input: crash binding can configure which thread to crash

src/renderer/Thread.zig

@@ -270,6 +270,8 @@ fn drainMailbox(self: *Thread) !void {
     while (self.mailbox.pop()) |message| {
         log.debug("mailbox message={}", .{message});
         switch (message) {
+            .crash => @panic("crash request, crashing intentionally"),
+
             .visible => |v| {
                 // Set our visible state
                 self.flags.visible = v;

src/renderer/message.zig

@@ -8,6 +8,10 @@ const terminal = @import("../terminal/main.zig");
 
 /// The messages that can be sent to a renderer thread.
 pub const Message = union(enum) {
+    /// Purposely crash the renderer. This is used for testing and debugging.
+    /// See the "crash" binding action.
+    crash: void,
+
     /// A change in state in the window focus that this renderer is
     /// rendering within. This is only sent when a change is detected so
     /// the renderer is expected to handle all of these.