test(tools): regression test for Windows creationflags double-pass (#29651)

[Snehal707]

Summary

Add a regression test ensuring LocalEnvironment._run_bash passes creationflags only once on Windows.

Related to #29651

What was happening

On Windows, subprocess.Popen() in LocalEnvironment._run_bash received creationflags twice: once as an explicit keyword (CREATE_NO_WINDOW) and again via **_popen_kwargs (windows_hide_flags()). That raised got multiple values for keyword argument 'creationflags', breaking terminal() and write_file() on the local backend.

What changed

• New unit test: tests/tools/test_local_popen_creationflags.py
• No production code changes; fix already landed in fix(windows): drop duplicate creationflags kwarg in LocalEnvironment run_bash #29059.

How to verify

1. pytest tests/tools/test_local_popen_creationflags.py -q (on Windows use --timeout-method=thread if needed)
2. On Windows with latest main: terminal(command="echo hello") and write_file(path="test.txt", content="test") should succeed.

Platforms tested

• Windows 11 (native), Python 3.11 venv

[alt-glitch]

Related to #29213 — both are test-only regression guards for the creationflags double-pass bug (already fixed by merged #29059). Different test files/approaches.

[teknium1]

Thanks for adding a focused regression guard. This automated hermes-sweeper review found that the reported Windows double-pass is already fixed on current main.

• tools/environments/local.py:1074-1087 supplies creationflags through _popen_kwargs and expands it once into subprocess.Popen(...); there is no explicit second creationflags= argument.
• Commit 05f02640e1f763afb7afdae4efe6b450016a908f is the direct fix, removing the duplicate explicit keyword from this call.
• The fix is included in release v2026.5.28.
• @alt-glitch's note correctly identifies this PR as a test-only guard for the behavior already repaired by merged PR fix(windows): drop duplicate creationflags kwarg in LocalEnvironment run_bash #29059.

Closing as implemented on main.