test: Cycle 40 — pre-filled memory, engine clone, i64 ops, 200-actor stress

- guest_start_function_modifies_alloc_region: host overwrites pre-filled 0xFF memory
- engine_clone_is_same_engine: cloned engine produces working actors
- handle_uses_i64_operations: i64 arithmetic with i32.wrap_i64
- two_hundred_actors_from_same_engine: 200 actors all process one message
- Updated history.md with Cycles 27-39

All 170 tests pass. No new bugs found.

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

CLAUDE/notes/history.md

@@ -0,0 +1,194 @@
+# Cycle History (append-only)
+
+## Cycle 0 — Research
+- Read WASM runner implementation end-to-end (5 source files, 3 guest modules, 11 tests)
+- Wrote feature_map.md, constraints.md, research_synthesis.md (15 ranked test scenarios)
+- Found potential bug P0-1: missing bounds check in actor.rs:44-46 (copy_from_slice OOB)
+- Built guest WASM modules, verified all 11 baseline tests pass
+
+## Cycle 1 — P0/P1/P2 Tests + 2 Bug Fixes
+- Wrote 12 new tests (P0-1 through P2-1), total now 23
+- Bug #1 fixed: actor.rs bounds check — alloc OOB ptr caused permanent actor poisoning
+- Bug #2 found+fixed: worker.rs StopSignal didn't push to deaths — watchers never notified for stop_actor()
+- All 23 WASM actor tests + 157 core tests pass
+
+## Cycle 2 — P2-2 + P3 Property Tests
+- Added multi-worker runtime test (P2-2) — Send safety of wasmtime Store verified
+- Added 2 property-based tests (proptest): echo round-trip + double 2x invariant
+- All 26 WASM actor tests pass, all scenarios from research_synthesis.md complete
+
+## Cycle 3 — Deep Dive: Stale Outbox + Edge Cases
+- Bug #3 found+fixed: outbox not cleared on handle trap — stale sends leaked into next call
+- Added 4 new tests: stale outbox leak, invalid WASM bytes, zero-length payload send, multiple sequential traps
+- All 30 tests pass
+
+## Cycle 4 — Start Trap, Self-Send, Amplification, Overlap
+- Added 4 more tests: trapping start function, self-send feedback loop, 10x amplification, overlapping send regions
+- No new bugs found (all 4 pass)
+- All 34 tests pass
+
+## Cycle 5 — Type Mismatch, State Persistence, Dynamic Spawn
+- Added 3 tests: type mismatch handling, guest mutable state persistence, dynamic WASM spawn from handler
+- No new bugs found
+- All 37 tests pass
+
+## Cycle 6 — Bounded Mailbox + Alloc Fuzzing
+- Added bounded mailbox backpressure test (DropNewest policy)
+- Added property test: any alloc return value (-100..70000) never kills actor
+- All 39 tests pass
+
+## Cycle 7 — Alloc Trap, memory.grow, Send Overflow, Exact-Fit
+- Added 4 tests: alloc trapping (store recovery), memory.grow during handle, send with dest_ptr=i32::MAX overflow, exact-fit allocation at boundary
+- No new bugs found — all edge cases handled correctly
+- All 43 tests pass
+
+## Cycle 8 — Off-By-One, Lifecycle, Chains, Grow Exhaust
+- Added 5 tests: alloc returns exactly memory size, spawn-stop without messages, 3-hop relay, 10-hop chain relay, memory.grow until failure
+- No new bugs found
+- All 48 tests pass
+
+## Cycle 9 — Send Overflow/Boundary, Cross-Thread, Fuzz Send Args
+- Added 4 tests: payload range overflow, payload at exact memory end, cross-thread WASM relay, property test fuzzing all send args
+- No new bugs found
+- All 52 tests pass
+
+## Cycle 10 — Multi-Dest Sends, Outbox Copy, Large Payload, Alloc-with-Grow
+- Added 4 tests: two destinations in one handle, memory overwrite after send (outbox copy safety), large payload, alloc that grows memory returns new region pointer
+- No new bugs found
+- All 56 tests pass
+
+## Cycle 11 — Message Budget, Data Segments, Outbox Isolation, Combined Fuzz
