phantom state valid

// Test 910: Phantom State Valid Transitions
//
// Validates that phantom state transitions work correctly when states match.
//
// This test shows the happy path:
// - open_file returns *File[open]
// - close_file accepts *File[open] and returns *File[closed]
// - States match, compilation succeeds!

const std = @import("std");

~event open_file {}
| opened { file: *std.fs.File[open] }

~proc open_file {
    std.debug.print("File opened\n", .{});
    const allocator = std.heap.page_allocator;
    const f = allocator.create(std.fs.File) catch unreachable;
    return .{ .opened = .{ .file = f } };
}

~event close_file { file: *std.fs.File[open] }
| closed { file: *std.fs.File[closed] }

~proc close_file {
    std.debug.print("File closed\n", .{});
    return .{ .closed = .{ .file = file } };
}

// This flow should SUCCEED: [open] → close_file accepts [open] → returns [closed]
~open_file()
| opened o |> close_file(file: o.file)
    | closed _ |> _