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.

2 files changed, 21 insertions, 19 deletions

diff --git a/test/column_drag.zig b/test/column_drag.zig
index feea1bf7..3aea4286 100644
--- a/test/column_drag.zig
+++ b/test/column_drag.zig
@@ -8,17 +8,17 @@ fn mouse(p: *Pardes, kind: pardes.Mouse.Kind, col: u16) void {
     p.update(.{ .mouse = .{ .button = .left, .kind = kind, .col = col, .row = pardes.TOPBAR_H } });
 }
 
-fn tagLayer(p: *Pardes, column: usize) !*pardes.TagLayer {
+fn tagLayer(p: *Pardes, column: usize) !*pardes.Layer {
     for (&p.surface.tag_layers) |*layer| {
-        if (layer.cols > 0 and layer.kind == .column and layer.id == column) return layer;
+        if (layer.rows > 0 and layer.kind == .column and layer.id == column) return layer;
     }
     return error.MissingColumnTagLayer;
 }
 
-fn headerMouse(layer: *const pardes.TagLayer, display_col: u16, kind: pardes.Mouse.Kind) pardes.Mouse {
+fn headerMouse(layer: *const pardes.Layer, display_col: u16, kind: pardes.Mouse.Kind) pardes.Mouse {
     const x = @as(f32, @floatFromInt(layer.viewport.x)) * 10 + (@as(f32, @floatFromInt(display_col)) + 0.5) * 5;
     const y = (@as(f32, @floatFromInt(layer.viewport.y)) + 0.5) * 20;
-    return .{ .button = .left, .kind = kind, .col = @intFromFloat(x / 10), .row = @intFromFloat(y / 20), .tag_hit = layer.hitAt(x, y, 10, 20, 5, 10) };
+    return .{ .button = .left, .kind = kind, .col = @intFromFloat(x / 10), .row = @intFromFloat(y / 20), .tag_hit = layer.tagHit(x, y, 10, 20, 5, 10) };
 }
 
 const Snapshot = struct {
@@ -144,7 +144,7 @@ test "column grip is separate from compact text and the resize seam" {
         try std.testing.expectEqual(p.col_x[column], rect.x);
         try std.testing.expectEqual(rect.x + pardes.TAG_TEXT_INSET, (try tagLayer(p, column)).viewport.x);
         for (p.surface.tagLayers()) |pane_layer| {
-            if (pane_layer.cols > 0 and pane_layer.kind == .pane and pane_layer.id == pane_id)
+            if (pane_layer.rows > 0 and pane_layer.kind == .pane and pane_layer.id == pane_id)
                 try std.testing.expectEqual((try tagLayer(p, column)).viewport.x, pane_layer.viewport.x);
         }
         const pane_tag_y = if (p.settings.tag_bottom) rect.y + rect.h - pardes.BOX_H else rect.y;
diff --git a/test/panes.zig b/test/panes.zig
index 11fb750a..5e26cdd0 100644
--- a/test/panes.zig
+++ b/test/panes.zig
@@ -19,17 +19,17 @@ fn setTag(pane: *Pane, text: []const u8) !void {
 }
 
 const TagLayerTests = struct {
-    const Kind = @FieldType(pardes.TagLayer, "kind");
-    fn findLayer(p: *Pardes, kind: Kind, id: usize) !*pardes.TagLayer {
+    const Kind = @FieldType(pardes.Layer, "kind");
+    fn findLayer(p: *Pardes, kind: Kind, id: usize) !*pardes.Layer {
         for (&p.surface.tag_layers) |*layer| {
-            if (layer.cols > 0 and layer.kind == kind and layer.id == id) return layer;
+            if (layer.rows > 0 and layer.kind == kind and layer.id == id) return layer;
         }
         return error.MissingTagLayer;
     }
 
