artdag: Phase 7 optimisation laws as confluent maude module + 11 tests

lib/artdag/optimize-rules.sx — the effect-pipeline optimisation passes (identity
elim, no-op/zero-radius elim, adjacent fusion, idempotent over dedup) as a maude
module. Radius algebra is _+_ [assoc comm id: 0] (NOT Peano successor rules, which
are non-confluent here); mau/confluent? certifies 0 non-joinable critical pairs, so
the optimised pipeline's normal form / content id is rewrite-order stable. Consumes
lib/maude/confluence.sx. maude-optimize 25/25, total 183/183.

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

lib/artdag/tests/maude-optimize.sx

@@ -110,3 +110,60 @@
     (artdag/dag-id mo-diamond "a")
     (keys (artdag/dag-nodes mo-diamond-rt)))
   true)
+
+; ---- optimisation laws as a confluent maude module (optimize-rules.sx) ----
+; The optimised pipeline is the normal form; confluence => stable content id.
+
+(artdag-test "opt module is confluent" (artdag/opt-confluent?) true)
+
+(artdag-test
+  "opt module has no non-joinable critical pairs"
+  (len (artdag/opt-non-joinable))
+  0)
+
+(artdag-test
+  "law: identity elimination"
+  (artdag/opt-normal-form "id(src)")
+  "src")
+
+(artdag-test
+  "law: zero-radius blur is a no-op"
+  (artdag/opt-normal-form "blur(src, 0)")
+  "src")
+
+(artdag-test
+  "law: zero-radius bright is a no-op"
+  (artdag/opt-normal-form "bright(src, 0)")
+  "src")
+
+(artdag-test
+  "law: adjacent blur fusion adds radii"
+  (artdag/opt-normal-form "blur(blur(src, 1), 1)")
+  "blur(src, _+_(1, 1))")
+
+(artdag-test
+  "fusion normal form is rewrite-order stable"
+  (artdag/opt-same-form?
+    "blur(blur(blur(src, 1), 1), 1)"
+    "blur(blur(src, 1 + 1), 1)")
+  true)
+
+(artdag-test
+  "laws compose: id + no-op + fusion"
+  (artdag/opt-normal-form "bright(id(blur(blur(src, 1), 1)), 0)")
+  "blur(src, _+_(1, 1))")
+
+(artdag-test
+  "law: idempotent over dedup (CSE)"
+  (artdag/opt-normal-form "over(blur(src, 1), blur(src, 1))")
+  "blur(src, 1)")
+
+(artdag-test
+  "distinct over operands do not dedup"
+  (artdag/opt-same-form? "over(blur(src, 1), blur(src, 1 + 1))" "blur(src, 1)")
+  false)
+
+(artdag-test
+  "distinct pipelines stay distinct"
+  (artdag/opt-same-form? "blur(src, 1)" "bright(src, 1)")
+  false)