050 subflow field shorthand

// BUG: Subflow field shorthand { e } incorrectly emits `.{ .branch = e }` instead of `.{ .branch = .{ .e = e } }`
//
// SYNTAX DESIGN ISSUE:
// - Original: `{ e }` is shorthand for `{ e: e }` (field shorthand)
// - Later added: `branch { value }` to mean "branch with simple value"
// - These clash!
//
// PROPOSED FIX:
// - No braces = simple value:  |> result 10
// - Braces = struct:           |> entity { e }  means { e: e }
//
// CURRENT BEHAVIOR:
// - `~foo = bar { e }` emits: return .{ .bar = e };
// - SHOULD emit:              return .{ .bar = .{ .e = e } };
//
// WORKAROUND: Use explicit `{ e: e }` syntax

~import "$std/io"
~import "$std/control"

const std = @import("std");

const Entity = struct {
    id: u32,
};

~pub event test_event { e: Entity }
| result { e: Entity }

// BUG: This emits wrong code
// ~test_event = result { e }

// WORKAROUND: Explicit syntax works
~test_event = result { e: e }

~event print_result { e: Entity }
~proc print_result {
    std.debug.print("Got entity {d}\n", .{ e.id });
}

const entity = Entity{ .id = 42 };

~test_event(e: entity)
| result r |> print_result(e: r.e)