021 void chaining codegen

// FIXED: Void event chaining now generates valid Zig sequential calls
//
// Previously: When chaining void events (work |> work |> destroy), the emitter
// generated `switch (nested_result_0) { . => || { ... } }` which was invalid:
//   1. Void types cannot be switched on
//   2. `. => ||` is invalid syntax
//
// Fix: emitSubflowContinuationsWithDepth now detects void continuations
// (empty branch name) and emits sequential calls without switch.

~import "$std/control"

const std = @import("std");

const Resource = struct { id: usize };

~event create {}
| created { r: *Resource[active!] }

~proc create {
    const r = std.heap.page_allocator.create(Resource) catch unreachable;
    r.* = Resource{ .id = 42 };
    return .{ .created = .{ .r = r } };
}

~event work { r: *Resource[active] }

~proc work {
    std.debug.print("Work\n", .{});
}

~event destroy { r: *Resource[!active] }

~proc destroy {
    std.heap.page_allocator.destroy(r);
}

~event run_one {}

~run_one = create()
| created r |>
    work(r: r.r) |> work(r: r.r) |> destroy(r: r.r)

~for(0..10)
| each _ |> run_one()
| done |> _

pub fn main() void {}