src: fill in more details of the coroutine impl

Author: jasnell

src/coro/uv_awaitable.h

@@ -92,6 +92,11 @@ class UvFsAwaitable {
   // Access the raw request (useful before cleanup for stat, readdir, etc.)
   const uv_fs_t& req() const { return req_; }
 
+  // Returns a pointer to the underlying uv_req_t for cancellation support.
+  // Used by TrackedAwaitable to register with the request counter and
+  // cancellation infrastructure.
+  uv_req_t* cancelable_req() { return reinterpret_cast<uv_req_t*>(&req_); }
+
  private:
   static void OnComplete(uv_fs_t* req) {
     auto* self = static_cast<UvFsAwaitable*>(req->data);
@@ -196,6 +201,8 @@ class UvFsStatAwaitable {
     return r;
   }
 
+  uv_req_t* cancelable_req() { return reinterpret_cast<uv_req_t*>(&req_); }
+
  private:
   static void OnComplete(uv_fs_t* req) {
     auto* self = static_cast<UvFsStatAwaitable*>(req->data);
@@ -258,6 +265,8 @@ class UvWorkAwaitable {
   // Returns 0 on success, UV_ECANCELED if cancelled, or negative error.
   int await_resume() noexcept { return status_; }
 
+  uv_req_t* cancelable_req() { return reinterpret_cast<uv_req_t*>(&req_); }
+
  private:
   static void OnWork(uv_work_t* req) {
     auto* self = static_cast<UvWorkAwaitable*>(req->data);
@@ -331,6 +340,8 @@ class UvGetAddrInfoAwaitable {
 
   AddrInfoResult await_resume() noexcept { return {status_, addrinfo_}; }
 
+  uv_req_t* cancelable_req() { return reinterpret_cast<uv_req_t*>(&req_); }
+
  private:
   static void OnComplete(uv_getaddrinfo_t* req,
                          int status,

src/coro/uv_promise.h

@@ -16,13 +16,14 @@ namespace coro {
 // on_resume() already provides a HandleScope and will drain microtasks
 // and nextTick on close (in on_suspend / final_suspend).
 //
-// When used inside an untracked UvTask (no InternalCallbackScope),
-// these create their own HandleScope.
+// These guard against calling V8 APIs when the environment is shutting
+// down (can_call_into_js() is false).
 // ---------------------------------------------------------------------------
 
 inline void ResolvePromise(Environment* env,
                            v8::Global<v8::Promise::Resolver>& resolver,
                            v8::Local<v8::Value> value) {
+  if (!env->can_call_into_js()) return;
   v8::HandleScope scope(env->isolate());
   auto local = resolver.Get(env->isolate());
   USE(local->Resolve(env->context(), value));
@@ -39,6 +40,7 @@ inline void RejectPromiseWithUVError(
     int uv_err,
     const char* syscall,
     const char* path = nullptr) {
+  if (!env->can_call_into_js()) return;
   v8::HandleScope scope(env->isolate());
   auto local = resolver.Get(env->isolate());
   v8::Local<v8::Value> exception =
@@ -49,11 +51,6 @@ inline void RejectPromiseWithUVError(
 // ---------------------------------------------------------------------------
 // MakePromise — Creates a v8::Promise::Resolver, sets the return value
 // on `args`, and returns a Global handle for use in the coroutine.
-//
-// Usage from a binding function:
-//   auto resolver = MakePromise(env, args);
-//   auto task = my_coroutine(env, std::move(resolver), ...);
-//   task.Start();
 // ---------------------------------------------------------------------------
 
 inline v8::Global<v8::Promise::Resolver> MakePromise(