mk: phase 2C — conde, the canonical and-or sugar

conde.sx is a single defmacro: (conde (g1a g1b ...) (g2a g2b ...) ...) folds
to (mk-disj (mk-conj g1a g1b ...) (mk-conj g2a g2b ...) ...). 9 tests cover
single/multi-clause, mixed success/failure, conjunction inside clauses,
fresh+disj inside a clause, nesting, and all-fail / no-clauses.

100/100 cumulative.

plans/minikanren-on-sx.md

@@ -75,7 +75,10 @@ Key semantic mappings:
 - [x] `fresh` — introduces logic variables inside a goal body. Implemented as a
       defmacro: `(fresh (x y) g1 g2 ...)` ⇒ `(let ((x (make-var)) (y (make-var)))
       (mk-conj g1 g2 ...))`. Also `call-fresh` for programmatic goal building.
-- [ ] `conde` — sugar over disj+conj, one row per clause
+- [x] `conde` — sugar over disj+conj, one row per clause; defmacro that
+      wraps each clause body in `mk-conj` and folds via `mk-disj`. Notes:
+      with eager streams ordering is left-clause-first DFS; true interleaving
+      requires paused thunks (Phase 4 recursive relations).
 - [ ] `condu` — committed choice (soft-cut)
 - [ ] `onceo` — succeeds at most once
 - [ ] Tests: basic goal composition, backtracking, interleaving
@@ -143,6 +146,10 @@ _(none yet)_
 
 _Newest first._
 
+- **2026-05-07** — **Phase 2 piece C** (`conde`): `lib/minikanren/conde.sx` — single
+  defmacro folding clauses through `mk-disj` with internal `mk-conj`. 9 tests in
+  `tests/conde.sx`, 100/100 cumulative. Confirmed eager DFS ordering for ==-only
+  streams; true interleaving is a Phase 4 concern (paused thunks under recursion).
 - **2026-05-07** — **Phase 2 piece B** (`fresh`): `lib/minikanren/fresh.sx` (~10 lines).
   defmacro form for nice user-facing syntax + `call-fresh` for programmatic use.
   9 new tests in `tests/fresh.sx`, 91/91 cumulative.