+- Added 4 tests: actor_message_budget fairness, data segment initialized memory, two-actor outbox isolation, combined alloc+trap+send property fuzz
+- No new bugs found — prop_random_module_behavior_never_crashes is strongest general safety property
+- All 60 tests pass
+
+## Cycle 12 — Stack Overflow, Bulk Memory, Self-Amplification, Double Stop
+- Added 4 tests: infinite recursion trap, bulk memory.fill, self-amplification bounded by budget, double stop idempotency
+- Fixed 2 flaky MT tests (poll with retry loop instead of fixed sleep)
+- All 64 tests pass
+
+## Cycle 13 — SIMD Rejection, Garbage Address, call_indirect, Custom Sections
+- Added 5 tests: SIMD module rejected by sandboxed engine, garbage address bytes silently dropped, call_indirect dispatch, alloc returning 0 for zero-length message, custom section tolerance
+- Subtle Ok(0) guard behavior verified: alloc returns 0 + len=0 falls through to handle(0,0)
+- All 69 tests pass
+
+## Cycle 14 — Multi-Engine, Error Formatting, Rapid Lifecycle, Stop-Send Race
+- Added 6 tests: actors from different engines coexist, error Display formatting, rapid spawn-process-stop (20 iterations), stop-send race, SharedEngine Debug, ByteMessage traits
+- No new bugs found
+- All 75 tests pass
+
+## Cycle 15 — Outbox Flood, Mixed Cleanup, i32::MAX Alloc, Size Fuzz
+- Added 4 tests: 1000-message outbox flood, interleaved WASM+native actor cleanup, alloc returning i32::MAX, property test for varied payload sizes
+- No new bugs found
+- All 79 tests pass (6 property tests)
+
+## Cycle 16 — Spawn+Send Same Tick, 21-Actor Mixed Runtime, Alternating Alloc
+- Added 3 tests: message delivery on spawn tick, 20 native + 1 WASM actor mixed runtime, alloc alternating -1/256
+- No new bugs found
+- All 82 tests pass
+
+## Cycle 17 — Truncated WASM, No-Import Module, 4-Thread Stress, i32::MIN, Dual Watcher
+- Added 5 tests: truncated binary, module without send import, 10 actors on 4 threads, i32::MIN alloc, two watchers on same target
+- No new bugs found
+- All 87 tests pass
+
+## Cycle 18 — Div-by-Zero, Extra Exports, Zero-Addr, Operation Sequence Fuzz
+- Added 4 tests: division by zero trap, extra exports tolerated, zero-address send, operation sequence property fuzz
+- No new bugs found
+- All 91 tests pass
+
+## Cycle 19 — Integer Overflow Wrapping, Multi-Msg Per Tick, Hot-Swap
+- Added 3 tests: i32 overflow wrapping, 5 messages in one tick, stop echo + spawn double hot-swap
+- No new bugs found
+- All 94 tests pass
+
+## Cycle 20 — memory.copy, 50-Actor Stress, Payload Integrity, Lifecycle Fuzz
+- Added 4 tests: memory.copy bulk ops, 50 actors from same engine, pattern integrity check, lifecycle fuzz with random stopping
+- No new bugs found
+- All 98 tests pass (8 property tests)
+
+## Cycle 21 — OOB call_indirect, All-Guest Integration (100 Tests)
+- Added 2 tests: OOB table index trap, comprehensive all-guest-module integration
+- No new bugs found
+- **100 tests pass milestone** — 3 bugs found and fixed total, 8 property tests, 2 flaky MT tests fixed
+
+## Cycle 22 — OOB memory.fill, Inline Spawn+Send, Sequential Build
+- Added 3 tests: OOB memory.fill trap, native spawns WASM + sends in same handler, 10 sequential build-use-stop cycles
+- All 103 tests pass
+
+## Cycle 23 — Conditional Send, Multi-Page, 500-Message Load
+- Added 3 tests: conditional send based on payload content, 4-page initial memory, 500-message sustained load with integrity check
+- All 106 tests pass
+
+## Cycle 24 — Mass Spawn/Stop, Echo-to-Stopping, Trait Checks
+- Added 4 tests: mass spawn/stop of 100 actors, echo to stopping actor, SharedEngine Send+Sync check, WasmActor Send check
