[Bug]: `avdt mcp` `attach-to-app` / `attach-to-file` always times out (cross-platform, 2.2.0-beta2)

[C5T8fBt-WY]

Describe the bug

Both attach-to-app and attach-to-file MCP tool calls return TimeoutException after ~5 seconds. The MCP server discovers the app correctly (availableClients returns app name/PID), but the connection step always fails.

The DevTools GUI mode (avdt --connect --session-id X --http-port 29414) works perfectly.

To Reproduce

1. Install avdt 2.2.0-beta2: dotnet tool install --global AvaloniaUI.DeveloperTools --prerelease
2. Add AvaloniaUI.DiagnosticsSupport 2.2.0-beta2 to any Avalonia 11.x app
3. Call this.AttachDeveloperTools() in App.Initialize() under #if DEBUG
4. Configure MCP in .vscode/mcp.json:

   {
     "servers": {
       "avalonia_devtools": {
         "type": "stdio",
         "command": "avdt",
         "args": ["mcp"],
         "env": { "ACCELERATE_LICENSE_KEY": "avln_on_key:v1:..." }
       }
     }
   }

5. Start the app, invoke attach-to-app via any MCP client (VSCode, Claude Code, etc.)

Expected: Connection established, MCP tools (tree, search, props, etc.) return data
Actual: TimeoutException after ~5 seconds

Product(s)

DevTools

Platform

Windows, Linux

Accelerate Tier

Trial

Avalonia version

11.3.3

Accelerate Version

No response

Relevant log output

Starting HTTP server: DevToolsTargetListenerOptions { HttpsPort = , HttpPort = 39141, ListenAnyIp = False }
Failed to connect to client with process ID 35771
System.TimeoutException: The operation has timed out.
  at AvaloniaUI.DeveloperTools.Mcp.McpDevToolsConnection.<ConnectToClientAsync>d__19.MoveNext()

Additional context

1. Discovery pipe exists, app IS listening:

$ lsof -p <APP_PID> | grep CoreFx
StabilityS <APP_PID> lilyknight 172u unix 0x00 0t0 541826 /tmp/CoreFxPipe_Global.AVDT.Discovery type=STREAM (LISTEN)

2. MCP server process NEVER opens the discovery pipe:

$ lsof -p <MCP_PID> | grep -i "CoreFx\|AVDT"
(no output)

The MCP process has only stdio Unix sockets (fd 0,1,2,5,6,9,13 — all connected to the editor).

3. MCP ignores settings.json httpPort:

• settings.json has "httpPort": 29414
• GUI mode: uses 29414 ✓
• MCP mode: uses random ports (38105, 39141, 35463 observed across multiple runs) ✗

4. Connection CAN be established via workaround:
Using ConnectOnStartup = true + Protocol = CreateHttp(Loopback, 29414) + a TCP forwarder (port 29414 → MCP's random port), the app successfully connects:

# MCP log after workaround:
Target connected, SessionId: 7tdgWeOcmKu, ProtocolVersion: 1.1.0

5. attach-to-app ignores existing connections:
Even after the app is successfully connected (see workaround above), calling attach-to-app again still times out. It always attempts a fresh discovery pipe approach instead of checking for existing connected sessions.

[jpgarza93]

I am seeing the same issue on my MacBook

[msivers]

There should be a fix for this in 2.2.0-beta3 which will hopefully be out some time next week (w/c 23rd Feb).