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, 6 insertions, 6 deletions

diff --git a/src/Presentation.zig b/src/Presentation.zig
index 45b196c8..e1f1b585 100644
--- a/src/Presentation.zig
+++ b/src/Presentation.zig
@@ -42,8 +42,8 @@ shown_closing_len: usize = 0,
 acknowledged: bool = false,
 pending: bool = false,
 previous_cells: []pardes.Cell = &.{},
-previous_body_layers: [MAX_PANES]pardes.BodyLayer = @splat(.{}),
-previous_tag_layers: [pardes.MAX_TAG_LAYERS]pardes.TagLayer = @splat(.{}),
+previous_body_layers: [MAX_PANES]pardes.Layer = @splat(.{}),
+previous_tag_layers: [pardes.MAX_TAG_LAYERS]pardes.Layer = @splat(.{}),
 previous_cols: u16 = 0,
 previous_rows: u16 = 0,
 previous_valid: bool = false,
@@ -335,7 +335,7 @@ pub fn capturePrevious(self: *Presentation, gpa: std.mem.Allocator, surface: *co
         old.cells = storage;
     }
     for (&self.previous_tag_layers, surface.tagLayers()) |*old, *current| {
-        const count = if (current.cols > 0) current.cells.len else 0;
+        const count = if (current.rows > 0) current.cells.len else 0;
         const storage = if (old.cells.len == count) old.cells else gpa.realloc(old.cells, count) catch {
             self.previous_valid = false;
             self.previous_layout = @splat(null);
@@ -684,7 +684,7 @@ test "presentation submission failure preserves shown geometry until retry is ac
 }
 
 test "fractional panel inverse preserves compact header rows through slide and zoom" {
-    const layer: pardes.BodyLayer = .{ .serial = 7, .viewport = .{ .x = 4, .y = 3, .w = 30, .h = 10 }, .cols = 30, .rows = 15, .context_rows = 4 };
+    const layer: pardes.Layer = .{ .serial = 7, .viewport = .{ .x = 4, .y = 3, .w = 30, .h = 10 }, .cols = 30, .rows = 15, .context_rows = 4 };
     for ([_]Transition{ .slide, .zoom, .vertical }) |effect| {
         var presentation: Presentation = .{};
         const track: Track = .{ .serial = 7, .effect = effect, .frame = 4, .frame_count = 10, .from = .{ .x = 2, .y = 2, .w = 20, .h = 8 }, .to = .{ .x = 3, .y = 2, .w = 32, .h = 12 } };
@@ -699,7 +699,7 @@ test "fractional panel inverse preserves compact header rows through slide and z
             const point = presentation.pointerFractional(80, 30, x, y).?;
             try std.testing.expectApproxEqAbs(source_x, point.x, 0.0001);
             try std.testing.expectApproxEqAbs(source_y, point.y, 0.0001);
-            const body_hit = layer.hitAt(point.x * 10, point.y * 20, 10, 20, 8, 10).?;
+            const body_hit = layer.bodyHit(point.x * 10, point.y * 20, 10, 20, 8, 10).?;
             try std.testing.expectEqual(row, body_hit.row);
         }
     }
@@ -715,7 +715,7 @@ test "presentation snapshots own compact body and tag rows across later edits" {
     surface.body_layers[0] = .{ .serial = 9, .cols = 1, .rows = 2, .context_rows = 1, .cells = &body };
     var tag: [1]pardes.Cell = .{.{}};
     tag[0].text[0] = 'T';
-    surface.tag_layers[0] = .{ .kind = .pane, .serial = 9, .cols = 1, .cells = &tag };
+    surface.tag_layers[0] = .{ .kind = .pane, .serial = 9, .cols = 1, .rows = 1, .cells = &tag };
     state.capturePrevious(std.testing.allocator, &surface);
     try std.testing.expect(state.previous_valid);
     tag[0].text[0] = 'U';