diff --git a/crates/wasm-actor/tests/wasm_actor.rs b/crates/wasm-actor/tests/wasm_actor.rs
index c4f37b6..4dcbf5f 100644
--- a/crates/wasm-actor/tests/wasm_actor.rs
+++ b/crates/wasm-actor/tests/wasm_actor.rs
@@ -11854,4 +11854,138 @@ fn echo_single_byte_payload_integrity() {
     for (i, &b) in responses.iter().enumerate() {
         assert_eq!(b, i as u8);
     }
+}
+
+// ── Cycle 83 ─────────────────────────────────────────────────────────────────
+
+// Spawn echo, send 1000 messages, verify all received over multiple ticks
+#[test]
+fn thousand_message_echo_stress() {
+    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 0u16..1000 {
+        rt.send_to(addr, framed_msg(inbox.addr(), &i.to_le_bytes())).unwrap();
+    }
+    for _ in 0..50 {
+        rt.tick();
+    }
+
+    let count = std::iter::from_fn(|| inbox.try_recv()).count();
+    assert_eq!(count, 1000, "all 1000 messages echoed");
+}
+
+// Guest with type annotations on all locals (verbose WAT)
+#[test]
+fn guest_with_many_typed_locals() {
+    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)
+            (local $a i32) (local $b i32) (local $c i32)
+            (local $d i64) (local $e f32) (local $f f64)
+            (local.set $a (local.get $len))
+            (local.set $b (i32.mul (local.get $a) (i32.const 2)))
+            (local.set $c (i32.add (local.get $a) (local.get $b)))
+            (local.set $d (i64.extend_i32_u (local.get $c)))
+            (local.set $e (f32.convert_i32_s (local.get $c)))
+            (local.set $f (f64.promote_f32 (local.get $e)))
+            (i32.store (local.get $ptr) (local.get $c))
+        )
+    )"#;
+    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![0u8; 4])).unwrap();
+    rt.tick();
+}
+
+// Same actor handles empty and non-empty messages alternately
+#[test]
+fn alternate_empty_and_nonempty_messages() {
+    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..10 {
+        if i % 2 == 0 {
+            rt.send_to(addr, ByteMessage(vec![])).unwrap(); // empty
+        } else {
+            rt.send_to(addr, framed_msg(inbox.addr(), &[i as u8])).unwrap();
+        }
+    }
+    rt.tick();
+
+    // Only the non-empty framed messages should produce echo responses
+    let msgs: Vec<Vec<u8>> = std::iter::from_fn(|| inbox.try_recv().map(|m| m.0)).collect();
+    assert_eq!(msgs.len(), 5, "5 framed messages echoed");
+}
+
+// WasmActorError variants have distinct Display representations
+#[test]
+fn error_variants_have_distinct_display() {
+    let missing = WasmActorError::MissingExport("memory");
+    let wasmtime_err = WasmActorError::Wasmtime(wasmtime::Error::msg("test error"));
+
+    let s1 = format!("{missing}");
+    let s2 = format!("{wasmtime_err}");
+
+    assert_ne!(s1, s2, "error variants should have different display");
+    assert!(s1.contains("memory"));
+    assert!(s2.contains("test error"));
+}
+
+// Two different WAT modules on same runtime — heterogeneous actors
+#[test]
+fn heterogeneous_wat_actors_on_same_runtime() {
+    // Actor 1: echoes
+    let wat_echo = 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)
+            (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))))))
+    )"#;
+    // Actor 2: always sends byte 0x42
+    let wat_const = r#"(module
+        (import "swactor" "send" (func $send (param i32 i32 i32)))
+        (memory (export "memory") 1)
+        (data (i32.const 900) "\42")
+        (func (export "alloc") (param $len i32) (result i32) i32.const 1024)
+        (func (export "handle") (param $ptr i32) (param $len i32)
+            (if (i32.ge_u (local.get $len) (i32.const 32))
+                (then (call $send (local.get $ptr) (i32.const 900) (i32.const 1)))))
+    )"#;
+
+    let engine = SharedEngine::new().unwrap();
+    let a1 = WasmActorBuilder::new(engine.clone(), wat::parse_str(wat_echo).unwrap())
+        .build().unwrap();
+    let a2 = WasmActorBuilder::new(engine, wat::parse_str(wat_const).unwrap())
+        .build().unwrap();
+
+    let rt = Runtime::new(RuntimeConfig::default());
+    let inbox = rt.new_inbox::<ByteMessage>().unwrap();
+    let addr1 = rt.spawn(a1).unwrap();
+    let addr2 = rt.spawn(a2).unwrap();
+
+    rt.send_to(addr1, framed_msg(inbox.addr(), b"hello")).unwrap();
+    let mut msg2 = Vec::new();
+    msg2.extend_from_slice(&inbox.addr().0);
+    rt.send_to(addr2, ByteMessage(msg2)).unwrap();
+    rt.tick();
+
+    let msgs: Vec<Vec<u8>> = std::iter::from_fn(|| inbox.try_recv().map(|m| m.0)).collect();
+    assert_eq!(msgs.len(), 2);
+    // One is "hello", other is [0x42]
+    assert!(msgs.iter().any(|m| m == b"hello"));
+    assert!(msgs.iter().any(|m| m == &[0x42]));
 }
\ No newline at end of file