maude: Phase 7 reflection / META-LEVEL (18 tests, 196 total)

lib/maude/meta.sx — up-term/down-term encode terms as data (mt-var/mt-app),
reflective meta-reduce/meta-rewrite/meta-apply, the meta-circular law
down(metaReduce(up t)) =AC= reduce t, and meta-prove-equal? as a generic
equational theorem helper. Verified round-trips, reflection agreement,
single-rule meta-apply, and proving commutativity/associativity instances.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

plans/maude-on-sx.md

@@ -97,9 +97,9 @@ The novel substrate stress: equational matching. Pattern `X + Y` against `1 + 2
 - [x] Tests: programs whose meaning depends on strategy choice.
 
 ### Phase 7 — Reflection (META-LEVEL)
-- [ ] Terms-as-data: `META-LEVEL` lets you encode/decode terms as Maude terms.
-- [ ] Build proofs / programs that manipulate Maude programs.
-- [ ] Tests: meta-circular interpretation, generic theorem helpers.
+- [x] Terms-as-data: `META-LEVEL` lets you encode/decode terms as Maude terms.
+- [x] Build proofs / programs that manipulate Maude programs.
+- [x] Tests: meta-circular interpretation, generic theorem helpers.
 
 ### Phase 8 — Propose `lib/guest/rewriting/`
 - [ ] Extract equational matching engine (the most reusable piece).
@@ -235,5 +235,19 @@ The novel substrate stress: equational matching. Pattern `X + Y` against `1 + 2
     env by binding `(define env {})` then `(dict-set! env ...)`, pass `env`.
     `srun-canon` sorts results so expected lists must be sorted.
 
+- **Phase 7 (reflection / META-LEVEL) — DONE, 196/196 total.**
+  `lib/maude/meta.sx`. `mau/up-term` re-encodes an object term as a term built
+  from meta-constructors `mt-var`(name,sort) / `mt-app`(op, args...) — a
+  represented term is itself a first-class object term you can build, inspect,
+  transform. `mau/down-term` reverses (round-trips). Reflective ops:
+  `mau/meta-reduce` / `mau/meta-rewrite` / `mau/meta-apply LABEL` take and
+  return represented terms. `mau/meta-circular?` verifies the law
+  `down(metaReduce(up t)) =AC= reduce t` (reflection agrees with the object
+  level). `mau/meta-prove-equal?` is a generic equational theorem helper
+  (prove an identity by joint reduction). Verified: up/down round-trip,
+  meta-reduce returns a represented normal form, meta-circular law on Peano,
+  meta-apply of a single rule, commutativity/associativity instance proofs,
+  and building a program at the meta level then running it.
+
 ## Blockers
 _(none)_