fix: process leaks in extensionHostConnection

[SimonSiefke]

Fixes #211462.

Details

When the connection closes, the extension host sends a disconnect message, and then closes the socket. The remote agent host, receives the disconnect message, starts its graceful cleanup but then the socket close event comes which immediately triggers extHostSocket.destroy() before the graceful cleanup is finished

Change

The change tries to ensure the extHostSocket gets shutdown gracefully, so that the cleanup code and still run and finish.

Before

When opening a new window and connecting it to SSH and then closing it 3 times, the number of processes seems to increase each time:

{
  "processCount": {
    "after": 33,
    "before": 10
  },
  "isLeak": true
}

After

When opening a new window and connecting it to SSH and then closing it 3 times, the number of processes seems to stay constant:

{
  "processCount": {
    "after": 13,
    "before": 13
  },
  "isLeak": false
}

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Updates extension host socket disposal to perform a graceful shutdown rather than an immediate destroy, aiming to reduce abrupt termination during cleanup.

Changes:

• Replace extHostSocket.destroy() with a conditional extHostSocket.end() on dispose.
• Add guards to avoid ending an already-destroyed or already-ended socket.