persist: read-side query helpers — seq/time/type/predicate scans + 9 tests

query.sx: read-between (seq range), read-since/read-window (by :at),
read-by-type, read-where, count-where. Pure scans over persist/read for audit
windows, type filters, since-cursors. 152/152.

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

lib/persist/tests/query.sx

@@ -0,0 +1,101 @@
+; Extension — read-side query helpers. Assertions count / index, not map vs list.
+
+(define q-seqs (fn (es) (map persist/event-seq es)))
+
+(persist-test
+  "read-between slices a seq range"
+  (let
+    ((b (persist/open)))
+    (begin
+      (persist/append b "s" "x" 0 {})
+      (persist/append b "s" "x" 0 {})
+      (persist/append b "s" "x" 0 {})
+      (persist/append b "s" "x" 0 {})
+      (let
+        ((es (persist/read-between b "s" 2 3)))
+        (list
+          (len es)
+          (persist/event-seq (first es))
+          (persist/event-seq (nth es 1))))))
+  (list 2 2 3))
+(persist-test
+  "read-between is inclusive of endpoints"
+  (let
+    ((b (persist/open)))
+    (begin
+      (persist/append b "s" "x" 0 {})
+      (persist/append b "s" "x" 0 {})
+      (persist/append b "s" "x" 0 {})
+      (len (persist/read-between b "s" 1 3))))
+  3)
+(persist-test
+  "read-since filters by timestamp"
+  (let
+    ((b (persist/open)))
+    (begin
+      (persist/append b "s" "x" 100 {})
+      (persist/append b "s" "x" 200 {})
+      (persist/append b "s" "x" 300 {})
+      (len (persist/read-since b "s" 200))))
+  2)
+(persist-test
+  "read-window is an inclusive time range"
+  (let
+    ((b (persist/open)))
+    (begin
+      (persist/append b "s" "x" 100 {})
+      (persist/append b "s" "x" 200 {})
+      (persist/append b "s" "x" 300 {})
+      (persist/append b "s" "x" 400 {})
+      (len (persist/read-window b "s" 200 300))))
+  2)
+(persist-test
+  "read-by-type filters by event type"
+  (let
+    ((b (persist/open)))
+    (begin
+      (persist/append b "s" "created" 0 {})
+      (persist/append b "s" "updated" 0 {})
+      (persist/append b "s" "created" 0 {})
+      (len (persist/read-by-type b "s" "created"))))
+  2)
+(persist-test
+  "read-where filters by predicate over data"
+  (let
+    ((b (persist/open)))
+    (begin
+      (persist/append b "s" "x" 0 {:amt 5})
+      (persist/append b "s" "x" 0 {:amt 15})
+      (persist/append b "s" "x" 0 {:amt 25})
+      (len
+        (persist/read-where
+          b
+          "s"
+          (fn (e) (> (get (persist/event-data e) :amt) 10))))))
+  2)
+(persist-test
+  "count-where counts matches"
+  (let
+    ((b (persist/open)))
+    (begin
+      (persist/append b "s" "a" 0 {})
+      (persist/append b "s" "b" 0 {})
+      (persist/append b "s" "a" 0 {})
+      (persist/count-where
+        b
+        "s"
+        (fn (e) (equal? (persist/event-type e) "a")))))
+  2)
+(persist-test
+  "queries return empty on empty stream"
+  (len (persist/read-since (persist/open) "s" 0))
+  0)
+(persist-test
+  "queries work on the durable backend"
+  (let
+    ((db (persist/mock-durable (persist/mem-backend))))
+    (begin
+      (persist/append db "s" "x" 100 {})
+      (persist/append db "s" "x" 200 {})
+      (len (persist/read-since db "s" 150))))
+  1)