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/kv.sx

@@ -0,0 +1,86 @@
+; Phase 1 — kv facet: get/put/delete/has?/keys, get-or, update.
+
+(persist-test "absent key reads nil" (persist/kv-get (persist/open) "x") nil)
+(persist-test
+  "has? false when absent"
+  (persist/kv-has? (persist/open) "x")
+  false)
+(persist-test
+  "put then get"
+  (let
+    ((b (persist/open)))
+    (begin (persist/kv-put b "x" 7) (persist/kv-get b "x")))
+  7)
+(persist-test
+  "put returns value"
+  (let ((b (persist/open))) (persist/kv-put b "x" 9))
+  9)
+(persist-test
+  "has? true after put"
+  (let
+    ((b (persist/open)))
+    (begin (persist/kv-put b "x" 1) (persist/kv-has? b "x")))
+  true)
+(persist-test
+  "put overwrites"
+  (let
+    ((b (persist/open)))
+    (begin
+      (persist/kv-put b "x" 1)
+      (persist/kv-put b "x" 2)
+      (persist/kv-get b "x")))
+  2)
+(persist-test
+  "delete removes key"
+  (let
+    ((b (persist/open)))
+    (begin
+      (persist/kv-put b "x" 1)
+      (persist/kv-delete b "x")
+      (persist/kv-has? b "x")))
+  false)
+(persist-test
+  "delete then get is nil"
+  (let
+    ((b (persist/open)))
+    (begin
+      (persist/kv-put b "x" 1)
+      (persist/kv-delete b "x")
+      (persist/kv-get b "x")))
+  nil)
+(persist-test
+  "keys lists stored keys"
+  (let
+    ((b (persist/open)))
+    (begin
+      (persist/kv-put b "a" 1)
+      (persist/kv-put b "b" 2)
+      (len (persist/kv-keys b))))
+  2)
+(persist-test
+  "get-or returns default when absent"
+  (persist/kv-get-or (persist/open) "x" 99)
+  99)
+(persist-test
+  "get-or returns value when present"
+  (let
+    ((b (persist/open)))
+    (begin
+      (persist/kv-put b "x" 5)
+      (persist/kv-get-or b "x" 99)))
+  5)
+(persist-test
+  "kv-update applies fn over default"
+  (let
+    ((b (persist/open)))
+    (begin
+      (persist/kv-update b "n" 0 (fn (v) (+ v 1)))
+      (persist/kv-update b "n" 0 (fn (v) (+ v 1)))
+      (persist/kv-get b "n")))
+  2)
+(persist-test
+  "kv facet does not touch log"
+  (let
+    ((b (persist/open)))
+    (begin (persist/kv-put b "x" 1) (persist/count b "x")))
+  0)