persist: Phase 1 — log + kv facets on injectable in-memory backend + 28 tests

event/backend/log/kv/api over one injected backend protocol (mem default).
log: append/read/read-from, sequential per-stream seq, stream isolation.
kv: get/put/delete/has?/keys/get-or/update. conformance.sh + 3 suites, 28/28.

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

lib/persist/tests/event.sx

@@ -0,0 +1,30 @@
+; Phase 1 — event record accessors. Uses the persist-test harness
+; (persist-test name got expected) provided by conformance.sh.
+
+(persist-test
+  "event-stream"
+  (persist/event-stream
+    (persist/event "s" 1 "t" 0 {}))
+  "s")
+(persist-test
+  "event-seq"
+  (persist/event-seq (persist/event "s" 3 "t" 0 {}))
+  3)
+(persist-test
+  "event-type"
+  (persist/event-type
+    (persist/event "s" 1 "create" 0 {}))
+  "create")
+(persist-test
+  "event-at"
+  (persist/event-at (persist/event "s" 1 "t" 42 {}))
+  42)
+(persist-test
+  "event-data"
+  (persist/event-data
+    (persist/event "s" 1 "t" 0 {:x 9}))
+  {:x 9})
+(persist-test
+  "event is a dict with all fields"
+  (len (keys (persist/event "s" 1 "t" 0 {})))
+  5)