072 effect branch multifire with terminal

// Test: multi-fire effect-branch pump WITH terminal — the canonical iterator shape.
//
// `count-up(start: 0, end: 3)` yields three `! each` operations (i = 0, 1, 2),
// then returns `| done 3`. Consumer handles each yield by printing the index,
// and handles the terminal by printing the total count. This is the smallest
// program that exercises BOTH branch kinds together at runtime: yielding conts
// lower into the synthesized Handlers struct, terminal conts drive the
// post-call switch/extract. Proves partition logic doesn't drop either path.

~import std/io

~pub event count-up { start: usize, end: usize }
! each usize
| done usize

~proc count-up|zig {
    for (start..end) |i| {
        each(i);
    }
    return .{ .done = end };
}

~count-up(start: 0, end: 3)
! each i |> std/io:print.blk {
    each {{ i:d }}
}
| done total |> std/io:print.blk {
    done {{ total:d }}
}