Fix LSP client on Windows: stream reading and server request handling

[ronti1]

Fix LSP client on Windows: stream reading and server request handling

Problem

The LSP client fails on Windows with two issues:

1. Stream reading hangs: ReadContentLengthAsync reads from Process.StandardOutput.BaseStream byte-by-byte, which silently fails on Windows pipes. The .NET Process class wraps stdout in a StreamReader with internal buffering — reading the underlying BaseStream bypasses this buffer, causing ReadAsync to never receive data even though csharp-ls writes correctly.

2. Server requests dropped: ProcessMessage treats all messages with an id field as responses to client requests. However, csharp-ls sends server-to-client requests (e.g., client/registerCapability, workspace/configuration) that have both id and method fields. These are silently dropped, causing csharp-ls to block waiting for responses and never process subsequent requests.

Fix

Stream reading — replaced BaseStream byte-by-byte reading with StreamReader.ReadLineAsync() for headers and StreamReader.ReadAsync(Memory<char>) for body content. Set StandardOutputEncoding = new UTF8Encoding(false) to ensure consistent encoding.

Server requests — updated ProcessMessage to distinguish three JSON-RPC message types:

• id + method → server request → auto-respond with {result: null}
• id only → client response → dispatch to pending TCS
• method only → notification → handle/log

Added SendServerResponseAsync that builds JSON manually to avoid WhenWritingNull stripping the result: null field.

Testing

Verified on Windows with csharp-ls 0.22.0 (.NET 10):

• set_workspace → loads solution successfully
• csharp_symbols → returns document symbols
• csharp_hover, csharp_definition, csharp_references → all working
• All 9 MCP tools tested and passing