008 obligation escapes via interface

// JavaScript implementation facet of module `fs`.
// Events and types are declared in fs.kz (merged at import); this file holds
// the |js proc bodies. What the fixture pins is the obligation lifecycle, so
// the Zig facet's page_allocator.create/destroy is modelled by a plain object
// and a no-op release.

~proc open|js {
    console.log(`Opening file: ${path}`);
    return { handle: 42 };
}

~proc close|js {
    console.log("Closing file");
}

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