node-api: enter env context for async callbacks

[codebytere]

AsyncResource::CallbackScope has to be opened with the resource's environment context entered; InternalCallbackScope otherwise asserts that Environment::GetCurrent(isolate) is that environment. uvimpl::Work::AfterThreadPoolWork() and the thread-safe function's DispatchOne() and Finalize() opened it with only a HandleScope, while CallFinalizer() beside them enters context() first. With one Environment per isolate that never shows, since the loop runs with that context entered. With two Environments on one isolate sharing a loop, an addon's napi_async_work completion or thread-safe function call aborts the process whenever the other Environment's context is the current one when the loop gets to it:

#  Node.js[216]: node::InternalCallbackScope::InternalCallbackScope(...) at ../../src/api/callback.cc:108
#  Assertion failed: (Environment::GetCurrent(isolate)) == (env)

This enters the node-api env's context at those three sites, the same way the zlib and WebCrypto thread pool callbacks do. In Finalize() the scope covers only the finalizer call rather than the whole function: context() returns a handle onto the env's persistent, and MaybeDelete() at the end can drop the last reference and free the env, so a function-wide scope would exit through a dead handle (test_threadsafe_function_shutdown covers that).

The node-api env's own context is used rather than node_env()->context(); they are the same today since addons only load in the principal realm.

Tests: new cctest NodeApiTest.AsyncCallbacksEnterOwnContext creates two Environments on one isolate, queues async work and a thread-safe function call from an addon in the first with the second's context entered, runs the loop, and checks that the complete callback, call_js and the thread-safe function's finalizer each ran in the addon's context; it hits the assertion above on main and passes here. cctest, node-api, js-native-api and async-hooks suites pass.

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Disclosure: the code, test and this description were written by Claude Code, directed and reviewed by @codebytere.

[nodejs-github-bot]

Review requested:

• @nodejs/node-api

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.12%. Comparing base (03fb384) to head (bea5dfb).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65406      +/-   ##
==========================================
+ Coverage   90.10%   90.12%   +0.01%     
==========================================
  Files         752      752              
  Lines      252209   252212       +3     
  Branches    47454    47449       -5     
==========================================
+ Hits       227260   227302      +42     
+ Misses      16264    16209      -55     
- Partials     8685     8701      +16     

Files with missing lines	Coverage Δ
src/node_api.cc	75.33% <100.00%> (+0.09%)	⬆️

... and 39 files with indirect coverage changes

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