mk: phase 1 — unify.sx + 48 tests, kit-driven

lib/minikanren/unify.sx wraps lib/guest/match.sx with a miniKanren-flavoured
cfg: native SX lists as cons-pairs, occurs-check off by default. ~22 lines
of local logic over kit's walk-with / unify-with / extend / occurs-with.

48 tests in lib/minikanren/tests/unify.sx exercise: var fresh-distinct,
walk chains, walk* deep into nested lists, atom/var/list unification with
positional matching, failure modes, opt-in occurs check.

plans/minikanren-on-sx.md

@@ -50,15 +50,15 @@ Key semantic mappings:
 ## Roadmap
 
 ### Phase 1 — variables + unification
-- [ ] `make-var` → fresh logic variable (unique mutable box)
-- [ ] `var?` `v` → bool — is this a logic variable?
-- [ ] `walk` `term` `subst` → follow substitution chain to ground term or unbound var
-- [ ] `walk*` `term` `subst` → deep walk (recurse into lists/dicts)
-- [ ] `unify` `u` `v` `subst` → extended substitution or `#f` (failure)
+- [x] `make-var` → fresh logic variable (unique mutable box)
+- [x] `var?` `v` → bool — is this a logic variable?
+- [x] `walk` `term` `subst` → follow substitution chain to ground term or unbound var
+- [x] `walk*` `term` `subst` → deep walk (recurse into lists/dicts)
+- [x] `unify` `u` `v` `subst` → extended substitution or `#f` (failure)
       Handles: var/var, var/term, term/var, list unification, number/string/symbol equality.
       No occurs check by default; `unify-check` with occurs check as opt-in.
-- [ ] Empty substitution `empty-s` = `(list)` (empty assoc list)
-- [ ] Tests in `lib/minikanren/tests/unify.sx`: ground terms, vars, lists, failure, occurs
+- [x] Empty substitution `empty-s` (dict-based via kit's `empty-subst` — assoc list was a sketch; kit ships dict, kept it)
+- [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)`),
@@ -135,4 +135,12 @@ _(none yet)_
 
 _Newest first._
 
-_(awaiting phase 1)_
+- **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`
+  all supplied by `lib/guest/match.sx`. Local additions: a miniKanren-flavoured cfg
+  (treats native SX lists as cons-pairs via `:ctor-head = :pair`, occurs-check off),
+  `make-var` fresh-counter, deep `mk-walk*` (kit's `walk*` only recurses into `:ctor`
+  form, not native lists), and `mk-unify` / `mk-unify-check` thin wrappers. The kit
+  earns its keep ~3× over by line count — confirms lib-guest match kit is reusable
+  for logic-language hosts as designed.