diff --git a/crates/wasm-actor/tests/wasm_actor.rs b/crates/wasm-actor/tests/wasm_actor.rs
index afd6868..f51d2eb 100644
--- a/crates/wasm-actor/tests/wasm_actor.rs
+++ b/crates/wasm-actor/tests/wasm_actor.rs
@@ -9755,4 +9755,186 @@ fn engine_dropped_after_build_actor_still_works() {
 
     let resp = inbox.try_recv().expect("should echo after engine dropped");
     assert_eq!(resp.0, b"after-drop");
+}
+
+// ── Cycle 67 ─────────────────────────────────────────────────────────────────
+
+// Guest uses grow, then accesses the newly grown page
+#[test]
+fn guest_grows_memory_and_uses_new_page() {
+    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)
+            (local $old_pages i32)
+            ;; Grow by 1 page
+            (local.set $old_pages (memory.grow (i32.const 1)))
+            ;; Write at start of new page (old_pages * 65536)
+            (i32.store
+                (i32.mul (local.get $old_pages) (i32.const 65536))
+                (i32.const 0xDEADBEEF)
+            )
+            ;; Send from first 32 bytes of message
+            (if (i32.ge_u (local.get $len) (i32.const 32))
+                (then
+                    (call $send (local.get $ptr) (i32.const 0) (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 inbox = rt.new_inbox::<ByteMessage>().unwrap();
+    let addr = rt.spawn(actor).unwrap();
+
+    let mut msg = Vec::new();
+    msg.extend_from_slice(&inbox.addr().0);
+    rt.send_to(addr, ByteMessage(msg)).unwrap();
+    rt.tick();
+
+    // Should receive empty payload (sent 0 bytes)
+    let resp = inbox.try_recv().expect("should receive msg after grow");
+    assert!(resp.0.is_empty());
+}
+
+// Native actor receives message from WASM echo, verifies payload
+struct PayloadVerifier {
+    expected: Vec<u8>,
+    verified: std::cell::Cell<bool>,
+}
+impl ActorInterface for PayloadVerifier {
+    type Incoming = ByteMessage;
+    type Response = ();
+    fn handle(&mut self, _ctx: &Ctx, msg: ByteMessage) {
+        if msg.0 == self.expected {
+            self.verified.set(true);
+        }
+    }
+}
+
+#[test]
+fn native_verifier_receives_wasm_echo() {
+    let engine = SharedEngine::new().unwrap();
+    let echo = WasmActorBuilder::new(engine, guest_wasm("echo")).build().unwrap();
+    let rt = Runtime::new(RuntimeConfig::default());
+
+    let verifier = PayloadVerifier {
+        expected: b"hello-from-wasm".to_vec(),
+        verified: std::cell::Cell::new(false),
+    };
+    let v_addr = rt.spawn(verifier).unwrap();
+    let e_addr = rt.spawn(echo).unwrap();
+
+    rt.send_to(e_addr, framed_msg(&v_addr, b"hello-from-wasm")).unwrap();
+    rt.tick();
+    rt.tick(); // verifier processes the echoed message
+}
+
+// Sequential spawn-echo-stop for 3 different guest types
+#[test]
+fn sequential_echo_double_silent_lifecycle() {
+    let engine = SharedEngine::new().unwrap();
+    let rt = Runtime::new(RuntimeConfig::default());
+    let inbox = rt.new_inbox::<ByteMessage>().unwrap();
+
+    // Echo phase
+    let echo = WasmActorBuilder::new(engine.clone(), guest_wasm("echo")).build().unwrap();
+    let e_addr = rt.spawn(echo).unwrap();
+    rt.send_to(e_addr, framed_msg(inbox.addr(), b"E")).unwrap();
+    rt.tick();
+    assert_eq!(inbox.try_recv().unwrap().0, b"E");
+    rt.stop_actor(e_addr);
+    rt.tick();
+
+    // Double phase
+    let double = WasmActorBuilder::new(engine.clone(), guest_wasm("double")).build().unwrap();
+    let d_addr = rt.spawn(double).unwrap();
+    rt.send_to(d_addr, framed_msg(inbox.addr(), b"D")).unwrap();
+    rt.tick();
+    let d_msgs: Vec<_> = std::iter::from_fn(|| inbox.try_recv().map(|m| m.0)).collect();
+    assert_eq!(d_msgs.len(), 2);
+    rt.stop_actor(d_addr);
+    rt.tick();
+
+    // Silent phase
+    let silent = WasmActorBuilder::new(engine, guest_wasm("silent")).build().unwrap();
+    let s_addr = rt.spawn(silent).unwrap();
+    rt.send_to(s_addr, ByteMessage(b"S".to_vec())).unwrap();
+    rt.tick();
+    assert!(inbox.try_recv().is_none());
+    rt.stop_actor(s_addr);
+    rt.tick();
+}
+
+// Guest with 0 initial data pages but minimum 1 required → module with 0 pages
+#[test]
+fn module_with_zero_memory_pages_builds_but_alloc_fails_gracefully() {
+    // Can't have 0-page memory in WAT (minimum is 0 but the export needs at least some)
+    // Actually (memory 0) is valid — 0 initial pages, can grow later
+    let wat = r#"(module
+        (memory (export "memory") 0)
+        (func (export "alloc") (param $len i32) (result i32) i32.const -1)
+        (func (export "handle") (param $ptr i32) (param $len i32))
+    )"#;
+    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();
+
+    // alloc returns -1, so message is dropped (ptr < 0 check)
+    rt.send_to(addr, ByteMessage(b"test".to_vec())).unwrap();
+    rt.tick(); // no panic
+}
+
+// Double guest receives same message twice in same tick — produces 4 responses
+#[test]
+fn double_receives_two_messages_produces_four() {
+    let engine = SharedEngine::new().unwrap();
+    let double = WasmActorBuilder::new(engine, guest_wasm("double")).build().unwrap();
+    let rt = Runtime::new(RuntimeConfig::default());
+    let inbox = rt.new_inbox::<ByteMessage>().unwrap();
+    let addr = rt.spawn(double).unwrap();
+
+    rt.send_to(addr, framed_msg(inbox.addr(), b"A")).unwrap();
+    rt.send_to(addr, framed_msg(inbox.addr(), b"B")).unwrap();
+    rt.tick();
+
+    let msgs: Vec<Vec<u8>> = std::iter::from_fn(|| inbox.try_recv().map(|m| m.0)).collect();
+    assert_eq!(msgs.len(), 4, "2 messages × 2 copies each = 4");
+    // First two are copies of "A", last two are copies of "B"
+    assert_eq!(msgs[0], b"A");
+    assert_eq!(msgs[1], b"A");
+    assert_eq!(msgs[2], b"B");
+    assert_eq!(msgs[3], b"B");
+}
+
+// Property: stopping an actor never panics regardless of pending messages
+proptest! {
+    #[test]
+    fn prop_stop_with_pending_never_panics(
+        n_msgs in 0usize..50,
+        ticks_before_stop in 0usize..5,
+        ticks_after_stop in 1usize..5,
+    ) {
+        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 0..n_msgs {
+            let _ = rt.send_to(addr, ByteMessage(vec![i as u8; 10]));
+        }
+        for _ in 0..ticks_before_stop {
+            rt.tick();
+        }
+        rt.stop_actor(addr);
+        for _ in 0..ticks_after_stop {
+            rt.tick();
+        }
+    }
 }
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