},
+    previous_body_layers: []const Layer = &.{},
+    previous_tag_layers: []const Layer = &.{},
     cell_diffs: []const PanelCellDiff = &.{},
 
-    pub fn tagLayers(s: *const Surface) []const TagLayer {
+    pub fn tagLayers(s: *const Surface) []const Layer {
         return &s.tag_layers;
     }
 
-    pub fn bodyLayers(s: *const Surface) []const BodyLayer {
+    pub fn bodyLayers(s: *const Surface) []const Layer {
         return &s.body_layers;
     }