Introduce a launcher coordinator to reserve startup ownership and prevent duplicate host launches. Adds a NamedPipe-based IPC server/client (LauncherCoordinatorIpcServer/Client), coordinator messages/models, and PublicShellStatus/activation types for richer shell reporting. Enhances StartupAttemptRecord and StartupAttemptRegistry to track coordinator pid/pipe, heartbeat, reserved-before-host-start, and public IPC status, plus new reservation/heartbeat APIs and takeover logic. Wire coordinator into App and LauncherFlowCoordinator to attach secondary launchers, publish coordinator status, probe existing hosts, and include more detailed launch result details. Also adds unit tests and docs describing coordinator and startup visuals behavior.
Introduce a new LanMountainDesktop.Shared.IPC project implementing a public IPC host and client (LanMountainDesktopIpcClient, PublicIpcHostService), IPC constants and routed notify IDs, DTOs and DI helpers for registering public services. Update Plugin SDK to allow plugins to contribute public IPC services and registrations, add related descriptors/records and extension helpers. Migrate Launcher/App to use the new public IPC for startup/loading notifications and wiring (including TryConnect helper), switch LoadingStateReporter to use the external notification publisher, and add host-side public services (app info, shell control, plugin catalog). Include integration tests and spec/checklist/docs for the external IPC public API.
