[Aschenbath]

Closes #36501

On Windows, console.log and console.error from a deno desktop --hmr app never reached the terminal.

The laufey backend (laufey_webview.exe) is a GUI-subsystem executable. When deno desktop --hmr starts it from a console, Windows gives it no console and no standard handles: GetStdHandle(STD_OUTPUT_HANDLE) and GetStdHandle(STD_ERROR_HANDLE) both return null in the backend, so everything the runtime writes is dropped. When deno's output is redirected to a file or pipe, the handles are passed explicitly and the output shows up, which is why this only happens in a real console.

At startup, rt_desktop now checks whether DENO_DESKTOP_HMR is set and the process has no console. If so, it attaches to the parent's console (AttachConsole(ATTACH_PARENT_PROCESS)), and points stdout and stderr at CONOUT$ where they're still null. Handles the parent passed explicitly, such as a pipe or a file, are kept. DENO_DESKTOP_HMR is only set for development runs, so an app started normally, e.g. from Explorer, still runs without a console.

Testing

Windows 11, main.ts containing console.log("hello-from-desktop"); console.error("err-from-desktop");, deno desktop --hmr main.ts with the webview backend:

	released 2.9.8	this branch (deno + denort.dll built locally)
real console	neither line appears	both lines appear
output redirected to a file	both lines	both lines

To read the real console, I started deno in a new console window (CREATE_NEW_CONSOLE), attached to that console and read its screen buffer. A temporary diagnostic in this function confirmed that both standard handles are null in the backend before this change.

cargo clippy -p denort_desktop -- -D warnings, cargo fmt --check and dprint are clean.

Not covered: stdin is left as it was, and I haven't checked the CEF backend.

AI disclosure

This PR was written primarily by Claude Code (Claude Opus 5.5), including the change, the investigation and this description.

🤖 Generated with Claude Code

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}