+- All 110 tests pass
+
+## Cycle 25 — XOR Transform, Stop-Respawn, Sequential Shutdown
+- Added 3 tests: in-place XOR byte transform, stop-respawn 5 rounds, sequential WASM actor shutdown
+- All 113 tests pass
+
+## Cycle 26 — Ptr/Len Verification, Double with Empty Payload
+- Added 3 tests: guest receives correct len parameter, correct ptr parameter, double with 0-byte payload
+- All 116 tests pass
+
+## Cycle 27 — Mixed Outbox, Drop-Oldest, Full Inbox
+- Added 3 tests: mixed outbox partial delivery, DropOldest mailbox policy, echo to full inbox
+- All 119 tests pass
+
+## Cycle 28 — Budget-Bounded Echoes, Wrong Signatures, Overlapping Send
+- Added 4 tests: budget limits per-tick processing, alloc wrong signature rejected, handle wrong return rejected, overlapping dest+payload
+- All 123 tests pass
+
+## Cycle 29 — Unexported Memory, Multi-Value, Send Boundary
+- Added 4 tests: memory not exported, multi-value rejected, send dest at exact boundary, send dest 1 past boundary
+- All 127 tests pass
+
+## Cycle 30 — Reftype Rejection, Trap Isolation, Negative Alloc, Global Counter
+- Added 4 tests: externref rejected, trap doesn't affect sibling, negative alloc drops, global counter persists
+- All 131 tests pass
+
+## Cycle 31 — Zero-Length Send, Separate Engines, 50-Round Stress, Start Function
+- Added 4 tests: zero-length payload delivers, two engines coexist, 50 spawn-send-stop rounds, start function init
+- All 135 tests pass
+
+## Cycle 32 — Random Payload Fuzz, Multi-Page Data, Conditional Fan-Out, Advancing Alloc
+- Added 4 tests (1 property): random payloads never panic, data segments across 3 pages, command-byte dispatch, proper bump allocator
+- All 139 tests pass
+
+## Cycle 33 — Outbox Snapshot, Grow-Per-Alloc, Trap-After-Send, Offset-Zero Send
+- Added 4 tests: outbox snapshots at send time, memory.grow per alloc, trap clears valid outbox entries, offset 0 valid
+- All 143 tests pass
+
+## Cycle 34 — From<wasmtime::Error>, 2-Thread 3-Actor MT, If/Else Branching
+- Added 3 tests: From conversion, 3 WASM actors on 2 threads, if/else dispatch
+- All 146 tests pass
+
+## Cycle 35 — Loop Sum, dest_ptr=0, Stop-With-Pending, Truncated WASM Fuzz
+- Added 4 tests (1 property): loop-based byte sum, dest_ptr=0 valid, stop with pending msgs, truncated WASM never panics
+- All 150 tests pass
+
+## Cycle 36 — FIFO Ordering, Payload Overflow, 100-Send Burst, br_table
+- Added 4 tests: message FIFO order, payload ptr overflow traps, 100 sends in one handle, br_table dispatch
+- Fixed prop_truncated_wasm test (renamed, relaxed assertion)
+- All 154 tests pass
+
+## Cycle 37 — Mutual Watch, Select Instr, WASM-WASM-Native Relay, Dest Addr Fuzz
+- Added 4 tests (1 property): watcher notified on stop, select instruction, 3-layer relay, arbitrary dest address
+- All 158 tests pass
+
+## Cycle 38 — Native Spawns WASM, Many Locals, 1000 Ticks, Send-To-Dead
+- Added 4 tests: native handler spawns WASM, 4-local arithmetic, 1000+ tick survival, send to dead actor
+- All 162 tests pass
+
+## Cycle 39 — Static Alloc Overwrite, Nested Blocks, memory.size, Spawn-Stop Fuzz
+- Added 4 tests (1 property): same ptr overwrite, nested block/br, memory.size instruction, lifecycle fuzz
+- All 166 tests pass
+
+## Campaign Summary (ongoing)
+- **44 commits** on bin-runner branch (3 bug fixes + 41 test commits)
+- **166 tests** (151 scenario + 12 property + 3 compile-time checks)
+- **3 bugs found and fixed** in core WASM actor code and runtime
+- **2 flaky MT tests fixed** with retry polling
+- **~6,100 lines** of test code
+- Implementation proved extremely robust after initial 3 bug fixes

