fix(windows): prevent helper process console flashes

[YuYigeng]

What does this PR do?

Prevents visible console flashes from the two remaining helper-process spawn paths on Windows installations created by uv.

The venv python.exe launcher re-execs the base console interpreter, so CREATE_NO_WINDOW on the launcher cannot suppress the second conhost. This change reuses the existing uv-aware interpreter resolution to launch both the TUI slash worker and the gateway restart watcher with the base pythonw.exe. It also supplies the VIRTUAL_ENV and PYTHONPATH overlay required by the base interpreter, while preserving profile-specific HERMES_HOME and safe fallback behavior.

Related Issue

Fixes #68457

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✅ Tests (adding or improving test coverage)

Changes Made

• Added a private reusable windowless-Python spawn specification in hermes_cli/gateway_windows.py.
• Updated tui_gateway/server.py so _SlashWorker launches uv environments through the base pythonw.exe and retains its profile environment.
• Updated hermes_cli/gateway.py so the restart watcher itself, not only the gateway it later respawns, uses pythonw.exe with the required cwd and environment.
• Added behavioral coverage for real uv pyvenv.cfg resolution, profile propagation, non-Windows behavior, and resolution-failure fallback.

Validation

After rebasing onto current main (including #56747's additional Windows hide-flag paths and tests):

• HERMES_PYTHON=/path/to/python scripts/run_tests.sh tests/hermes_cli/test_gateway.py tests/hermes_cli/test_gateway_windows.py tests/gateway/test_restart_drain.py tests/test_tui_gateway_server.py tests/test_windows_subprocess_no_window_flags.py tests/tui_gateway/test_slash_worker_profile_home.py — 589 passed
• ruff check hermes_cli/gateway.py hermes_cli/gateway_windows.py tui_gateway/server.py tests/hermes_cli/test_gateway.py tests/test_windows_subprocess_no_window_flags.py — passed
• python scripts/check-windows-footguns.py --diff upstream/main — passed across all five changed files
• git diff --check upstream/main...HEAD — passed

The spawn-path tests construct a real uv-style pyvenv.cfg, base pythonw.exe, and venv site-packages so the resolver is exercised end to end. Non-Windows behavior and resolution failure retain the original sys.executable fallback. The upstream #56747 regression coverage for the six other GUI-reachable spawn sites remains intact.

I also attempted the full suite. It reached 37% before I stopped it after unrelated host/environment failures, including a Linux systemd abstract-socket test on macOS and Discord fixture URLs resolving to an SSRF-blocked reserved address. All suites covering the changed paths passed.

Checklist

• Read the contribution guidance
• Conventional commit and GitHub-linked author identity
• Searched for duplicate PRs
• Only scoped files are changed
• Added behavioral regression coverage
• Considered Windows and non-Windows behavior
• No public API or configuration keys added

Screenshots / Logs

Not applicable: this is process-launch behavior covered by subprocess-spawn assertions and real uv-layout resolver fixtures.

[teknium1]

Closing as superseded by PR #70205 (merged as 0dbf639), which fixes this class in the opposite direction.

This PR rewrites the restart watcher to GUI-subsystem pythonw.exe — but main just removed all pythonw daemon launches deliberately: a console-less parent is what causes the per-descendant console flashes (#54220/#56747), since every console-subsystem child must allocate its own visible console. The watcher now runs console python under CREATE_NO_WINDOW (it owns one hidden console its children inherit), and the slash_worker spawn already carries windows_hide_flags() on main.

If you still see a flash on these legs on current main, please re-open with the flashing process name — that would be a leg the parent-console fix doesn't cover. Thanks for the detailed spawn-chain analysis.