049 default discharge annotation

~import std/io
const std = @import("std");
const File = struct { handle: i32, dirty: bool };
~event open { path: []const u8 } -> *File<opened!>
~proc open|zig {
    const f = std.heap.page_allocator.create(File) catch unreachable;
    f.* = File{ .handle = 42, .dirty = false };
    return f;
}
~[!]event close { file: *File<!opened> }
~proc close|zig {
    std.debug.print("closed\n", .{});
    std.heap.page_allocator.destroy(file);
}
~event flush-close { file: *File<!opened> }
~proc flush-close|zig {
    std.debug.print("flushing...\n", .{});
    std.heap.page_allocator.destroy(file);
}
~open(path: "test.txt")