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/query.sx

@@ -0,0 +1,54 @@
+; persist/query — read-side helpers over a stream: slice by seq range, filter by
+; timestamp / type / predicate. Pure reads composed from persist/read, no
+; backend changes. The log is bad at ad-hoc relational queries (project into a
+; kv read model for those) but these cover the common log scans: an audit window
+; by time, a type filter, a since-cursor for incremental consumers.
+; Requires: lib/persist/log.sx.
+
+; events with seq in [from, to] inclusive
+(define
+  persist/read-between
+  (fn
+    (b stream from to)
+    (filter
+      (fn
+        (e)
+        (and (>= (persist/event-seq e) from) (<= (persist/event-seq e) to)))
+      (persist/read b stream))))
+
+; events at or after a timestamp (events carry :at; never a clock here)
+(define
+  persist/read-since
+  (fn
+    (b stream at)
+    (filter (fn (e) (>= (persist/event-at e) at)) (persist/read b stream))))
+
+; events whose :at is in [from, to] inclusive — an audit window
+(define
+  persist/read-window
+  (fn
+    (b stream from to)
+    (filter
+      (fn
+        (e)
+        (and (>= (persist/event-at e) from) (<= (persist/event-at e) to)))
+      (persist/read b stream))))
+
+; events matching a predicate (e -> truthy)
+(define
+  persist/read-where
+  (fn (b stream pred) (filter pred (persist/read b stream))))
+
+; events of a given type
+(define
+  persist/read-by-type
+  (fn
+    (b stream type)
+    (filter
+      (fn (e) (equal? (persist/event-type e) type))
+      (persist/read b stream))))
+
+; count events matching a predicate
+(define
+  persist/count-where
+  (fn (b stream pred) (len (persist/read-where b stream pred))))