Refactor Node IDs for taskhost to use record struct

[Copilot]

Fixes #12610

Context

Follow-up to #12577. The taskhost node identification used bit-packing to combine scheduledNodeId (8 bits) and HandshakeOptions (9 bits) into a single int, limiting multithreaded builds to 256 nodes. This approach was fragile and hard to maintain.

Changes Made

• New TaskHostNodeKey record struct in CommunicationsUtilities.cs combining HandshakeOptions and NodeId as a clean, type-safe key
• Updated NodeProviderOutOfProcTaskHost with optimized dictionary structure:
  • _nodeContexts keyed by TaskHostNodeKey for checking if a node with given (HandshakeOptions, scheduledNodeId) exists (acquisition logic)
  • _nodeIdToNodeKey for O(1) reverse lookup during node termination
  • _nodeIdToPacketFactory and _nodeIdToPacketHandler keyed by int for O(1) packet routing performance
  • _activeNodes tracks node IDs (int) for shutdown handling
  • Added atomic _nextNodeId counter for unique communication node ID generation
• Simplified TaskHostTask - removed GenerateTaskHostNodeId method and associated bit-packing constants
• Improved error handling - Added VerifyThrow assertions in DisconnectFromHost and CreateNode to verify context existence and prevent duplicate nodes

// Before: bit-packed int with 256-node limit
_taskHostNodeId = GenerateTaskHostNodeId(_scheduledNodeId, _requiredContext);
// (scheduledNodeId << 9) | ((int)handshakeOptions & 0x1FF)

// After: clean record struct, no limit
_taskHostNodeKey = new TaskHostNodeKey(_requiredContext, _scheduledNodeId);

This gives the best of both worlds:

• Maintainability: Type-safe Keys for managing node lifecycle and acquisition
• Performance: Direct Integer lookups for the high-frequency packet routing hot path

Testing

• Added 7 unit tests for TaskHostNodeKey (equality, hash codes, dictionary keys, large node IDs)
• All 86 existing TaskHost tests pass

Notes

• Removes the NODE_ID_MAX_VALUE_FOR_MULTITHREADED (255) constraint entirely
• SendData(int, INodePacket) throws NotImplementedException as it's required by INodeProvider interface but not used for task hosts (similar to TaskHostNodeManager)

Original prompt

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This section details on the original issue you should resolve

<issue_title>[multithreaded] Refactor Node IDs for taskhost</issue_title> <issue_description>followup to dotnet/msbuild#12577 Refactor src/Build/BackEnd/Components/Communications/NodeProviderOutOfProcTaskHost.cs , HandshakeOptions to use record struct as a key to nodes to increase maintanability and remove limitation to 256 nodes.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes dotnet/msbuild#12610

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Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

[!WARNING]

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• rcxvsblobprodcus328.vsblob.vsassets.io
  • Triggering command: /home/REDACTED/work/msbuild/msbuild/artifacts/bin/bootstrap/core/dotnet dotnet test src/Build.UnitTests/Microsoft.Build.Engine.UnitTests.csproj --filter FullyQualifiedName~TaskHost --no-build -v n (dns block)

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[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

[!WARNING]

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• rcxvsblobprodcus328.vsblob.vsassets.io
  • Triggering command: /home/REDACTED/work/msbuild/msbuild/artifacts/bin/bootstrap/core/dotnet dotnet test src/Build.UnitTests/Microsoft.Build.Engine.UnitTests.csproj --filter FullyQualifiedName~TaskHost --no-build -v n (dns block)

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[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

[!WARNING]

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• rcxvsblobprodcus328.vsblob.vsassets.io
  • Triggering command: /home/REDACTED/work/msbuild/msbuild/artifacts/bin/bootstrap/core/dotnet dotnet test src/Build.UnitTests/Microsoft.Build.Engine.UnitTests.csproj --filter FullyQualifiedName~TaskHost --no-build -v n (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

[!WARNING]

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• rcxvsblobprodcus328.vsblob.vsassets.io
  • Triggering command: /home/REDACTED/work/msbuild/msbuild/artifacts/bin/bootstrap/core/dotnet dotnet test src/Build.UnitTests/Microsoft.Build.Engine.UnitTests.csproj --filter FullyQualifiedName~TaskHost --no-build -v n (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

[JanProvaznik]

https://devdiv.visualstudio.com/DevDiv/_git/VS/pullrequest/695704 passed