Fix executor mutex race condition and memory leak

[ghostwriternr]

Summary

Fixes race condition in getExecutorLock() where concurrent calls could create duplicate mutex instances, defeating serialization. Also fixes memory leak where executor mutexes weren't cleaned up on process exit.

Test plan

• E2E tests pass locally
• Improved isolation test now verifies state across 12 contexts using globalThis

[changeset-bot]

🦋 Changeset detected

Latest commit: 9ceaa8e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@cloudflare/sandbox	Patch

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[pkg-pr-new]

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npm i https://pkg.pr.new/cloudflare/sandbox-sdk/@cloudflare/sandbox@258

commit: 9ceaa8e

[github-actions]

🐳 Docker Image Published

FROM cloudflare/sandbox:0.0.0-pr-258-2e2af2d

Version: 0.0.0-pr-258-2e2af2d

You can use this Docker image with the preview package from this PR.

[ghostwriternr]

@claude can you fix the issues raised in the code review comments

[claude]

Claude finished @ghostwriternr's task —— View job

---

Fixed Code Review Issues ✓

All three issues from the code review have been fixed and pushed:

Changes Made

1. Critical Issue Version Packages #1 - Missing mutex cleanup in cleanupIdleProcesses() (line 675)

   • Added this.executorLocks.delete(process.id) after killing idle processes
   • Prevents memory leak when idle executors are cleaned up

2. Critical Issue Version Packages #2 - Missing mutex cleanup in shutdown() (line 763)

   • Added this.executorLocks.clear() at the end of shutdown
   • Ensures all executor locks are cleaned up on shutdown

3. Minor Issue - Misleading comment in releaseExecutorForContext() (line 563)

   • Changed comment from "Remove exit handler to prevent memory leak" to "Remove exit handler since we're doing manual cleanup"
   • Better reflects the actual purpose of removing the handler

Verification

• ✅ TypeScript compilation passes
• ✅ All unit tests pass (292 tests in sandbox package, 427 tests in container package)
• ✅ Changes committed and pushed to interpreter-fixes-cleanup branch

The memory leak fixes are now complete. The mutex cleanup now happens in all process termination paths:

• Unexpected process exit (via exit handler)
• Manual context release
• Idle process cleanup
• System shutdown

--- | Branch: interpreter-fixes-cleanup