Synchronize the loaded modules and global scope variables between two Runspaces

library.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFramework>netstandard2.0</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="PowerShellStandard.Library" Version="5.1.0" />
  </ItemGroup>

</Project>

RunspaceSynchronizer.cs

using System;
using System.Collections.Generic;
using System.Management.Automation;

public class RunspaceSynchronizer
{
    public static bool SourceActionEnabled = false;
    private static bool TargetActionEnabled = false;

    // 'moduleCache' keeps track of all modules imported in the source Runspace.
    // when there is a `Import-Module -Force`, the new module object would be a
    // different instance with different hashcode, so we can tell if there is a
    // force loading of an already loaded module.
    private static HashSet<PSModuleInfo> moduleCache = new HashSet<PSModuleInfo>();

    // 'variableCache' keeps all global scope variable names and their value type.
    // As long as the value type doesn't change, we don't need to update the variable
    // in the target Runspace, because all tab completion needs is the type information.
    private static Dictionary<string, Type> variableCache = new Dictionary<string, Type>(StringComparer.OrdinalIgnoreCase);

    public static List<PSModuleInfo> moduleToImport = new List<PSModuleInfo>();
    public static List<PSVariable> variablesToSet = new List<PSVariable>();

    private static EngineIntrinsics sourceEngineIntrinsics;
    private static EngineIntrinsics targetEngineIntrinsics;
    
    private static object syncObj = new object();
    private static bool sourceEventSubscribed = false;
    private static bool targetEventSubscribed = false;
    
    private static void CollectSourceRunspaceState(object sender, PSEventArgs args)
    {
        if (!SourceActionEnabled)
        {
            return;
        }

        try
        {
            // Maybe also track the latest history item id ($h = Get-History -Count 1; $h.Id)
            // to make sure we do the collection only if there was actually any input.

            var newOrChangedModules = new List<PSModuleInfo>();
            var newOrChangedVars = new List<PSVariable>();

            var results = sourceEngineIntrinsics.InvokeCommand.InvokeScript("Get-Module");
            foreach (var res in results)
            {
                var module = (PSModuleInfo) res.BaseObject;
                if (moduleCache.Add(module))
                {
                    newOrChangedModules.Add(module);
                }
            }

            // Process variables to get those that need to be updated.
            // - first filter out the built-in variables.
            // - check against the existing variable cache, if the value type of a variable name remains the same,
            //   then no need to update the variable.
            // - finally get a dictionary of new/updated variables.

            if (newOrChangedModules.Count == 0 && newOrChangedVars.Count == 0)
            {
                return;
            }

            lock (syncObj)
            {
                moduleToImport.AddRange(newOrChangedModules);
                variablesToSet.AddRange(newOrChangedVars);
            }

            // Enable the action in target Runspace
            TargetActionEnabled = true;
        } catch (Exception ex) {
            Console.WriteLine(ex.Message);
            Console.WriteLine(ex.StackTrace); 
        }

        SourceActionEnabled = false;
    }

    private static void UpdateTargetRunspaceState(object sender, PSEventArgs args)
    {
        if (!TargetActionEnabled)
        {
            return;
        }

        List<PSModuleInfo> newOrChangedModules;
        List<PSVariable> newOrChangedVars;

        lock (syncObj)
        {
            newOrChangedModules = new List<PSModuleInfo>(moduleToImport);
            newOrChangedVars = new List<PSVariable>(variablesToSet);

            moduleToImport.Clear();
            variablesToSet.Clear();
        }

        if (newOrChangedModules.Count > 0)
        {
            // Import the modules with -Force
        }

        if (newOrChangedVars.Count > 0)
        {
            // Set or update the variables.
        }

        TargetActionEnabled = false;
    }

    public static PSEventSubscriber SubscribeOnIdleEvent(EngineIntrinsics engineIntrinsics, bool isSourceRunspace)
    {
        PSEventReceivedEventHandler handler = null;
        if (isSourceRunspace)
        {
            if (sourceEventSubscribed)
            {
                throw new InvalidOperationException("OnIdle even already subscribed in source Runspace.");
            }

            // Save the engineIntrinsics from source Runspace for later use.
            handler = (PSEventReceivedEventHandler) CollectSourceRunspaceState;
            sourceEngineIntrinsics = engineIntrinsics;
            sourceEventSubscribed = true;
        }
        else
        {
            if (targetEventSubscribed)
            {
                throw new InvalidOperationException("OnIdle even already subscribed in target Runspace.");
            }

            // Save the engineIntrinsics from target Runspace for later use.
            handler = (PSEventReceivedEventHandler) UpdateTargetRunspaceState;
            targetEngineIntrinsics = engineIntrinsics;
            targetEventSubscribed = true;
        }

        return engineIntrinsics.Events.SubscribeEvent(
            source: null,
            eventName: null,
            sourceIdentifier: PSEngineEvent.OnIdle.ToString(),
            data: null,
            handlerDelegate: handler,
            supportEvent: true,
            forwardEvent: false);
    }
}