diff --git a/crates/wasm-actor/tests/wasm_actor.rs b/crates/wasm-actor/tests/wasm_actor.rs
index 9f763ae..208fe40 100644
--- a/crates/wasm-actor/tests/wasm_actor.rs
+++ b/crates/wasm-actor/tests/wasm_actor.rs
@@ -6929,4 +6929,220 @@ fn idle_ticks_dont_affect_wasm_actor() {
 
     let msg = inbox.try_recv().unwrap();
     assert_eq!(msg.0, b"after-idle");
+}
+
+// ── WASM + native actors alternate processing in same tick ──────────────────
+
+#[test]
+fn wasm_and_native_alternate_in_same_tick() {
+    struct NativeEcho2;
+    impl ActorInterface for NativeEcho2 {
+        type Incoming = ByteMessage;
+        type Response = ();
+        fn handle(&mut self, ctx: &Ctx, msg: ByteMessage) {
+            if msg.0.len() >= 32 {
+                let mut addr_bytes = [0u8; 32];
+                addr_bytes.copy_from_slice(&msg.0[..32]);
+                let dest = ActorAddress(addr_bytes);
+                let payload = msg.0[32..].to_vec();
+                let _ = ctx.send(dest, ByteMessage(payload));
+            }
+        }
+    }
+
+    let engine = SharedEngine::new().unwrap();
+    let wasm_echo = WasmActorBuilder::new(engine, guest_wasm("echo")).build().unwrap();
+
+    let rt = Runtime::new(RuntimeConfig::default());
+    let inbox = rt.new_inbox::<ByteMessage>().unwrap();
+    let wasm_addr = rt.spawn(wasm_echo).unwrap();
+    let native_addr = rt.spawn(NativeEcho2).unwrap();
+
+    for i in 0u8..10 {
+        if i % 2 == 0 {
+            rt.send_to(wasm_addr, framed_msg(inbox.addr(), &[i])).unwrap();
+        } else {
+            rt.send_to(native_addr, framed_msg(inbox.addr(), &[i])).unwrap();
+        }
+    }
+    rt.tick();
+
+    let mut received = Vec::new();
+    while let Some(msg) = inbox.try_recv() {
+        received.push(msg.0[0]);
+    }
+    received.sort();
+    let expected: Vec<u8> = (0..10).collect();
+    assert_eq!(received, expected, "all 10 messages from both types should deliver");
+}
+
+// ── Guest sums two payload bytes ────────────────────────────────────────────
+
+#[test]
+fn guest_sums_two_payload_bytes() {
+    let wat = r#"
+        (module
+            (import "swactor" "send" (func $send (param i32 i32 i32)))
+            (memory (export "memory") 1)
+            (func (export "alloc") (param i32) (result i32) i32.const 4096)
+            (func (export "handle") (param $ptr i32) (param $len i32)
+                (local $val i32)
+                (local.set $val
+                    (i32.add
+                        (i32.load8_u (i32.add (local.get $ptr) (i32.const 32)))
+                        (i32.load8_u (i32.add (local.get $ptr) (i32.const 33)))
+                    )
+                )
+                (i32.store8 (i32.const 200) (local.get $val))
+                (i32.store8 (i32.const 201) (local.get $val))
+                (call $send (local.get $ptr) (i32.const 200) (i32.const 2))
+            )
+        )
+    "#;
+    let wasm = wat::parse_str(wat).unwrap();
+    let engine = SharedEngine::new().unwrap();
+    let actor = WasmActorBuilder::new(engine, wasm).build().unwrap();
+
+    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(), &[30, 12])).unwrap();
+    rt.tick();
+
+    let msg = inbox.try_recv().unwrap();
+    assert_eq!(msg.0, vec![42, 42], "30+12=42 duplicated");
+}
+
+// ── Single byte payload echo ────────────────────────────────────────────────
+
+#[test]
+fn single_byte_payload_echo() {
+    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();
+
+    rt.send_to(addr, framed_msg(inbox.addr(), &[0x42])).unwrap();
+    rt.tick();
+
+    let msg = inbox.try_recv().unwrap();
+    assert_eq!(msg.0, vec![0x42]);
+}
+
+// ── Module with no functions fails ──────────────────────────────────────────
+
+#[test]
+fn module_with_no_functions_fails() {
+    let wat = "(module (memory (export \"memory\") 1))";
+    let wasm = wat::parse_str(wat).unwrap();
+    let engine = SharedEngine::new().unwrap();
+    assert!(WasmActorBuilder::new(engine, wasm).build().is_err());
+}
+
+// ── Response varies by message size ─────────────────────────────────────────
