maude: artdag-on-sx fit prototype — optimise passes as equations (8 tests, 262 total)

lib/maude/tests/effects.sx — proves artdag's effect-pipeline optimisations
(fusion, no-op/dead-op elim, identity elim, CSE/idempotent dedup) are
equational rewriting: the optimised pipeline is the normal form, confluence
gives a stable content id. The 'second consumer' spike for a maude-driven
optimiser in lib/artdag. Surfaced faithfulness note: id: affects matching/canon
not auto-reduction.

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

plans/maude-on-sx.md

@@ -153,7 +153,16 @@ sorts/subsorts/overloading, equational reduction modulo assoc/comm/id,
 conditional eqs + owise, system rules (rew + BFS search with witness paths),
 a strategy language, and META-LEVEL reflection, with a mixfix surface printer
 and an end-to-end `.maude` runner (reduce/rewrite/search commands, sort-annotated
-output). Pacing down to hardening. Possible niche future work: membership
+output). **artdag-on-sx fit prototype (lib/maude/tests/effects.sx, 8 tests):** artdag's
+optimise passes — adjacent-op fusion, no-op/dead-op elim, identity elim,
+CSE/idempotent dedup — expressed as `eq`s; the optimised pipeline IS the normal
+form, and confluence ⇒ a stable content id. This is the "second consumer"
+spike: it justifies a maude-driven optimiser in `lib/artdag` and the eventual
+`lib/guest/rewriting/` extraction. Faithfulness note surfaced: `id:` only
+affects matching/canon, NOT auto-reduction — write explicit identity eqs (or
+read off the canonical form) if you need `0 + N` to reduce in the term itself.
+
+Pacing down to hardening. Possible niche future work: membership
 axioms (`mb`/`cmb`), critical-pair / confluence checking, meta-search, full
 mixfix (multi-`_` ops, juxtaposition `__`).