diff --git a/crates/wasm-actor/tests/wasm_actor.rs b/crates/wasm-actor/tests/wasm_actor.rs
index e5c0436..33112ee 100644
--- a/crates/wasm-actor/tests/wasm_actor.rs
+++ b/crates/wasm-actor/tests/wasm_actor.rs
@@ -12821,4 +12821,149 @@ fn echo_preserves_fifo_with_incrementing_bytes() {
     for (i, &b) in msgs.iter().enumerate() {
         assert_eq!(b, i as u8, "FIFO order preserved");
     }
+}
+
+// ── Cycle 89 ─────────────────────────────────────────────────────────────────
+
+// Guest computes running average (integer) over received bytes
+#[test]
+fn guest_running_sum_across_messages() {
+    let wat = r#"(module
+        (import "swactor" "send" (func $send (param i32 i32 i32)))
+        (memory (export "memory") 1)
+        (global $sum (mut i32) (i32.const 0))
+        (func (export "alloc") (param $len i32) (result i32) i32.const 1024)
+        (func (export "handle") (param $ptr i32) (param $len i32)
+            (local $i i32)
+            ;; Add all bytes to running sum
+            (local.set $i (i32.const 0))
+            (block $exit
+                (loop $loop
+                    (br_if $exit (i32.ge_u (local.get $i) (local.get $len)))
+                    (global.set $sum (i32.add (global.get $sum)
+                        (i32.load8_u (i32.add (local.get $ptr) (local.get $i)))))
+                    (local.set $i (i32.add (local.get $i) (i32.const 1)))
+                    (br $loop)
+                )
+            )
+        )
+    )"#;
+    let engine = SharedEngine::new().unwrap();
+    let actor = WasmActorBuilder::new(engine, wat::parse_str(wat).unwrap())
+        .build().unwrap();
+    let rt = Runtime::new(RuntimeConfig::default());
+    let addr = rt.spawn(actor).unwrap();
+
+    // Send 3 messages with known byte sums
+    rt.send_to(addr, ByteMessage(vec![1, 2, 3])).unwrap();        // sum += 6
+    rt.send_to(addr, ByteMessage(vec![10, 20])).unwrap();          // sum += 30
+    rt.send_to(addr, ByteMessage(vec![100])).unwrap();             // sum += 100
+    rt.tick(); // total sum = 136
+}
+
+// Build same actor type 10 times in parallel threads
+#[test]
+fn parallel_build_ten_actors() {
+    let engine = SharedEngine::new().unwrap();
+    let actors: Vec<WasmActor> = std::thread::scope(|s| {
+        let handles: Vec<_> = (0..10)
+            .map(|_| {
+                let e = engine.clone();
+                s.spawn(move || {
+                    WasmActorBuilder::new(e, guest_wasm("echo")).build().unwrap()
+                })
+            })
+            .collect();
+        handles.into_iter().map(|h| h.join().unwrap()).collect()
+    });
+
+    let rt = Runtime::new(RuntimeConfig::default());
+    let inbox = rt.new_inbox::<ByteMessage>().unwrap();
+    for actor in actors {
+        let addr = rt.spawn(actor).unwrap();
+        rt.send_to(addr, framed_msg(inbox.addr(), b"parallel")).unwrap();
+    }
+    rt.tick();
+
+    let count = std::iter::from_fn(|| inbox.try_recv()).count();
+    assert_eq!(count, 10);
+}
+
+// Guest with multiple memory.fill operations at different offsets
+#[test]
+fn guest_multiple_memory_fills() {
+    let wat = r#"(module
+        (memory (export "memory") 1)
+        (func (export "alloc") (param $len i32) (result i32) i32.const 1024)
+        (func (export "handle") (param $ptr i32) (param $len i32)
+            (memory.fill (i32.const 500) (i32.const 0xAA) (i32.const 100))
+            (memory.fill (i32.const 700) (i32.const 0xBB) (i32.const 100))
+            (memory.fill (i32.const 900) (i32.const 0xCC) (i32.const 100))
+        )
+    )"#;
+    let engine = SharedEngine::new().unwrap();
+    let actor = WasmActorBuilder::new(engine, wat::parse_str(wat).unwrap())
+        .build().unwrap();
+    let rt = Runtime::new(RuntimeConfig::default());
+    let addr = rt.spawn(actor).unwrap();
+    rt.send_to(addr, ByteMessage(vec![0])).unwrap();
+    rt.tick();
+}
+
+// Send 10000 bytes payload to echo — large transfer
+#[test]
+fn echo_ten_kb_payload() {
+    let engine = SharedEngine::new().unwrap();
+    let actor = WasmActorBuilder::new(engine, guest_wasm("echo")).build().unwrap();
+    let rt = Runtime::new(RuntimeConfig::default());
+    let inbox = rt.new_inbox::<ByteMessage>().unwrap();
+    let addr = rt.spawn(actor).unwrap();
+
+    let payload: Vec<u8> = (0..10000).map(|i| ((i * 7 + 13) % 256) as u8).collect();
+    rt.send_to(addr, framed_msg(inbox.addr(), &payload)).unwrap();
+    rt.tick();
+
+    let resp = inbox.try_recv().expect("10KB echo");
+    assert_eq!(resp.0, payload);
+}
+
+// Guest that returns negative alloc on second call — first message works, second dropped
+#[test]
+fn alloc_works_then_returns_negative() {
+    let wat = r#"(module
+        (import "swactor" "send" (func $send (param i32 i32 i32)))
+        (memory (export "memory") 1)
+        (global $call (mut i32) (i32.const 0))
+        (func (export "alloc") (param $len i32) (result i32)
+            (if (result i32) (i32.eqz (global.get $call))
+                (then
+                    (global.set $call (i32.const 1))
+                    (i32.const 1024)
+                )
+                (else (i32.const -1))
+            )
+        )
+        (func (export "handle") (param $ptr i32) (param $len i32)
+            (if (i32.ge_u (local.get $len) (i32.const 33))
+                (then (call $send (local.get $ptr)
+                    (i32.add (local.get $ptr) (i32.const 32))
+                    (i32.sub (local.get $len) (i32.const 32)))))
+        )
+    )"#;
+    let engine = SharedEngine::new().unwrap();
+    let actor = WasmActorBuilder::new(engine, wat::parse_str(wat).unwrap())
+        .build().unwrap();
+    let rt = Runtime::new(RuntimeConfig::default());
+    let inbox = rt.new_inbox::<ByteMessage>().unwrap();
+    let addr = rt.spawn(actor).unwrap();
+
+    // First: works
+    rt.send_to(addr, framed_msg(inbox.addr(), b"ok")).unwrap();
+    rt.tick();
+    assert_eq!(inbox.try_recv().unwrap().0, b"ok");
+
+    // Second: alloc returns -1, dropped
+    rt.send_to(addr, framed_msg(inbox.addr(), b"drop")).unwrap();
+    rt.tick();
+    assert!(inbox.try_recv().is_none());
 }
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