-    fn mouse(layer: *const pardes.TagLayer, x: f32, kind: pardes.Mouse.Kind) pardes.Mouse {
+    fn mouse(layer: *const pardes.Layer, x: f32, kind: pardes.Mouse.Kind) pardes.Mouse {
         const y = (@as(f32, @floatFromInt(layer.viewport.y)) + 0.5) * 20;
-        return .{ .button = .left, .kind = kind, .col = @intFromFloat(x / 10), .row = @intFromFloat(y / 20), .tag_hit = layer.hitAt(x, y, 10, 20, 5, 10) };
+        return .{ .button = .left, .kind = kind, .col = @intFromFloat(x / 10), .row = @intFromFloat(y / 20), .tag_hit = layer.tagHit(x, y, 10, 20, 5, 10) };
     }
 
     test "compact tag layers render and edit Unicode text beyond body column capacity" {
@@ -200,14 +200,16 @@ test "a tag with a newline in it is as tall as its lines, and each line is typed
         const body_y = p.bodyTop(pane, r);
         try std.testing.expectEqual(if (bottom) r.y else r.y + 2, body_y);
         try std.testing.expectEqualStrings("b", surface.at(r.x + config.GUTTER + panes.File.gutterWidth(pane), body_y).grapheme());
-        // a layer to a line, for a pixel shell
-        var lines: usize = 0;
+        // one layer, a row to each line, for a pixel shell
+        var layers: usize = 0;
         for (p.surface.tagLayers()) |*layer| {
-            if (layer.cols == 0 or layer.kind != .pane or layer.id != 0) continue;
-            try std.testing.expectEqual(tag_y + layer.line, layer.viewport.y);
-            lines += 1;
+            if (layer.rows == 0 or layer.kind != .pane or layer.id != 0) continue;
+            try std.testing.expectEqual(tag_y, layer.viewport.y);
+            try std.testing.expectEqual(@as(u16, 2), layer.rows);
+            try std.testing.expectEqual(@as(u16, 2), layer.viewport.h);
+            layers += 1;
         }
-        try std.testing.expectEqual(@as(usize, 2), lines);
+        try std.testing.expectEqual(@as(usize, 1), layers);
         // a click on the second line puts the tag's cursor on it
         p.update(.{ .key = .{ .cp = Key.escape } });
         p.update(.{ .key = .{ .cp = ':' } });
@@ -541,11 +543,11 @@ const TagNavigationTests = struct {
 };
 
 const BodyHitTests = struct {
-    fn mouse(layer: *const pardes.BodyLayer, row: u16, col: u16, kind: pardes.Mouse.Kind) pardes.Mouse {
+    fn mouse(layer: *const pardes.Layer, row: u16, col: u16, kind: pardes.Mouse.Kind) pardes.Mouse {
         const width: f32 = if (row < layer.context_rows) 8 else 10;
         const x = @as(f32, @floatFromInt(layer.viewport.x)) * 10 + (@as(f32, @floatFromInt(col)) + 0.5) * width;
         const y = layer.rowTop(row, 20, 10) + layer.rowHeight(row, 20, 10) / 2;
-        return .{ .button = .left, .kind = kind, .col = @intFromFloat(x / 10), .row = @intFromFloat(y / 20), .body_hit = layer.hitAt(x, y, 10, 20, 8, 10).? };
+        return .{ .button = .left, .kind = kind, .col = @intFromFloat(x / 10), .row = @intFromFloat(y / 20), .body_hit = layer.bodyHit(x, y, 10, 20, 8, 10).? };
     }
 
     test "compact TreeContext mouse follows source rows in reclaimed space" {
@@ -673,7 +675,7 @@ const TreeContextTests = struct {
             const y = layer.rowTop(row, 20, 10) + 9.5;
             const x = @as(f32, @floatFromInt(layer.viewport.x)) * 10 + 5;
             // A one-pixel separator remains inside its existing header row.
-            try std.testing.expectEqual(row, layer.hitAt(x, y, 10, 20, 8, 10).?.row);
+            try std.testing.expectEqual(row, layer.bodyHit(x, y, 10, 20, 8, 10).?.row);
         }
         pane.scrollBy(-5);
         _ = try p.render(frame.allocator());