[ammarahm-ed]

Every V8 nsr run on macOS aborts at exit with:

# Fatal error in v8::Context::Exit()
# Cannot exit non-entered context

It happens even for an empty script, after the script has finished. The Performance (v8) CI job runs the CLI, so it has failed on every PR into refactor, including #68 and #69.

Cause

1. ~Runtime keeps a NapiScope open around js_free_napi_env. NapiScope enters env->context(), which is a Local pointing straight into the env's own persistent slot. The header warns against resetting that slot while the Local is in use. Freeing the env destroys the slot, so when the scope closes, Context::Exit reads a dead handle and V8 aborts.
2. Fixing that exposed a second crash. The ES module cache keeps Global<Module>s per isolate in a thread-local map, and nothing released them. CleanupESModuleSystem exists but was never called, so the map was cleared at process exit, after the isolate was already disposed, and crashed.

Fix

• The env is freed in its own scope, after globalScope_ is closed. That scope enters a copy of the context owned by its own HandleScope, so the env's finalizers still run inside the context. Non-V8 engines are unchanged.
• js_free_runtime calls CleanupESModuleSystem before disposing the isolate.

Testing

• Empty and small scripts: exit 0. Before the fix they exited with 133.
• Objective-C dispatch benchmark: exits 0 in 3 of 3 runs, with all results reported.
• macOS V8 runtime suite: 720 specs, 0 failures.

This PR's own Performance (v8) check will still fail: it builds its baseline from refactor, which still has the bug. Once this is merged, the baseline is fixed for every later PR, including #117.

🤖 Generated with Claude Code

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