artdag: DAG wire serialization — portable record form + integrity + 13 tests

serialize.sx emits a topo-ordered (id op inputs params commutative) record list
that survives write/read (string-keyed node dicts do not; empty inputs read back
as nil and are normalized). wire->dag reconstructs a runnable dag by content-id;
wire-verify recomputes ids to reject tampering. dag->string/string->dag for text
transport. serialize 13/13, total 128/128.

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

plans/artdag-on-sx.md

@@ -30,7 +30,7 @@ edges.
 
 ## Status (rolling)
 
-`bash lib/artdag/conformance.sh` → **115/115** (7 suites: dag, analyze, plan, execute, optimize, fed, cost)
+`bash lib/artdag/conformance.sh` → **128/128** (8 suites: dag, analyze, plan, execute, optimize, fed, cost, serialize)
 
 Base roadmap (Phases 1–6) COMPLETE. Now extending.
 
@@ -138,6 +138,17 @@ lib/artdag/optimize.sx                  lib/artdag/federation.sx
 
 ## Progress log
 
+- **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
+  dicts, which survive `write-to-string`/`read` (string-keyed node dicts do NOT; and
+  `()` reads back as nil, so `wire->dag` normalizes empty inputs). `wire->dag`
+  reconstructs a runnable dag by content-id (author names dropped); executes
+  identically to the original. `wire-verify` recomputes each record's content-id and
+  rejects tampered ids or mutated params under a stale id (self-verifying transport).
+  `dag->string`/`string->dag` for text transport. Gotcha logged: `sx-parse` primitive
+  is unbound in the server env — use `(read (open-input-string s))`.
+
 - **Ext: cost-based scheduling** (cost suite 13/13, total 115/115).
   `lib/artdag/cost.sx`: an injected `cost-fn (op params)` keeps media-op costs opaque
   (`const-cost`, `op-cost table`). `critical-path` = longest weighted path (finish-time