artdag: Phase 7 opt-reduce bridges maude normal form back to a runnable DAG + 8 tests

artdag/opt-reduce: encode a DAG cone -> opt-term, mau/creduce against the
optimisation module, decode the normal form back to build-entries and rebuild.
Result-preserving: a 5-node blur;blur;id;bright0 chain collapses to 2 nodes and an
over(I,I) dedup 3->2, both executing identically to the original; non-optimisable
DAGs round-trip their radius faithfully (unary 1+1+1 -> 3). Completes Phase 7's
bridge-back + equivalence boxes. maude-optimize 33/33, total 191/191.

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

lib/artdag/tests/maude-optimize.sx

@@ -167,3 +167,104 @@
   "distinct pipelines stay distinct"
   (artdag/opt-same-form? "blur(src, 1)" "bright(src, 1)")
   false)
+
+; ---- bridge the normal form back to a runnable DAG (opt-reduce) ----
+; result-preserving: the maude-optimised DAG executes to the same result as the
+; original, with fewer nodes. Runner is a numeric op model (blur/bright additive in
+; radius, id pass-through, over idempotent) so the pipeline algebra holds concretely.
+
+(define
+  mo-eq-runner
+  (artdag/op-table-runner
+    {:src (fn (params inputs) 0)
+      :blur (fn (params inputs) (+ (first inputs) (get params :radius)))
+      :bright (fn (params inputs) (+ (first inputs) (* 100 (get params :radius))))
+      :id (fn (params inputs) (first inputs))
+      :over (fn (params inputs) (if (= (nth inputs 0) (nth inputs 1)) (nth inputs 0) (+ (nth inputs 0) (nth inputs 1))))}))
+
+(define
+  mo-eq-result
+  (fn (dag id) (artdag/result-of (artdag/run dag mo-eq-runner (persist/open)) id)))
+
+(define
+  mo-eq-opt-result
+  (fn
+    (dag id)
+    (let
+      ((o (artdag/opt-reduce dag id)))
+      (artdag/result-of (artdag/run o mo-eq-runner (persist/open)) (artdag/opt-last (artdag/dag-order o))))))
+
+; fixture: blur;blur chain + id + zero-radius bright (all collapse to one blur)
+(define
+  mo-chain5
+  (artdag/build
+    (list
+      (list "s" "src" (list) {})
+      (list "b1" "blur" (list "s") {:radius 1})
+      (list "b2" "blur" (list "b1") {:radius 1})
+      (list "i" "id" (list "b2") {})
+      (list "z" "bright" (list "i") {:radius 0}))))
+(define mo-chain5-id (artdag/dag-id mo-chain5 "z"))
+(define mo-chain5-opt (artdag/opt-reduce mo-chain5 mo-chain5-id))
+(define mo-chain5-sink (artdag/opt-last (artdag/dag-order mo-chain5-opt)))
+
+(artdag-test
+  "opt-reduce: 5-node chain collapses to 2 nodes"
+  (artdag/node-count mo-chain5-opt)
+  2)
+
+(artdag-test
+  "opt-reduce: fused sink op is blur"
+  (artdag/node-op (artdag/dag-get mo-chain5-opt mo-chain5-sink))
+  "blur")
+
+(artdag-test
+  "opt-reduce: fused sink radius is the sum"
+  (artdag/node-params (artdag/dag-get mo-chain5-opt mo-chain5-sink))
+  {:radius 2})
+
+(artdag-test
+  "opt-reduce: result-preserving on chain"
+  (= (mo-eq-result mo-chain5 mo-chain5-id) (mo-eq-opt-result mo-chain5 mo-chain5-id))
+  true)
+
+; fixture: over of identical subpipelines (idempotent dedup)
+(define
+  mo-dedup
+  (artdag/build
+    (list
+      (list "s" "src" (list) {})
+      (list "b" "blur" (list "s") {:radius 2})
+      (list "o" "over" (list "b" "b") {} true))))
+(define mo-dedup-id (artdag/dag-id mo-dedup "o"))
+
+(artdag-test
+  "opt-reduce: over dedup collapses to 2 nodes"
+  (artdag/node-count (artdag/opt-reduce mo-dedup mo-dedup-id))
+  2)
+
+(artdag-test
+  "opt-reduce: result-preserving on dedup"
+  (= (mo-eq-result mo-dedup mo-dedup-id) (mo-eq-opt-result mo-dedup mo-dedup-id))
+  true)
+
+; non-optimisable DAG: opt-reduce is a faithful round-trip (no laws fire)
+(define
+  mo-plain
+  (artdag/build
+    (list
+      (list "s" "src" (list) {})
+      (list "b" "blur" (list "s") {:radius 3}))))
+(define mo-plain-id (artdag/dag-id mo-plain "b"))
+(define mo-plain-opt (artdag/opt-reduce mo-plain mo-plain-id))
+
+(artdag-test
+  "opt-reduce: untouched DAG keeps its node count"
+  (artdag/node-count mo-plain-opt)
+  2)
+
+(artdag-test
+  "opt-reduce: untouched DAG keeps its radius (unary round-trip)"
+  (artdag/node-params
+    (artdag/dag-get mo-plain-opt (artdag/opt-last (artdag/dag-order mo-plain-opt))))
+  {:radius 3})