persist: atomic batch append — contiguous block + transactional guard + 10 tests

batch.sx: persist/append-batch commits (type at data) specs as one contiguous
block; persist/append-batch-expect checks the stream is still at expected
before writing any event, so the batch is all-or-nothing under a concurrent
writer (conflict is a value, not a partial write). 162/162.

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

lib/persist/batch.sx

@@ -0,0 +1,40 @@
+; persist/batch — commit several events to a stream as one contiguous block.
+; Each spec is (type at data). Plain append-batch always appends; the -expect
+; form is the transactional commit: it checks the stream is still at `expected`
+; before writing ANY event, so a batch is all-or-nothing under a concurrent
+; writer (conflict is a value, not a partial write). For an order + its line
+; items, an audit entry + its reason, etc. Requires: lib/persist/log.sx.
+
+; append a list of (type at data) specs as one block; returns the stored events
+; (a real cons-list, in order, with contiguous seqs)
+(define
+  persist/append-batch
+  (fn
+    (b stream specs)
+    (reverse
+      (reduce
+        (fn
+          (acc spec)
+          (cons
+            (persist/append
+              b
+              stream
+              (first spec)
+              (nth spec 1)
+              (nth spec 2))
+            acc))
+        (list)
+        specs))))
+
+; transactional batch: commit all specs only if the stream is still at expected,
+; else return a conflict and write nothing
+(define
+  persist/append-batch-expect
+  (fn
+    (b stream expected specs)
+    (let
+      ((actual (persist/last-seq b stream)))
+      (if
+        (= actual expected)
+        (persist/append-batch b stream specs)
+        {:actual actual :expected expected :conflict true}))))

lib/persist/conformance.sh

@@ -13,7 +13,7 @@ if [ ! -x "$SX_SERVER" ]; then
   exit 1
 fi
 
-SUITES=(event log kv project subscribe concurrency snapshot compaction durable blob view cas catalog query recovery)
+SUITES=(event log kv project subscribe concurrency snapshot compaction durable blob view cas catalog query batch recovery)
 
 OUT_JSON="lib/persist/scoreboard.json"
 OUT_MD="lib/persist/scoreboard.md"
@@ -40,6 +40,7 @@ run_suite() {
 (load "lib/persist/view.sx")
 (load "lib/persist/catalog.sx")
 (load "lib/persist/query.sx")
+(load "lib/persist/batch.sx")
 (load "lib/persist/subscribe.sx")
 (load "lib/persist/api.sx")
 (epoch 2)

lib/persist/scoreboard.json

@@ -14,9 +14,10 @@
     "cas": {"pass": 11, "fail": 0},
     "catalog": {"pass": 10, "fail": 0},
     "query": {"pass": 9, "fail": 0},
+    "batch": {"pass": 10, "fail": 0},
     "recovery": {"pass": 6, "fail": 0}
   },
-  "total_pass": 152,
+  "total_pass": 162,
   "total_fail": 0,
-  "total": 152
+  "total": 162
 }

lib/persist/scoreboard.md

@@ -18,5 +18,6 @@ _Generated by `lib/persist/conformance.sh`_
 | cas | 11 | 0 | 11 |
 | catalog | 10 | 0 | 10 |
 | query | 9 | 0 | 9 |
+| batch | 10 | 0 | 10 |
 | recovery | 6 | 0 | 6 |
-| **Total** | **152** | **0** | **152** |
+| **Total** | **162** | **0** | **162** |

lib/persist/tests/batch.sx

@@ -0,0 +1,122 @@
+; Extension — atomic batch append: contiguous seqs, transactional all-or-nothing.
+
+(persist-test
+  "batch assigns contiguous seqs"
+  (let
+    ((b (persist/open)))
+    (let
+      ((evs (persist/append-batch b "s" (list (list "a" 0 {}) (list "b" 0 {}) (list "c" 0 {})))))
+      (list
+        (persist/event-seq (first evs))
+        (persist/event-seq (nth evs 2)))))
+  (list 1 3))
+(persist-test
+  "batch returns events in order"
+  (let
+    ((b (persist/open)))
+    (let
+      ((evs (persist/append-batch b "s" (list (list "a" 0 {}) (list "b" 0 {})))))
+      (list
+        (persist/event-type (first evs))
+        (persist/event-type (nth evs 1)))))
+  (list "a" "b"))
+(persist-test
+  "batch grows the stream by its size"
+  (let
+    ((b (persist/open)))
+    (begin
+      (persist/append-batch
+        b
+        "s"
+        (list
+          (list "a" 0 {})
+          (list "b" 0 {})
+          (list "c" 0 {})))
+      (persist/count b "s")))
+  3)
+(persist-test
+  "batch continues an existing stream"
+  (let
+    ((b (persist/open)))
+    (begin
+      (persist/append b "s" "x" 0 {})
+      (let
+        ((evs (persist/append-batch b "s" (list (list "a" 0 {}) (list "b" 0 {})))))
+        (persist/event-seq (first evs)))))
+  2)
+(persist-test
+  "empty batch is a no-op"
+  (let
+    ((b (persist/open)))
+    (begin (persist/append-batch b "s" (list)) (persist/count b "s")))
+  0)
+(persist-test
+  "batch-expect with correct seq commits all"
+  (let
+    ((b (persist/open)))
+    (begin
+      (persist/append-batch-expect
+        b
+        "s"
+        0
+        (list
+          (list "a" 0 {})
+          (list "b" 0 {})))
+      (persist/count b "s")))
+  2)
+(persist-test
+  "batch-expect with stale seq writes nothing"
+  (let
+    ((b (persist/open)))
+    (begin
+      (persist/append b "s" "x" 0 {})
+      (persist/append-batch-expect
+        b
+        "s"
+        0
+        (list
+          (list "a" 0 {})
+          (list "b" 0 {})))
+      (persist/count b "s")))
+  1)
+(persist-test
+  "batch-expect stale returns a conflict"
+  (let
+    ((b (persist/open)))
+    (begin
+      (persist/append b "s" "x" 0 {})
+      (persist/conflict?
+        (persist/append-batch-expect
+          b
+          "s"
+          0
+          (list (list "a" 0 {}))))))
+  true)
+(persist-test
+  "batch data is preserved"
+  (let
+    ((b (persist/open)))
+    (begin
+      (persist/append-batch
+        b
+        "order"
+        (list
+          (list "placed" 0 {:id 1})
+          (list "line" 0 {:sku "x"})))
+      (get
+        (persist/event-data (nth (persist/read b "order") 1))
+        :sku)))
+  "x")
+(persist-test
+  "batch works on the durable backend"
+  (let
+    ((db (persist/mock-durable (persist/mem-backend))))
+    (begin
+      (persist/append-batch
+        db
+        "s"
+        (list
+          (list "a" 0 {})
+          (list "b" 0 {})))
+      (persist/last-seq db "s")))
+  2)