content: snapshot cache over op-log replay (snapshot.sx) + 20 tests (338/338)

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

lib/content/scoreboard.json

@@ -7,13 +7,14 @@
     "markdown": {"pass": 20, "fail": 0},
     "validate": {"pass": 17, "fail": 0},
     "store": {"pass": 29, "fail": 0},
+    "snapshot": {"pass": 20, "fail": 0},
     "crdt": {"pass": 34, "fail": 0},
     "crdt-store": {"pass": 14, "fail": 0},
     "sync": {"pass": 14, "fail": 0},
     "md-import": {"pass": 24, "fail": 0},
     "fed": {"pass": 20, "fail": 0}
   },
-  "total_pass": 318,
+  "total_pass": 338,
   "total_fail": 0,
-  "total": 318
+  "total": 338
 }