074 effect branch single fire with terminal

// Test: single-fire effect-branch + terminal in the same program.
//
// Producer fires `ready(value)` exactly once, then returns `| done value`.
// Consumer dispatches the single effect call AND the terminal cleanly.
// Fills the "single-fire with terminal" cell of the coverage grid that
// 400_072 (multi-fire with terminal) doesn't cover.

~import std/io

~pub event init { value: usize }
! ready usize
| done usize

~proc init|zig {
    ready(value);
    return .{ .done = value };
}

~init(value: 42)
! ready v |> std/io:print.blk {
    ready {{ v:d }}
}
| done v |> std/io:print.blk {
    done {{ v:d }}
}