Implement PROC_THREAD_ATTRIBUTE_LIST for handle inheritance

[tgauth]

PR Summary

• utilize PROC_THREAD_ATTRIBUTE_LIST to make inherited handles explicit (STDIO + auxiliary handles)

PR Context

• prevent any future changes from implicitly adding inherited handles

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Replaces the implicit inherit-all-handles behavior of CreateProcess/CreateProcessAsUser calls in posix_spawn_internal with an explicit allow-list using PROC_THREAD_ATTRIBUTE_HANDLE_LIST, so only the intended stdio and auxiliary handles are inherited by spawned children.

Changes:

• Added build_inherit_handle_attr_list() helper that constructs and initializes a PROC_THREAD_ATTRIBUTE_LIST for a given handle set.
• Refactored spawn_child_internal() to accept a caller-owned STARTUPINFOEXW* instead of individual stdio handles + internal STARTUPINFOW.
• Updated posix_spawn_internal() to build the inherit list (stdio + aux fds), set EXTENDED_STARTUPINFO_PRESENT, and clean up the attribute list, with a fall-back to default inheritance if attribute-list setup fails.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 3 comments.

[tgauth]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).