test(wasm-actor): cycle 91 — double-byte saturate, 20 MT actors, 100KB OOB (414 tests)

Added 4 tests: double each byte with saturation, 20 echo actors on 2-thread
runtime, 5-page memory spread alloc, 100KB payload dropped for 1-page guest
(verifies graceful OOB handling). No new bugs found.

Authored by Claude, lovingly guided by Zachery Aaron Shores-Chmielewski

crates/wasm-actor/tests/wasm_actor.rs

@@ -13091,3 +13091,128 @@ fn echo_exactly_thirty_three_bytes() {
     let resp = inbox.try_recv().expect("single byte payload echo");
     assert_eq!(resp.0, vec![0x42]);
 }
+
+// ── Cycle 91 ─────────────────────────────────────────────────────────────────
+
+// Guest that doubles each byte value (saturating at 255)
+#[test]
+fn guest_doubles_each_byte_saturating() {
+    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 $i i32)
+            (local $val i32)
+            (if (i32.lt_u (local.get $len) (i32.const 33)) (then return))
+            ;; Double each byte in payload, saturate at 255
+            (local.set $i (i32.const 32))
+            (block $exit
+                (loop $loop
+                    (br_if $exit (i32.ge_u (local.get $i) (local.get $len)))
+                    (local.set $val
+                        (i32.mul (i32.load8_u (i32.add (local.get $ptr) (local.get $i))) (i32.const 2)))
+                    (if (i32.gt_u (local.get $val) (i32.const 255))
+                        (then (local.set $val (i32.const 255)))
+                    )
+                    (i32.store8
+                        (i32.add (local.get $ptr) (local.get $i))
+                        (local.get $val))
+                    (local.set $i (i32.add (local.get $i) (i32.const 1)))
+                    (br $loop)
+                )
+            )
+            (call $send (local.get $ptr)
+                (i32.add (local.get $ptr) (i32.const 32))
+                (i32.sub (local.get $len) (i32.const 32)))
+        )
+    )"#;
+    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();
+
+    rt.send_to(addr, framed_msg(inbox.addr(), &[10, 100, 200])).unwrap();
+    rt.tick();
+
+    let resp = inbox.try_recv().expect("doubled response");
+    assert_eq!(resp.0, vec![20, 200, 255], "200*2=400 capped at 255");
+}
+
+// 20 echo actors on a 2-thread runtime
+#[test]
+fn twenty_echo_actors_two_threads() {
+    let engine = SharedEngine::new().unwrap();
+    let mut cfg = RuntimeConfig::default();
+    cfg.num_threads = 2;
+    let rt = Runtime::new(cfg);
+    let inbox = rt.new_inbox::<ByteMessage>().unwrap();
+
+    for i in 0..20u8 {
+        let actor = WasmActorBuilder::new(engine.clone(), guest_wasm("echo")).build().unwrap();
+        let addr = rt.spawn(actor).unwrap();
+        rt.send_to(addr, framed_msg(inbox.addr(), &[i])).unwrap();
+    }
+
+    let handle = rt.run().unwrap();
+    let mut total = 0;
+    for _ in 0..100 {
+        total += std::iter::from_fn(|| inbox.try_recv()).count();
+        if total >= 20 { break; }
+        std::thread::sleep(std::time::Duration::from_millis(50));
+    }
+    handle.shutdown();
+    assert_eq!(total, 20, "all 20 actors echoed on 2-thread runtime");
+}
+
+// Guest with 5 pages memory — alloc at various offsets
+#[test]
+fn guest_five_page_memory_with_spread_alloc() {
+    let wat = r#"(module
+        (memory (export "memory") 5)
+        (global $next (mut i32) (i32.const 65536))
+        (func (export "alloc") (param $len i32) (result i32)
+            (local $ptr i32)
+            (local.set $ptr (global.get $next))
+            (global.set $next (i32.add (global.get $next) (local.get $len)))
+            (local.get $ptr)
+        )
+        (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 starts at page 2, spreading across pages
+    for _ in 0..20 {
+        rt.send_to(addr, ByteMessage(vec![0; 5000])).unwrap();
+    }
+    rt.tick();
+}
+
+// 100KB payload too large for 1-page echo guest — message dropped gracefully
+#[test]
+fn hundred_kb_payload_dropped_for_one_page_guest() {
+    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();
+
+    let payload: Vec<u8> = (0..100_000u32).map(|i| (i % 251) as u8).collect();
+    rt.send_to(addr, framed_msg(inbox.addr(), &payload)).unwrap();
+    rt.tick();
+
+    // Echo guest has 1 page (64KB) — 100KB payload can't be allocated
+    // Message should be dropped gracefully (OOB bounds check)
+    assert!(inbox.try_recv().is_none(), "100KB too large for 1-page guest");
+
+    // Actor should still be alive — send a small message
+    rt.send_to(addr, framed_msg(inbox.addr(), b"alive")).unwrap();
+    rt.tick();
+    assert_eq!(inbox.try_recv().unwrap().0, b"alive");
+}