(Issue)- unbounded memory growth during actors cycling.

[itsme-boii]

Summary:-
ActorContextShared::reset_runtime_state() in rivetkit-napi uses std::mem::forget to avoid a panic when dropping a napi::Ref on a Tokio worker thread (where no Node.js Env is available). This leaks one JS object reference slot per actor wake cycle. Over time in long-running processes with many actors cycling through sleep/wake, this is unbounded memory growth.

Problem:-
When an actor wakes from sleep, reset_runtime_state() is called to clear the previous JS state object. The napi::Ref type requires calling .unref(env) with a valid Node.js Env handle to properly release the reference. But reset_runtime_state() runs on a Tokio worker thread where no Env exists.

The current code uses std::mem::forget(old) to suppress the destructor. This avoids a debug_assert panic in napi-rs, but permanently leaks the underlying V8 reference slot.

The same pattern appears in the Drop impl for ActorContextShared.

File: rivetkit-typescript/packages/rivetkit-napi/src/actor_context.rs

if let Some(old) = self.runtime_state.lock().take() {
    std::mem::forget(old);
}

Impact:-

• Rivet Actors are designed to sleep and wake frequently. An actor that wakes 100 times leaks 100 JS reference slots.
• The leak is per-actor, per-wake. A deployment with thousands of actors cycling through sleep/wake accumulates leaked references without bound.
• The only relief is process restart.

[linear-code]

ACT-6418

[itsme-boii]

Fix:-
Install a lightweight ThreadsafeFunction (the "ref dropper") on ActorContextShared that accepts stale Ref values and calls .unref(env) on the JS thread where the Env is available.

• The dropper is lazily installed on first Env access (when runtime_state() or clear_runtime_state() is called).
• It is marked as a weak reference (tsfn.unref()) so it does not prevent Node.js shutdown.
• If the dropper is not installed (test contexts without a JS runtime), the code falls back to std::mem::forget with a warning log.

if let Some(old) = self.runtime_state.lock().take() {
    self.drop_ref_safely(old);
}

fn drop_ref_safely(&self, stale_ref: Ref<()>) {
    let dropper = self.ref_dropper.lock().clone();
    if let Some(dropper) = dropper {
        dropper.call(stale_ref, ThreadsafeFunctionCallMode::NonBlocking);
    } else {
        tracing::warn!("ref_dropper not installed, leaking napi::Ref (expected only in tests)");
        std::mem::forget(stale_ref);
    }
}