diff --git a/crates/wasm-actor/tests/wasm_actor.rs b/crates/wasm-actor/tests/wasm_actor.rs
index afa613f..d20957e 100644
--- a/crates/wasm-actor/tests/wasm_actor.rs
+++ b/crates/wasm-actor/tests/wasm_actor.rs
@@ -3980,3 +3980,132 @@ fn wasm_actor_is_send() {
     fn assert_send<T: Send>() {}
     assert_send::<WasmActor>();
 }
+
+// ── Guest writes to alloc pointer region before sending ─────────────────────
+
+#[test]
+fn guest_modifies_received_message_before_echoing() {
+    // Guest receives a message, XORs each payload byte with 0xFF, then
+    // echoes the modified payload. Verifies that the guest can mutate
+    // linear memory and the modified data is what gets sent.
+    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 $i i32)
+                (local $payload_start i32)
+                (local $payload_len i32)
+
+                ;; payload starts at ptr+32, length is len-32
+                (local.set $payload_start (i32.add (local.get $ptr) (i32.const 32)))
+                (local.set $payload_len (i32.sub (local.get $len) (i32.const 32)))
+
+                ;; Skip if no payload
+                (br_if 0 (i32.lt_s (local.get $payload_len) (i32.const 1)))
+
+                ;; XOR each byte with 0xFF
+                (local.set $i (i32.const 0))
+                (block $break
+                    (loop $loop
+                        (br_if $break (i32.ge_u (local.get $i) (local.get $payload_len)))
+                        (i32.store8
+                            (i32.add (local.get $payload_start) (local.get $i))
+                            (i32.xor
+                                (i32.load8_u (i32.add (local.get $payload_start) (local.get $i)))
+                                (i32.const 255)
+                            )
+                        )
+                        (local.set $i (i32.add (local.get $i) (i32.const 1)))
+                        (br $loop)
+                    )
+                )
+
+                ;; Send modified payload
+                local.get $ptr
+                local.get $payload_start
+                local.get $payload_len
+                call $send
+            )
+        )
+    "#;
+    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();
+
+    let payload = vec![0x00, 0x0F, 0xF0, 0xFF];
+    rt.send_to(addr, framed_msg(inbox.addr(), &payload)).unwrap();
+    rt.tick();
+
+    let received = inbox.try_recv().expect("XOR transform should send");
+    let expected: Vec<u8> = payload.iter().map(|b| b ^ 0xFF).collect();
+    assert_eq!(received.0, expected, "payload should be XOR'd with 0xFF");
+}
+
+// ── Stop and re-spawn at same conceptual slot ───────────────────────────────
+
+#[test]
+fn stop_and_respawn_same_type_repeatedly() {
+    // Stop and respawn the same type of WASM actor 5 times.
+    // Each new instance should work independently.
+    let engine = SharedEngine::new().unwrap();
+    let wasm_bytes = guest_wasm("echo");
+    let rt = Runtime::new(RuntimeConfig::default());
+    let inbox = rt.new_inbox::<ByteMessage>().unwrap();
+
+    for round in 0u8..5 {
+        let actor = WasmActorBuilder::new(engine.clone(), wasm_bytes.clone())
+            .build().unwrap();
+        let addr = rt.spawn(actor).unwrap();
+
+        rt.send_to(addr, framed_msg(inbox.addr(), &[round])).unwrap();
+        rt.tick();
+        let received = inbox.try_recv().expect("respawned actor should echo");
+        assert_eq!(received.0, vec![round]);
+
+        rt.stop_actor(addr).unwrap();
+        rt.tick();
+        rt.tick();
+    }
+}
+
+// ── WASM actor watches another WASM actor ───────────────────────────────────
+// Note: WasmActor doesn't implement on_actor_exit, so watch notifications
+// are received but unhandled (default no-op). The important thing is no crash.
+
+#[test]
+fn wasm_actor_watching_another_wasm_actor_doesnt_crash() {
+    // Two WASM actors. We can't make one watch the other through the WASM
+    // ABI (ctx.watch isn't exposed to guests). But we can have a native
+    // watcher confirm the runtime handles WASM actors in the watch system.
+    // (Already covered by native_watcher_notified_when_wasm_actor_stops,
+    // but let's verify with two WASM actors dying in sequence.)
+    let engine = SharedEngine::new().unwrap();
+    let wasm_bytes = guest_wasm("silent");
+
+    let actor_a = WasmActorBuilder::new(engine.clone(), wasm_bytes.clone()).build().unwrap();
+    let actor_b = WasmActorBuilder::new(engine, wasm_bytes).build().unwrap();
+
+    let rt = Runtime::new(RuntimeConfig::default());
+    let addr_a = rt.spawn(actor_a).unwrap();
+    let addr_b = rt.spawn(actor_b).unwrap();
+    rt.tick();
+
+    // Stop both in sequence
+    rt.stop_actor(addr_a).unwrap();
+    rt.tick();
+    rt.tick();
+
+    rt.stop_actor(addr_b).unwrap();
+    rt.tick();
+    rt.tick();
+
+    // Both gone, no crash
+    assert!(rt.send_to(addr_a, ByteMessage(vec![1])).is_err());
+    assert!(rt.send_to(addr_b, ByteMessage(vec![1])).is_err());
+}