018 auto discharge escaped obligation

// TEST: Auto-discharge with escaped obligation via subflow
//
// This tests the full obligation lifecycle:
// 1. get_file subflow internally calls open()
// 2. get_file returns via branch constructor - obligation ESCAPES
// 3. Main flow receives the obligation via binding 'f'
// 4. Main flow terminates with '_' - obligation unsatisfied
// 5. Auto-discharge should insert close(file: f.file) in MAIN flow
//
// Expected: Compiles successfully with auto-inserted disposal in main flow

const std = @import("std");

const File = struct { handle: i32 };

// Open a file - returns opened! state (requires cleanup)
~event open { path: []const u8 }
| opened *File[opened!]

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

// Close - the ONLY consumer of [!opened]
~event close { file: *File[!opened] }
| closed

~proc close {
    std.debug.print("Closing file (auto-discharged)\n", .{});
    return .{ .closed = .{} };
}

// Wrapper event that opens and returns file (obligation escapes)
~event get_file { path: []const u8 }
| got_file *File[opened!]

// Subflow: opens file, returns via branch constructor (obligation escapes!)
~get_file = open(path: path)
| opened f |> got_file { file: f.file }

// Main flow: calls get_file, receives escaped obligation, terminates
// Auto-discharge should insert close() HERE
~get_file(path: "test.txt")
| got_file _ |> _

pub fn main() void {}