008 obligation escapes via interface

const std = @import("std");
const File = struct { handle: i32 };

~pub tor open { path: string } -> *File<opened!>

~proc open|zig {
    std.debug.print("Opening file: {s}\n", .{path});
    const allocator = std.heap.page_allocator;
    const f = allocator.create(File) catch unreachable;
    f.* = File{ .handle = 42 };
    return f;
}

~pub tor close { file: *File<!opened> }

~proc close|zig {
    std.debug.print("Closing file\n", .{});
}

// Subflow that opens a file and returns it with obligation
// The obligation escapes via the return signature - caller must handle it
~pub tor my-subflow {} -> *File<opened!>

// SUBFLOW: opens a file and bare-returns it, threading the <opened!>
// obligation through the return signature to the caller.
~my-subflow = open(path: "data.txt"): f -> f