artdag: optimize composition pass (fuse + dce) + 4 tests

artdag/optimize entries outputs fusible? fuses the entry list then DCEs against
the output names — sinks survive fusion (never absorbed), so output-equivalent
with fewer nodes. optimize 22/22, total 132/132.

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

lib/artdag/optimize.sx

@@ -4,6 +4,7 @@
 ;            already collapse to one node at build time (artdag/cse == build).
 ;   Fusion — collapse a maximal 1-to-1 chain of fusible unary ops into a single
 ;            "artdag/pipeline" node that replays the stages; output-equivalent.
+;   optimize — fuse then DCE in one pass.
 ; Depends on dag.sx and analyze.sx.
 
 ; ---- dict helper ----
@@ -188,3 +189,14 @@
         (= op artdag/pipeline-op)
         ((artdag/pipeline-run base-runner) params inputs)
         (base-runner op params inputs)))))
+
+; ---- full optimization pass ----
+; fuse the entry list, then drop everything not feeding the requested output
+; names. Output names survive fusion (sinks are never absorbed).
+(define
+  artdag/optimize
+  (fn
+    (entries outputs fusible?)
+    (let
+      ((fused (artdag/fuse entries fusible?)))
+      (artdag/dce fused (map (fn (nm) (artdag/dag-id fused nm)) outputs)))))

lib/artdag/scoreboard.json

@@ -4,12 +4,12 @@
     "analyze": {"pass": 16, "fail": 0},
     "plan": {"pass": 18, "fail": 0},
     "execute": {"pass": 15, "fail": 0},
-    "optimize": {"pass": 18, "fail": 0},
+    "optimize": {"pass": 22, "fail": 0},
     "fed": {"pass": 15, "fail": 0},
     "cost": {"pass": 13, "fail": 0},
     "serialize": {"pass": 13, "fail": 0}
   },
-  "total_pass": 128,
+  "total_pass": 132,
   "total_fail": 0,
-  "total": 128
+  "total": 132
 }

lib/artdag/scoreboard.md

@@ -8,8 +8,8 @@ _Generated by `lib/artdag/conformance.sh`_
 | analyze | 16 | 0 | 16 |
 | plan | 18 | 0 | 18 |
 | execute | 15 | 0 | 15 |
-| optimize | 18 | 0 | 18 |
+| optimize | 22 | 0 | 22 |
 | fed | 15 | 0 | 15 |
 | cost | 13 | 0 | 13 |
 | serialize | 13 | 0 | 13 |
-| **Total** | **128** | **0** | **128** |
+| **Total** | **132** | **0** | **132** |

lib/artdag/tests/optimize.sx

@@ -174,3 +174,42 @@
   "fusion: empty fusible set leaves dag unchanged"
   (artdag/node-count (artdag/fuse opt-chain (fn (op) false)))
   4)
+
+; ---- full optimization pass (fuse + dce) ----
+
+(define
+  optp-entries
+  (list
+    (list "a" "in" (list) {:v 5})
+    (list "b" "inc" (list "a") {})
+    (list "c" "inc" (list "b") {})
+    (list "x" "sq" (list "a") {})))
+
+(artdag-test
+  "optimize: fuses chain and drops dead node"
+  (artdag/node-count (artdag/optimize optp-entries (list "c") opt-inc?))
+  2)
+
+(artdag-test
+  "optimize: leaves dead node when it is an output"
+  (artdag/node-count (artdag/optimize optp-entries (list "c" "x") opt-inc?))
+  3)
+
+(artdag-test
+  "optimize: result equals the unoptimized dag"
+  (let
+    ((c1 (persist/open)) (c2 (persist/open)))
+    (let
+      ((o (artdag/optimize optp-entries (list "c") opt-inc?)))
+      (=
+        (artdag/result-of (artdag/run o opt-RUN c1) (artdag/dag-id o "c"))
+        (artdag/result-of
+          (artdag/run (artdag/build optp-entries) opt-RUN c2)
+          (artdag/dag-id (artdag/build optp-entries) "c")))))
+  true)
+
+(artdag-test
+  "optimize: no fusible ops still drops dead nodes"
+  (artdag/node-count
+    (artdag/optimize optp-entries (list "c") (fn (op) false)))
+  3)

plans/artdag-on-sx.md

@@ -30,7 +30,7 @@ edges.
 
 ## Status (rolling)
 
-`bash lib/artdag/conformance.sh` → **128/128** (8 suites: dag, analyze, plan, execute, optimize, fed, cost, serialize)
+`bash lib/artdag/conformance.sh` → **132/132** (8 suites: dag, analyze, plan, execute, optimize, fed, cost, serialize)
 
 Base roadmap (Phases 1–6) COMPLETE. Now extending.
 
@@ -138,6 +138,12 @@ lib/artdag/optimize.sx                  lib/artdag/federation.sx
 
 ## Progress log
 
+- **Ext: optimize composition pass** (optimize suite 22/22, total 132/132).
+  `artdag/optimize entries outputs fusible?` fuses the entry list then DCEs against
+  the output names (sinks survive fusion since they're never absorbed) — fewer nodes,
+  identical results. Verified: dead branch dropped + chain fused (4→2), an output that
+  is itself "dead" is retained, no-fusible-set still DCEs.
+
 - **Ext: DAG wire serialization** (serialize suite 13/13, total 128/128).
   `lib/artdag/serialize.sx`: `dag->wire` emits a topo-ordered list of
   `(id op inputs params commutative)` records — plain lists with keyword-keyed param