crates/wasm-actor/tests/wasm_actor.rs

@@ -6124,3 +6124,139 @@ proptest! {
         while let Some(_) = inbox.try_recv() {}
     }
 }
+
+// ── Guest modifies memory between alloc and handle being called ─────────────
+
+#[test]
+fn guest_start_function_modifies_alloc_region() {
+    // Guest's start function writes data in the alloc region (4096+).
+    // When handle is called, the host writes over it. Tests that
+    // the host always writes fresh data, not relying on zeroed memory.
+    let wat = r#"
+        (module
+            (import "swactor" "send" (func $send (param i32 i32 i32)))
+            (memory (export "memory") 1)
+            ;; Pre-fill region at 4096 with 0xFF bytes via data segment
+            (data (i32.const 4096) "\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff\ff")
+
+            (func (export "alloc") (param i32) (result i32) i32.const 4096)
+            (func (export "handle") (param $ptr i32) (param $len i32)
+                ;; Echo payload to dest — host wrote message at 4096, overwriting 0xFF
+                (call $send
+                    (local.get $ptr)
+                    (i32.add (local.get $ptr) (i32.const 32))
+                    (i32.sub (local.get $len) (i32.const 32))
+                )
+            )
+        )
+    "#;
+    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(), b"overwrite")).unwrap();
+    rt.tick();
+
+    let msg = inbox.try_recv().expect("host should overwrite pre-filled memory");
+    assert_eq!(msg.0, b"overwrite", "host should write fresh data over 0xFF");
+}
+
+// ── Engine clone shares same underlying engine ──────────────────────────────
+
+#[test]
+fn engine_clone_is_same_engine() {
+    let engine1 = SharedEngine::new().unwrap();
+    let engine2 = engine1.clone();
+
+    // Both should produce working actors
+    let actor1 = WasmActorBuilder::new(engine1, guest_wasm("echo")).build().unwrap();
+    let actor2 = WasmActorBuilder::new(engine2, guest_wasm("echo")).build().unwrap();
+
+    let rt = Runtime::new(RuntimeConfig::default());
+    let inbox = rt.new_inbox::<ByteMessage>().unwrap();
+    let a1 = rt.spawn(actor1).unwrap();
+    let a2 = rt.spawn(actor2).unwrap();
+
+    rt.send_to(a1, framed_msg(inbox.addr(), b"clone1")).unwrap();
+    rt.send_to(a2, framed_msg(inbox.addr(), b"clone2")).unwrap();
+    rt.tick();
+
+    let mut msgs: Vec<Vec<u8>> = Vec::new();
+    while let Some(msg) = inbox.try_recv() {
+        msgs.push(msg.0);
+    }
+    msgs.sort();
+    assert_eq!(msgs, vec![b"clone1".to_vec(), b"clone2".to_vec()]);
+}
+
+// ── Guest with i64 operations in handle ─────────────────────────────────────
+
+#[test]
+fn handle_uses_i64_operations() {
+    // Guest performs i64 arithmetic and stores result as i32.
+    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)
+                ;; Compute 1000000000 * 3 = 3000000000 (fits in i64 but not i32)
+                ;; Wrap to i32: 3000000000 mod 2^32 = 3000000000 (fits as u32)
+                ;; As i32: -1294967296
+                ;; Store low byte: 3000000000 & 0xFF = 0x00
+                ;; Actually let's just do something simpler: 100 + 200 = 300 → wrap i32
+                (i32.store8 (i32.const 200)
+                    (i32.wrap_i64
+                        (i64.add (i64.const 100) (i64.const 155))
+                    )
+                )
+                (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(), b"i64")).unwrap();
+    rt.tick();
+
+    let msg = inbox.try_recv().unwrap();
+    assert_eq!(msg.0[0], 255u8, "100 + 155 = 255");
+}
+
+// ── 200 actors from same engine all process one message ─────────────────────
+
+#[test]
+fn two_hundred_actors_from_same_engine() {
+    let engine = SharedEngine::new().unwrap();
+    let rt = Runtime::new(RuntimeConfig::default());
+    let inbox = rt.new_inbox::<ByteMessage>().unwrap();
+
+    let mut addrs = Vec::new();
+    for _ in 0..200 {
+        let actor = WasmActorBuilder::new(engine.clone(), guest_wasm("echo"))
+            .build()
+            .unwrap();
+        addrs.push(rt.spawn(actor).unwrap());
+    }
+
+    for (i, addr) in addrs.iter().enumerate() {
+        rt.send_to(*addr, framed_msg(inbox.addr(), &[(i & 0xFF) as u8])).unwrap();
+    }
+    rt.tick();
+
+    let mut count = 0;
+    while let Some(_) = inbox.try_recv() {
+        count += 1;
+    }
+    assert_eq!(count, 200, "all 200 actors should echo");
+}