mem engine streams — coverage reconciliation against the seam task's foundation with the two unpinned engine-side pins (mem-engine-streams): the read_from_consumer cursor-read surface (absent-consumer head read, checkpoint-forward resume, tail-empty, extent clamps, name validation) and the ADR-015 trim property (saved sub-horizon checkpoints untouched — offsets never renumbered; consumer reads resume at the horizon's first remaining row). No production code changed; tests only (+2, mem suite at 99). Task file: status completed, Notes/Summary filled

alkstore-mem/src/stream.rs

@@ -644,6 +644,72 @@ mod tests {
         let _ = _a;
     }
 
+    #[tokio::test(flavor = "current_thread")]
+    async fn read_from_consumer_reads_the_cursor_and_clamps_the_extent() {
+        let store = MemStore::new();
+        let handle = handle(&store, "orders");
+        let a = handle.publish(serde_json::json!(1)).await.unwrap();
+        let b = handle.publish(serde_json::json!(2)).await.unwrap();
+        let c = handle.publish(serde_json::json!(3)).await.unwrap();
+        let head = handle.read_from_consumer("c1", 10).await.unwrap();
+        assert_eq!(
+            head.iter().map(|e| e.offset).collect::<Vec<_>>(),
+            vec![a, b, c],
+            "an absent consumer reads from the head (checkpoint 0)"
+        );
+        handle.save_offset("c1", b).await.unwrap();
+        let cursor = handle.read_from_consumer("c1", 10).await.unwrap();
+        assert_eq!(
+            cursor.iter().map(|e| e.offset).collect::<Vec<_>>(),
+            vec![c],
+            "the cursor read resumes at the saved checkpoint's forward tail"
+        );
+        assert!(handle.read_from_consumer("c1", 0).await.unwrap().is_empty());
+        assert!(
+            handle
+                .read_from_consumer("c1", -2)
+                .await
+                .unwrap()
+                .is_empty(),
+            "the extent guard clamps non-positive limits to empty"
+        );
+        handle.save_offset("c1", c).await.unwrap();
+        assert!(
+            handle
+                .read_from_consumer("c1", 10)
+                .await
+                .unwrap()
+                .is_empty(),
+            "a cursor at the tail reads empty"
+        );
+        match handle.read_from_consumer("", 10).await {
+            Err(alkstore::Error::InvalidName { .. }) => {}
+            _other => panic!("an empty consumer name rejects"),
+        }
+    }
+
+    #[tokio::test(flavor = "current_thread")]
+    async fn saved_sub_horizon_offsets_survive_trim_and_consumer_reads_resume_at_the_horizon() {
+        let store = MemStore::new();
+        let handle = handle(&store, "orders");
+        let a = handle.publish(serde_json::json!(1)).await.unwrap();
+        let b = handle.publish(serde_json::json!(2)).await.unwrap();
+        let _c = handle.publish(serde_json::json!(3)).await.unwrap();
+        handle.save_offset("c1", a).await.unwrap();
+        assert_eq!(handle.trim_to(b - 1).await.unwrap(), 1);
+        assert_eq!(
+            handle.get_offset("c1").await.unwrap(),
+            a,
+            "the saved sub-horizon checkpoint is untouched by trim — offsets are never renumbered"
+        );
+        let resumed = handle.read_from_consumer("c1", 10).await.unwrap();
+        assert_eq!(
+            resumed.iter().map(|e| e.offset).collect::<Vec<_>>(),
+            vec![b, _c],
+            "reads from a trimmed-away region resume at the horizon's first remaining row"
+        );
+    }
+
     #[tokio::test(flavor = "current_thread")]
     async fn receiver_try_recv_reads_without_await() {
         let store = MemStore::new();