fix: open a window on Windows — WebView2 had nowhere to write its data

[Dale-Black]

Fixes #55.

What users saw

The Windows app started and did nothing: no window, no taskbar entry, and a process that never exited — so every click left another one behind. The reporter ended up with five SpaceStation.exe processes and, on the first launch after a reboot, one native dialog:

Microsoft Edge can't read and write to its data directory:
C:\Program Files\SpaceStation\SpaceStation.exe.WebView2\EBWebView

Why

WebView2 defaults its user-data folder to <exe>.WebView2 — beside the binary. Our MSI installs into %ProgramFiles%\SpaceStation, and deno desktop hard-codes ProgramFiles64Folder with no per-user install option, so on a standard account that path is read-only. Creating the WebView2 environment failed, the window was never created, and nothing in the shell treated that as fatal. Microsoft documents exactly this case: an unpackaged app in a protected install directory must name its own user-data folder.

The fix

desktop/webview2.ts points WEBVIEW2_USER_DATA_FOLDER at %LOCALAPPDATA%\SpaceStation\WebView2 before the first window exists. That reaches the loader because our code runs inside the webview host process — the app executable IS the laufey_webview host, which loads the Deno runtime and only then runs main.ts, while the WebView2 environment is created later on the first BrowserWindow. Verified by finding the WEBVIEW2_USER_DATA_FOLDER literal and GetEnvironmentVariableW in the shipped laufey_webview.exe, and by tracing the startup order on a real bundle.

Why CI never caught it

desktop/smoke.ts is headless by design — "everything except the window". The window layer had never once been executed in CI, on any OS. The .msi was built, uploaded and attached to releases without anything ever installing or running it (msiexec appeared nowhere in the repo).

So this PR also adds:

• desktop/window_smoke.ts — a headed companion that opens a real window and makes the webview prove it rendered by fetching a beacon URL. Runs on macOS and Windows in the test job. (Linux is deliberately excluded: the runner has no display or WebKitGTK stack, and a check that is allowed to fail is how this stayed invisible.)
• An install-and-launch job — installs the .msi it just built to the real Program Files location and launches it. GitHub's Windows runners are administrators with UAC disabled, so Program Files is writable there and Reload browser after pluto restart is confusing #55 would not reproduce on its own; a naive test would go green against the very bug it exists to catch. The step therefore revokes its own write access to the install directory first, then asserts the profile landed under LOCALAPPDATA and that nothing was written beside the binary.
• A liveness watchdog in main.ts — the runtime navigates the startup window to the shell's own server, so a healthy webview fetches a page within seconds. If nothing ever arrives, the shell now says why and exits non-zero instead of idling forever behind Deno.serve. That is what produced the pile of invisible processes.

Two smaller Windows bugs found along the way

• home_dir() preferred HOME over USERPROFILE. Git Bash/MSYS set HOME to somewhere Julia's homedir() never looks, and the two must agree — the server writes its connection file under homedir() and boot.ts reads the access secret back out of it.
• juliaup_info() split JULIA_DEPOT_PATH on ":", which severs the drive letter on Windows and turned C:\Users\me\.julia into C.

build:win now passes --icon: deno desktop decodes desktop.app.icons.macos (.icns) even when targeting Windows and fails the build, so that task was broken. A .ico is added and declared, though deno 2.9.5 embeds no Windows icon yet.

Known, not fixed here

Every build declares the same installer identity (ProductVersion 1.0.0, fixed ProductCode, no Upgrade table), so Windows can skip the upgrade and leave the old app in place. The release notes now tell Windows users to uninstall first; stamping real per-release identity is follow-up work.

Try this Pull Request!

Open Julia and type:

julia> import Pkg
julia> Pkg.activate(temp=true)
julia> Pkg.add(url="https://github.com/GroupTherapyOrg/SpaceStation.jl", rev="fix/windows-webview2-data-dir")
julia> using Pluto

[Dale-Black]

Opened against the wrong repository by mistake — this targets the GroupTherapyOrg/SpaceStation.jl fork, not Pluto.jl. Closing; sorry for the noise.