Phase 2: create a real Node-API env via hermes_napi_create_env

Replace the `env = nullptr` stub in CxxNodeApiHostModule with a real
Node-API environment: cast the JSI runtime to `IHermes`, read the
underlying `vm::Runtime*` via `getVMRuntimeUnsafe()`, and create the env
with `hermes_napi_create_env(vm, nullptr)`. The env is owned by the
runtime and cached on the module (shared across all addons).

This flips the Phase 1 baseline abort (`assert(status == napi_ok)` right
after `napi_create_object(env=nullptr, …)`) green: with
`MOCHA_REMOTE_CONTEXT=allTests` the iOS-sim suite now reports 14 passing
(node-addon-examples getting-started incl. the Rust ferric addon,
buffers, async, and a js-native-api node-test).

Linking note: the RN `hermesvm` framework force-loads `hermesNapi`, and
the public `hermes_napi_*` entry points are exported from it as long as
Hermes is built from a checkout that includes facebook/hermes #2044
("Export public hermes_napi entry points with NAPI macros") — which the
pinned SHA (0ae42446) already contains. No pod-side linker surgery or
source patching is required; just ensure the vendored checkout is
actually at the pinned SHA (a stale pre-#2044 checkout is what stripped
the symbol during bring-up).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: kraenhansen

packages/host/cpp/CxxNodeApiHostModule.cpp

@@ -2,8 +2,19 @@
 #include "Logger.hpp"
 #include "RuntimeNodeApiAsync.hpp"
 
+#include <jsi/hermes-interfaces.h>
+
 using namespace facebook;
 
+// Declared by the vendored Hermes in API/napi/hermes_napi.h. We forward declare
+// it here (rather than including that header) to avoid pulling in Hermes' own
+// node_api.h alongside the weak-node-api copy already included transitively.
+// Only the mangled name matters for linking, so passing host as nullptr is
+// enough — async work / thread-safe functions will return failure until a
+// host integration is wired up (Phase 3).
+struct hermes_napi_host;
+napi_env hermes_napi_create_env(void *hermes_runtime, hermes_napi_host *host);
+
 namespace callstack::react_native_node_api {
 
 CxxNodeApiHostModule::CxxNodeApiHostModule(
@@ -108,8 +119,25 @@ bool CxxNodeApiHostModule::initializeNodeModule(jsi::Runtime &rt,
   // TODO: Read the version from the addon
   // @see
   // https://github.com/callstackincubator/react-native-node-api/issues/4
-  // TODO: Phase 2-3 will replace this with hermes_napi_create_env
-  napi_env env = nullptr;
+
+  // Lazily create the Node-API environment backing this runtime. Hermes binds
+  // an env to its low-level VM runtime, which we reach through the (unstable)
+  // IHermes JSI interface. The env is owned by the runtime and shared across
+  // all addons, so we create it once and cache it.
+  if (env_ == nullptr) {
+    // Fully qualified: `using namespace facebook` makes a bare `hermes`
+    // ambiguous with the top-level `::hermes` (VM) namespace pulled in via
+    // <jsi/hermes-interfaces.h>.
+    auto *hermes = facebook::jsi::castInterface<facebook::hermes::IHermes>(&rt);
+    if (hermes == nullptr) {
+      log_debug("NapiHost: JSI runtime is not castable to IHermes; cannot "
+                "create a Node-API environment");
+      abort();
+    }
+    env_ = hermes_napi_create_env(hermes->getVMRuntimeUnsafe(), nullptr);
+    assert(env_ != nullptr);
+  }
+  napi_env env = env_;
 
   // Create the "exports" object
   napi_value exports;

packages/host/cpp/CxxNodeApiHostModule.hpp

@@ -30,6 +30,11 @@ class JSI_EXPORT CxxNodeApiHostModule : public facebook::react::TurboModule {
   std::unordered_map<std::string, NodeAddon> nodeAddons_;
   std::shared_ptr<facebook::react::CallInvoker> callInvoker_;
 
+  // The Node-API environment backing every addon loaded into this runtime.
+  // Created lazily on first use from the underlying Hermes VM runtime and
+  // shared across all addons (Node-API expects a single env per realm).
+  napi_env env_ = nullptr;
+
   using LoaderPolicy = PosixLoader; // FIXME: HACK: This is temporary workaround
                                     // for my lazyness (work on iOS and Android)