fix(desktop): run Windows servers without console windows

[crazy-daddy]

Summary

On Windows, clicking the Karma desktop icon leaves two console windows open (one for the API, one for the frontend). This PR starts the servers without them, on every install path.

Root cause: spawn_detached uses CREATE_NO_WINDOW | DETACHED_PROCESS. Per the CreateProcess flags docs, CREATE_NO_WINDOW is ignored when combined with DETACHED_PROCESS. The detached server has no console, so its own console children (uvicorn.exe → python.exe, npm.cmd → cmd.exe → node.exe) each allocate a new, visible console window.

Fix: spawn with CREATE_NO_WINDOW | CREATE_NEW_PROCESS_GROUP instead. The server gets a hidden console that its children inherit, and it still outlives the launcher. This matches the existing intent ("never flash a window"), so it is the only behavior: no flag, no opt-in.

Changes

• core.spawn_detached: Windows creation flags are now CREATE_NO_WINDOW | CREATE_NEW_PROCESS_GROUP (one line, plus a comment on why DETACHED_PROCESS can't be used).
• Tests: test_spawn_detached_hides_console asserts both flags are set and DETACHED_PROCESS is not; test_notify_opens_no_console_window asserts the balloon passes CREATE_NO_WINDOW.
• launcher.notify: the cold-start "Starting servers" balloon ran powershell -WindowStyle Hidden without CREATE_NO_WINDOW. Under pythonw the launcher has no console, so PowerShell got a new, visible one (a Windows Terminal window on Windows 11) before the hidden style applied. Found while retesting the cold start; it has been there since feat(desktop): one-click launcher + autostart for macOS and Windows #94. Now passes CREATE_NO_WINDOW, with a test.
• Installer, shortcuts and the dashboard's Settings → Desktop App install are unchanged. The servers all go through spawn_detached, so every install path gets the fix.
• main (after Make local Karma fast: normal-priority autostart, git cache, subagent parse cache, production frontend #112) merged in; the conflict in spawn_detached is resolved onto the new _popen helper. run_logged and stop_process_tree (taskkill /T) are unaffected.

Component

• API (FastAPI backend)
• Frontend (SvelteKit dashboard)
• Captain Hook (hook models)
• Hook Scripts
• Documentation
• CI / Build
• Desktop launcher (scripts/karma_desktop, scripts/install_karma_app.py)

Type

• Feature (new functionality)
• Bug fix
• Refactor (no behavior change)
• Performance improvement
• Documentation
• Tests

Testing

• scripts/tests (83 passed, 17 skipped as other-OS) and api/tests/test_desktop_app_guard.py (12 passed, 2 skipped) pass on Windows
• ruff check and ruff format --check clean on scripts/ and the endpoint, as in the desktop-launcher workflow
• Manually tested these flags on Windows 11: no console windows; servers keep running after the launcher exits, and a second click while running only reopens the dashboard
• Checked on Windows 11 by recording every console window that opened: a cold start from the icon opened one (the balloon's PowerShell), and with this fix it opens none
• Autostart toggled on in the dashboard's Settings → Desktop App: the Startup entry carries --no-open --quiet and no extra flag. Running it the way Windows does at login, with both servers stopped, brought both back with no console windows and no browser window
• Not tested on macOS (no change there: the flags are Windows-only)

Related Issues

None filed. Companion PR: #109 (open the dashboard in the Windows default browser). Both touch launcher.py and its tests in different places; they merge together without conflicts in either order.

[JayantDevkar]

Inline context for reviewers, one note per change area.

[JayantDevkar]

Good find on the CREATE_NO_WINDOW + DETACHED_PROCESS interaction, that explains the two consoles people have hit.

You offered to flip the default or drop the flag, and I'd take the second option. The existing comment says "never flash a window", so windowless was always the intent, and I can't think of a reason someone would opt back into the console windows. Making the new creation flags unconditional turns this into a small change in spawn_detached plus the two tests on the flags, and removes the --silent plumbing through the installer, the shortcut arguments and the launcher. It also avoids a gap in the current version: the dashboard's own Settings → Desktop App install doesn't know about the flag, so toggling autostart there would rewrite the shortcut without --silent.

While you're in there, README line 291 still says no console window flashes on Windows; after this change it'll be true again, so it can stay.

I'll approve the CI run so the Windows job picks up your tests.

[crazy-daddy]

Thanks! Dropped --silent as suggested, so the hidden-console flags are now the only behavior (bbadef8). I also merged in main after #112, which conflicted with spawn_detached (3743a0e).
While retesting the cold start I found one more flash: the “Starting servers” balloon ran PowerShell without CREATE_NO_WINDOW. It was there before this PR, but it’s the same bug, so the fix is in here too (b30f66e).
Retested on Windows 11, recording every console window that opened: icon cold start, icon while running, and autostart toggled in Settings → Desktop App and then run as Windows does at login. No console windows in any of them.

Title and description are updated.