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MCP Dispatch: In-Host Primitive Execution

Overview

MCP tools and resources execute inside the host process behind an SDK McpServer on DevToolsMcp_*. Each pipe connection gets McpServer.Create(StreamServerTransport, …) with tools/resources populated from McpCatalogStore and invoked via IMcpSource backends on the host thread.

Source Map

File Role
source/DevTools.Mcp.Catalog/Transport/McpPipeServer.cs Accept loop; per-connection PipeEndpoint + SDK server
source/DevTools.Mcp.Catalog/Hosting/McpServerCollections.cs Fill SDK tool/resource collections from catalog
source/DevTools.Mcp.Catalog/Core/Protocol/McpSpecKeys.cs Wire names (Tool.Invoke = invoke_dynamic, etc.)
source/DevTools.Mcp.Catalog/McpCatalogStore.cs RegisteredTool / RegisteredResource / RegistryCatalog
source/DevTools.Mcp.Catalog/Discovery/ResultBridge.cs toolset object → host CallToolResult
source/DevTools.Execution/External/Mcp/Backends/*.cs BuiltInSource, DotnetSource, PythonSource
source/DevTools.Execution/External/Mcp/Hosting/McpCallFilter.cs Host InputRequiredException → wire shape
source/DevTools.Execution/External/DevToolsPipeServer.cs Pytest/control pipe only

Execution Flow

sequenceDiagram
    participant Daemon as HostConnections
    participant Pipe as DevToolsMcp_* pipe
    participant Server as McpPipeServer / McpServer
    participant Source as IMcpSource
    participant Host as IHostContextExecutor

    Daemon->>Pipe: tools/call {name, arguments, _meta}
    Pipe->>Server: SDK session handler
    Server->>Source: CatalogToolAdapter.InvokeAsync
    Source->>Host: ExecuteAsync (main thread)
    Host-->>Source: CallToolResult
    Source-->>Daemon: CallToolResult (wire JSON)
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Backend Routing

Routing uses RegisteredTool.Binding (PrimitiveBinding) and SourceKind:

Backend Invoke mechanism
Built-in C# (IBuiltInMcpTool) BuiltInSource
.NET toolset (ALC) DotnetSource + ResultBridge.ToHostCallToolResult
Python toolset PythonSource + ToolInvoke.py (SDK in-process client)

See Platform boundaries for MRTR and ALC detail.