060 string payload canonical

// `string` is the canonical surface type for text in an event payload.
// This is 020_016_destructure_basic with ONE word changed — `[]const u8`
// became `string` on the `name` field — and nothing else. Same behavior:
// `string` lowers to `[]const u8` for Zig, so destructure, `when`-guard,
// and `{{ name:s }}` formatting all work identically.
~import std/io

~pub event fetch { id: i64 }
| found { name: string, age: i64 }
| missing

~proc fetch|zig {
    if (id == 1) return .{ .found = .{ .name = "lars", .age = 44 } };
    return .{ .missing = .{} };
}

~fetch(id: 1)
| found { name, age: i64 } when age > 40 |> std/io:print.ln("elder {{ name:s }} {{ age:d }}")
| found { name } |> std/io:print.ln("younger {{ name:s }}")
| missing |> std/io:print.ln("nope")