No stray windows on Windows, steadier commands and safer engine stops

Windows

• No more empty console windows. The desktop app, its engine and the commands an agent runs no longer flash or leave behind black terminal windows. Checked on a real Windows desktop: 3.9.0 opened 40 windows during a session, this release opens none.
• An agent can no longer open a console window by accident. When it tries start, cmd /c start or Start-Process for a program that would open its own window, Empryo stops it, says why and suggests running it directly or in the background instead. Opening folders, documents, web pages and windowed apps still works.

Commands

• Long-running commands keep their output without slowing down. Output from a chatty command is kept in rolling pieces, so the agent always sees the latest lines and the beginning, and the log never grows without limit.
• A slow command is no longer killed while it is still working. The watchdog waits for the command instead of cutting it off.
• Stopping a turn before a build or test starts means it never starts.

Engines

• Force-stopping an engine stops the one you picked. /engines now names an engine by its process and generation, so if the list changes before you confirm, the force stop is refused instead of hitting a different engine.