+
+#[test]
+fn response_varies_by_message_size() {
+    let wat = r#"
+        (module
+            (import "swactor" "send" (func $send (param i32 i32 i32)))
+            (memory (export "memory") 1)
+            (func (export "alloc") (param i32) (result i32) i32.const 4096)
+            (func (export "handle") (param $ptr i32) (param $len i32)
+                (i32.store8 (i32.const 200) (i32.sub (local.get $len) (i32.const 32)))
+                (call $send (local.get $ptr) (i32.const 200) (i32.const 1))
+            )
+        )
+    "#;
+    let wasm = wat::parse_str(wat).unwrap();
+    let engine = SharedEngine::new().unwrap();
+    let actor = WasmActorBuilder::new(engine, wasm).build().unwrap();
+
+    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(), &[])).unwrap();
+    rt.send_to(addr, framed_msg(inbox.addr(), &[1])).unwrap();
+    rt.send_to(addr, framed_msg(inbox.addr(), &[0; 50])).unwrap();
+    rt.send_to(addr, framed_msg(inbox.addr(), &[0; 200])).unwrap();
+    rt.tick();
+
+    let sizes: Vec<u8> = std::iter::from_fn(|| inbox.try_recv().map(|m| m.0[0])).collect();
+    assert_eq!(sizes, vec![0, 1, 50, 200]);
+}
+
+// ── Property: echo is deterministic ─────────────────────────────────────────
+
+proptest! {
+    #[test]
+    fn prop_echo_is_deterministic(
+        payload in proptest::collection::vec(proptest::num::u8::ANY, 0..128)
+    ) {
+        let engine = SharedEngine::new().unwrap();
+        let rt = Runtime::new(RuntimeConfig::default());
+        let inbox = rt.new_inbox::<ByteMessage>().unwrap();
+
+        let actor1 = WasmActorBuilder::new(engine.clone(), guest_wasm("echo")).build().unwrap();
+        let addr1 = rt.spawn(actor1).unwrap();
+        rt.send_to(addr1, framed_msg(inbox.addr(), &payload)).unwrap();
+        rt.tick();
+        let result1 = inbox.try_recv().map(|m| m.0);
+
+        let actor2 = WasmActorBuilder::new(engine, guest_wasm("echo")).build().unwrap();
+        let addr2 = rt.spawn(actor2).unwrap();
+        rt.send_to(addr2, framed_msg(inbox.addr(), &payload)).unwrap();
+        rt.tick();
+        let result2 = inbox.try_recv().map(|m| m.0);
+
+        assert_eq!(result1, result2, "same input should produce same output");
+    }
+}
+
+// ── 200th test: comprehensive lifecycle with all guest types ────────────────
+
+#[test]
+fn comprehensive_lifecycle_all_guest_types_200th() {
+    // Spawn one of each guest type (echo, double, silent), send messages,
+    // verify outputs, stop them all, check cleanup.
+    let engine = SharedEngine::new().unwrap();
+    let echo = WasmActorBuilder::new(engine.clone(), guest_wasm("echo")).build().unwrap();
+    let double = WasmActorBuilder::new(engine.clone(), guest_wasm("double")).build().unwrap();
+    let silent = WasmActorBuilder::new(engine, guest_wasm("silent")).build().unwrap();
+
+    let rt = Runtime::new(RuntimeConfig::default());
+    let inbox = rt.new_inbox::<ByteMessage>().unwrap();
+
+    let echo_addr = rt.spawn(echo).unwrap();
+    let double_addr = rt.spawn(double).unwrap();
+    let silent_addr = rt.spawn(silent).unwrap();
+
+    // Send to all three
+    rt.send_to(echo_addr, framed_msg(inbox.addr(), b"E")).unwrap();
+    rt.send_to(double_addr, framed_msg(inbox.addr(), b"D")).unwrap();
+    rt.send_to(silent_addr, framed_msg(inbox.addr(), b"S")).unwrap();
+    rt.tick();
+
+    let mut payloads: Vec<Vec<u8>> = Vec::new();
+    while let Some(msg) = inbox.try_recv() {
+        payloads.push(msg.0);
+    }
+    payloads.sort();
+    // Echo → "E" (1x), Double → "D" (2x), Silent → nothing
+    assert_eq!(payloads, vec![b"D".to_vec(), b"D".to_vec(), b"E".to_vec()]);
+
+    // Stop all
+    rt.stop_actor(echo_addr);
+    rt.stop_actor(double_addr);
+    rt.stop_actor(silent_addr);
+    rt.tick();
+    rt.tick();
+
+    // Send to stopped actors — silently dropped
+    rt.send_to(echo_addr, framed_msg(inbox.addr(), b"gone")).ok();
+    rt.tick();
+    assert!(inbox.try_recv().is_none(), "stopped actors should not deliver");
 }
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