Add API flags for creating & opening persistent sessions

[OneBlue]

Summary of the Pull Request

This will be needed for the CLI to open & maintain its session across invocations

PR Checklist

• Closes: Link to issue #xxx
• Communication: I've discussed this with core contributors already. If work hasn't been agreed, this work might be rejected
• Tests: Added/updated if needed and all pass
• Localization: All end user facing strings can be localized
• Dev docs: Added/updated if needed
• Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

[OneBlue]

@kevpar: This is one of the API changes that I mentioned. This will allow a caller to specify that a session should outlive its last COM client reference.

The WSLASessionFlagsOpenExisting flag will make it easy for the CLI to have a "create-or-open" logic when setting up its COM session

[benhillis]

For persistent sessions what are you thinking for lifetime of the VM? We likely want to clean it up after some period of inactivity.

[OneBlue]

For persistent sessions what are you thinking for lifetime of the VM? We likely want to clean it up after some period of inactivity.

This is something that we still need to design. Most likely we're going to need some form of configuration file for the container CLI, and in it we can have an inactivity timeout, similar to what we do in WSL

[Copilot]

Pull request overview

This PR adds API flags for creating and opening persistent WSL sessions that can outlive their COM reference lifetime. The main purpose is to support the CLI's ability to maintain sessions across invocations by introducing WSLASessionFlagsPersistent and WSLASessionFlagsOpenExisting flags.

Changes:

• Added session flag enums (WSLASessionFlagsPersistent, WSLASessionFlagsOpenExisting) to control session lifecycle behavior
• Removed the deprecated IWSLAVirtualMachine interface and migrated its functionality to IWSLASession
• Replaced Shutdown() with Terminate() and changed WSLAVirtualMachine from a COM object to an internal std::optional member
• Added comprehensive test coverage for persistent session behavior including creation, reopening, and termination

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
src/windows/wslaservice/inc/wslaservice.idl	Added WSLASessionFlags enum, updated CreateSession signature, removed IWSLAVirtualMachine interface, renamed Shutdown to Terminate, added testing methods to IWSLASession
src/windows/wslaservice/exe/WSLAUserSession.h	Added m_persistentSessions vector to store strong references, updated CreateSession signature, added logic to remove terminated persistent sessions
src/windows/wslaservice/exe/WSLAUserSession.cpp	Implemented session lookup by name with OpenExisting flag support, added persistent session reference management
src/windows/wslaservice/exe/WSLASession.h	Changed m_virtualMachine from ComPtr to std::optional, renamed Shutdown to Terminate, added Terminated() method, moved VM methods from IWSLAVirtualMachine
src/windows/wslaservice/exe/WSLASession.cpp	Refactored Terminate() to be callable explicitly, moved VM operation wrappers from deleted interface, changed VM initialization to use emplace
src/windows/wslaservice/exe/WSLAVirtualMachine.h	Removed COM interface inheritance, changed methods from HRESULT-returning to void/exception-throwing
src/windows/wslaservice/exe/WSLAVirtualMachine.cpp	Removed WaitPid, Shutdown methods, changed MapPort/Unmount/Signal to throw exceptions instead of returning HRESULT
src/windows/wslaservice/exe/WSLAContainer.cpp	Updated MapPort calls to use try/catch instead of LOG_IF_FAILED since it now throws
src/windows/wslaservice/exe/WSLAProcessControl.cpp	Updated Signal call to handle void return type
src/windows/common/WslClient.cpp	Updated CreateSession call to pass WSLASessionFlagsNone, removed IWSLAVirtualMachine usage
test/windows/WSLATests.cpp	Updated all tests to use new API, replaced Shutdown with session.reset() or Terminate(), added PersistentSession test with comprehensive coverage, removed test for process creation after VM termination
src/shared/inc/lxinitshared.h	Removed WSLA_WAITPID, WSLA_WAITPID_RESULT, and WSLA_SHUTDOWN message structures
src/linux/init/WSLAInit.cpp	Removed HandleMessageImpl for WSLA_WAITPID, removed WSLA_WAITPID from HandleMessage template list
msipackage/package.wix.in	Removed registry entries for WSLAVirtualMachine and IWSLAVirtualMachine COM classes