Implement MCP stdio shutdown spec compliance with graceful shutdown manager

[Copilot]

The MCP stdio transport shutdown implementation was not following the MCP specification. Previously, it used AbortController.abort() to immediately terminate processes, but the spec requires a graceful shutdown sequence.

Changes Made

Replaced the simple abort controller approach with a new McpStdioConnectionManager class that implements the exact shutdown sequence specified in the MCP specification:

1. Close input stream: Calls stdin.end() to gracefully close communication with the server
2. Wait for natural exit: Gives the process 2 seconds to exit cleanly
3. Send SIGTERM: If still running, sends SIGTERM and waits another 2 seconds
4. Send SIGKILL: If still unresponsive, forces termination with SIGKILL
5. Force kill on double call: If $stopMcp called twice, immediately sends SIGKILL

Key Features

• Platform-aware termination: Uses taskkill on Windows, process.kill on POSIX systems
• Memory efficient: Proper timeout cleanup prevents memory leaks
• Error resistant: Handles edge cases like stdin stream errors gracefully
• Non-breaking: Maintains all existing functionality and interfaces
• Spec compliant: Follows MCP specification requirements exactly

Implementation Details

The new McpStdioConnectionManager class:

• Manages the graceful shutdown state machine
• Uses 2-second grace periods as specified
• Handles platform-specific process termination
• Provides proper cleanup and error handling
• Integrates seamlessly with existing MCP infrastructure

Before:

nodeServer.abortCtrl.abort(); // Immediate termination

After:

nodeServer.connectionManager.stop(); // Graceful shutdown sequence

This ensures MCP servers have proper opportunity to clean up resources and exit gracefully, improving reliability and following the established protocol specification.

Fixes #250206.

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