mk: laziness tests — Zzz-conde + interleaving fairness

Verifies that the Zzz-wraps-each-conde-clause + mk-mplus-suspend-on-
paused-left machinery produces fair interleaving and gives finite
prefixes from infinitely-recursive relations:

- listo-aux has no base case under run* but run 4 q ... produces
  exactly the four shortest list shapes, in order.
- mk-disj of two infinite generators (ones-gen, twos-gen) with
  run 4 q ... must include both 1-prefixed and 2-prefixed answers
  (no starvation).
- run* terminates on a goal that has a finite answer set.

3 tests, 246/246 cumulative.

plans/minikanren-on-sx.md

@@ -169,6 +169,12 @@ _(none yet)_
 
 _Newest first._
 
+- **2026-05-08** — **Laziness tests**: explicitly verifies the
+  Zzz-on-conde-clauses + mk-mplus-swap-on-paused machinery: an
+  infinitely-recursive relation truncated via `run 4 q (listo-aux q)`
+  produces exactly `(() (_.0) (_.0 _.1) (_.0 _.1 _.2))`; mixing two
+  infinite generators via `mk-disj` keeps both alive (no starvation);
+  `run*` terminates on a bounded query. 3 new tests, 246/246 cumulative.
 - **2026-05-08** — **N-queens (classic miniKanren benchmark green)**:
   `lib/minikanren/queens.sx`. Encoding cols(i) = column of queen in row i;
   `ino-each` + `all-distincto` cover row/column constraints; `safe-diag`