Add a setting for sending a notification on BEL

[carlos-zamora]

Summary of the Pull Request

Targets #20010

Adds another bellStyle flag option. This sends a windows toast notification to the user when a BEL is encountered

• Closes Windows Notification on Bell #18605
• Documentation updated

Heavily based on #19936
Co-authored by @zadjii-msft

[carlos-zamora]

The only change I made was I changed the settings UI string from "Send notification" to "Desktop notification"

Separately, I noticed that the default here is audible. A few related questions:

1. Any interest in adding "desktop notification" as the default too?
   • I'm leaning "no". Particularly because I know that I hit a BEL in WSL every time I backspace into the prompt and that would be annoying haha. Wanted to poll for opinions though.
2. visual in the JSON maps to window + taskbar. Should notification be added here too?
   • Kinda torn. It is visual, but it's also kinda outside the frame of the terminal, so I feel like it's a completely different thing.

I also played around with it and I noticed this:

1. open WSL - Ubuntu terminal
2. create BEL (backspace into prompt)
3. Get notification

4. Click notification 5. Get a new Terminal window!

I double checked and we are hitting this code in AppCommandlineArgs::ParseArgs() as expected:

terminal/src/cascadia/TerminalApp/AppCommandlineArgs.cpp

Lines 1071 to 1078 in 4357c17

	// When a toast notification is clicked, Windows may launch a new instance
	// with "__fromToast" as the argument. This is a no-op sentinel — the
	// in-process Activated handler on the toast already handled activation.
	// See DesktopNotification.cpp for more details.
	if (args.size() == 2 && args[1] == L"__fromToast")
	{
	return 0;
	}

Shouldn't we refocus the tab/pane that sent the notification instead? @zadjii-msft thoughts?

[lhecker]

Would this send a toast every 3s if I send a bell every 3s? Is it a concern to us to throttle this even further? (I'd probably lean to "no", personally.)

[carlos-zamora]

We have a throttle in DesktopNotification here:

terminal/src/cascadia/TerminalApp/DesktopNotification.cpp

Lines 20 to 34 in 9df166e

	bool DesktopNotification::ShouldSendNotification()
	{
	FILETIME ft{};
	GetSystemTimeAsFileTime(&ft);
	const auto now = (static_cast<int64_t>(ft.dwHighDateTime) << 32) | ft.dwLowDateTime;
	auto last = _lastNotificationTime.load(std::memory_order_relaxed);
	if (now - last < MinNotificationIntervalTicks)
	{
	return false;
	}
	// Attempt to update; if another thread beat us, that's fine — we'll skip this one.
	return _lastNotificationTime.compare_exchange_strong(last, now, std::memory_order_relaxed);
	}

It's currently set to 5 seconds:

terminal/src/cascadia/TerminalApp/DesktopNotification.h

Line 36 in 9df166e

static constexpr int64_t MinNotificationIntervalTicks = 50'000'000LL;

The flow is:
TabToastNotificationRequested --> TerminalPage::_SendDesktopNotification() --> DesktopNotification::SendNotification()

So I think the 5s throttle is good, but we can adjust it if we want.