diff --git a/crates/wasm-actor/tests/wasm_actor.rs b/crates/wasm-actor/tests/wasm_actor.rs
index 1c6a13f..afd6868 100644
--- a/crates/wasm-actor/tests/wasm_actor.rs
+++ b/crates/wasm-actor/tests/wasm_actor.rs
@@ -9622,4 +9622,137 @@ fn two_actors_from_cloned_wasm_bytes() {
 
     assert_eq!(inbox1.try_recv().unwrap().0, b"one");
     assert_eq!(inbox2.try_recv().unwrap().0, b"two");
+}
+
+// ── Cycle 66 ─────────────────────────────────────────────────────────────────
+
+// Guest uses i32.shr_u (logical right shift)
+#[test]
+fn guest_uses_logical_right_shift() {
+    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)
+            ;; Load 4 bytes from ptr, shift right by 4, store back
+            (i32.store (local.get $ptr)
+                (i32.shr_u (i32.load (local.get $ptr)) (i32.const 4))
+            )
+        )
+    )"#;
+    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![0xFF, 0x00, 0x00, 0x00])).unwrap();
+    rt.tick();
+}
+
+// Long-lived actor: 100 messages across 100 ticks
+#[test]
+fn hundred_messages_across_hundred_ticks() {
+    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();
+
+    for i in 0u8..100 {
+        rt.send_to(addr, framed_msg(inbox.addr(), &[i])).unwrap();
+        rt.tick();
+        let resp = inbox.try_recv().expect("each tick should echo");
+        assert_eq!(resp.0, vec![i], "tick {i} content mismatch");
+    }
+}
+
+// Guest with nested if/else chains
+#[test]
+fn guest_nested_if_else_three_deep() {
+    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)
+            (if (i32.gt_u (local.get $len) (i32.const 10))
+                (then
+                    (if (i32.gt_u (local.get $len) (i32.const 20))
+                        (then
+                            (if (i32.gt_u (local.get $len) (i32.const 30))
+                                (then (i32.store (local.get $ptr) (i32.const 3)))
+                                (else (i32.store (local.get $ptr) (i32.const 2)))
+                            )
+                        )
+                        (else (i32.store (local.get $ptr) (i32.const 1)))
+                    )
+                )
+                (else (i32.store (local.get $ptr) (i32.const 0)))
+            )
+        )
+    )"#;
+    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();
+
+    // len=5 → branch 0, len=15 → branch 1, len=25 → branch 2, len=35 → branch 3
+    for len in [5, 15, 25, 35] {
+        rt.send_to(addr, ByteMessage(vec![0u8; len])).unwrap();
+    }
+    rt.tick(); // no trap in any branch
+}
+
+// Multiple sends in one handle with increasing payload sizes
+#[test]
+fn guest_sends_increasing_payloads_in_one_handle() {
+    let wat = r#"(module
+        (import "swactor" "send" (func $send (param i32 i32 i32)))
+        (memory (export "memory") 1)
+        (func (export "alloc") (param $len i32) (result i32) i32.const 1024)
+        (func (export "handle") (param $ptr i32) (param $len i32)
+            ;; Send 1 byte, 2 bytes, 3 bytes from offset 0 (with dest at ptr)
+            (if (i32.ge_u (local.get $len) (i32.const 32))
+                (then
+                    (call $send (local.get $ptr) (i32.add (local.get $ptr) (i32.const 32)) (i32.const 1))
+                    (call $send (local.get $ptr) (i32.add (local.get $ptr) (i32.const 32)) (i32.const 2))
+                    (call $send (local.get $ptr) (i32.add (local.get $ptr) (i32.const 32)) (i32.const 3))
+                )
+            )
+        )
+    )"#;
+    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();
+
+    let mut msg = Vec::new();
+    msg.extend_from_slice(&inbox.addr().0);
+    msg.extend_from_slice(b"ABCDE");
+    rt.send_to(addr, ByteMessage(msg)).unwrap();
+    rt.tick();
+
+    let msgs: Vec<Vec<u8>> = std::iter::from_fn(|| inbox.try_recv().map(|m| m.0)).collect();
+    assert_eq!(msgs.len(), 3);
+    assert_eq!(msgs[0].len(), 1);
+    assert_eq!(msgs[1].len(), 2);
+    assert_eq!(msgs[2].len(), 3);
+}
+
+// Engine and builder are independent — dropping engine after build still works
+#[test]
+fn engine_dropped_after_build_actor_still_works() {
+    let actor = {
+        let engine = SharedEngine::new().unwrap();
+        WasmActorBuilder::new(engine, guest_wasm("echo")).build().unwrap()
+        // engine dropped here
+    };
+    let rt = Runtime::new(RuntimeConfig::default());
+    let inbox = rt.new_inbox::<ByteMessage>().unwrap();
+    let addr = rt.spawn(actor).unwrap();
+    rt.send_to(addr, framed_msg(inbox.addr(), b"after-drop")).unwrap();
+    rt.tick();
+
+    let resp = inbox.try_recv().expect("should echo after engine dropped");
+    assert_eq!(resp.0, b"after-drop");
 }
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