mk: phase 2A — streams + ==/conj/disj, 34 new tests

lib/minikanren/stream.sx: mzero/unit/mk-mplus/mk-bind/stream-take. Three
stream shapes (empty, mature list, immature thunk). mk-mplus suspends and
swaps on a paused-left for fair interleaving (Reasoned Schemer style).

lib/minikanren/goals.sx: succeed/fail/==/==-check + conj2/disj2 +
variadic mk-conj/mk-disj. ==-check is the opt-in occurs-checked variant.

Forced-rename note: SX has a host primitive `bind` that silently shadows
user-level defines, so all stream/goal operators are mk-prefixed. Recorded
in feedback memory.

82/82 tests cumulative (48 unify + 34 goals).

plans/minikanren-on-sx.md

@@ -61,14 +61,20 @@ Key semantic mappings:
 - [x] Tests in `lib/minikanren/tests/unify.sx`: ground terms, vars, lists, failure, occurs
 
 ### Phase 2 — streams + goals
-- [ ] Stream type: `mzero` (empty stream = `nil`), `unit s` (singleton = `(list s)`),
-      `mplus` (interleave two streams), `bind` (apply goal to stream)
-- [ ] Lazy streams via `delay`/`force` — mature pairs for depth-first, immature for lazy
-- [ ] `==` goal: `(fn (s) (let ((s2 (unify u v s))) (if s2 (unit s2) mzero)))`
-- [ ] `succeed` / `fail` — trivial goals
-- [ ] `fresh` — `(fn (f) (fn (s) ((f (make-var)) s)))` — introduces one var; `fresh*` for many
-- [ ] `conde` — interleaving disjunction of goal lists
-- [ ] `condu` — committed choice (soft-cut): only explores first successful clause
+- [x] Stream type: `mzero` (empty), `unit s` (singleton), `mk-mplus` (interleave),
+      `mk-bind` (apply goal to stream). Names mk-prefixed because SX has a host
+      `bind` primitive that silently shadows user defines.
+- [x] Lazy streams via thunks: a paused stream is a zero-arg fn; mk-mplus suspends
+      and swaps when its left operand is paused, giving fair interleaving.
+- [x] `==` goal: `(fn (s) (let ((s2 (mk-unify u v s))) (if s2 (unit s2) mzero)))`
+- [x] `==-check` — opt-in occurs-checked equality goal
+- [x] `succeed` / `fail` — trivial goals
+- [x] `conj2` / `mk-conj` (variadic) — sequential conjunction
+- [x] `disj2` / `mk-disj` (variadic) — interleaved disjunction (raw — `conde`
+      adds the implicit-conj-per-clause sugar later)
+- [ ] `fresh` — introduces logic variables inside a goal body
+- [ ] `conde` — sugar over disj+conj, one row per clause
+- [ ] `condu` — committed choice (soft-cut)
 - [ ] `onceo` — succeeds at most once
 - [ ] Tests: basic goal composition, backtracking, interleaving
 
@@ -135,6 +141,12 @@ _(none yet)_
 
 _Newest first._
 
+- **2026-05-07** — **Phase 2 piece A** (streams + ==/conj/disj): `lib/minikanren/stream.sx`
+  (mzero/unit/mk-mplus/mk-bind/stream-take, ~25 lines of code) + `lib/minikanren/goals.sx`
+  (succeed/fail/==/==-check/conj2/disj2/mk-conj/mk-disj, ~30 lines). Found and noted
+  a host-primitive name clash: `bind` is built in and silently shadows user defines —
+  must use `mk-bind`/`mk-mplus` etc. throughout. 34 tests in `tests/goals.sx`,
+  82/82 cumulative all green. fresh/conde/condu/onceo still pending.
 - **2026-05-07** — **Phase 1 done**: `lib/minikanren/unify.sx` (53 lines, ~22 lines of actual code) +
   `lib/minikanren/tests/unify.sx` (48 tests, all green). Kit consumption: `walk-with`,
   `unify-with`, `occurs-with`, `extend`, `empty-subst`, `mk-var`, `is-var?`, `var-name`