Switch over to the IO thread. A messy commit!

src/termio/Thread.zig

@@ -162,7 +162,8 @@ fn drainMailbox(self: *Thread) !void {
             log.debug("mailbox message={}", .{message});
             switch (message) {
                 .resize => |v| try self.impl.resize(v.grid_size, v.screen_size),
-                .small_write => |v| try self.impl.queueWrite(v.data[0..v.len]),
+                .write_small => |v| try self.impl.queueWrite(v.data[0..v.len]),
+                .write_stable => |v| try self.impl.queueWrite(v),
             }
         }
     }

src/termio/message.zig

@@ -1,11 +1,10 @@
 const std = @import("std");
+const Allocator = std.mem.Allocator;
 const renderer = @import("../renderer.zig");
 const terminal = @import("../terminal/main.zig");
 
 /// The messages that can be sent to an IO thread.
 pub const IO = union(enum) {
-    pub const SmallWriteArray = [22]u8;
-
     /// Resize the window.
     resize: struct {
         grid_size: renderer.GridSize,
@@ -13,10 +12,35 @@ pub const IO = union(enum) {
     },
 
     /// Write where the data fits in the union.
-    small_write: struct {
-        data: [22]u8,
+    write_small: WriteReq.Small,
+
+    /// Write where the data pointer is stable.
+    write_stable: []const u8,
+};
+
+/// Represents a write request.
+pub const WriteReq = union(enum) {
+    pub const Small = struct {
+        pub const Array = [22]u8;
+        data: Array,
         len: u8,
-    },
+    };
+
+    pub const Alloc = struct {
+        alloc: Allocator,
+        data: []u8,
+    };
+
+    /// A small write where the data fits into this union size.
+    small: Small,
+
+    /// A stable pointer so we can just pass the slice directly through.
+    /// This is useful i.e. for const data.
+    stable: []const u8,
+
+    /// Allocated and must be freed with the provided allocator. This
+    /// should be rarely used.
+    alloc: Alloc,
 };
 
 test {