[BUG] MCP server push notifications silently ignored by Claude Code on Windows 11 ARM64

Preflight Checklist

• [ ] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

When an MCP server sends an unsolicited notification to Claude Code (e.g., a Discord
message arriving via the Discord plugin), Claude Code never processes it. The session
remains completely idle despite the notification being successfully delivered.

Manual tool calls (fetch_messages, reply) work correctly. Only push notifications
(server-initiated) are ignored.

What Should Happen?

Claude Code should process incoming MCP server notifications and respond accordingly —
in this case, reading the Discord message and replying in the channel.

Error Messages/Logs

[2026-05-08T06:24:11.047Z] gateway ready: connected as <bot_name>#XXXX
  [2026-05-08T06:24:58.895Z] messageCreate: user=<user_id> channel=<channel_id> content="test message"
  [2026-05-08T06:24:58.898Z] mcp.notification: sending channel notification for message_id=<message_id>
  [2026-05-08T06:24:58.898Z] mcp.notification: delivered OK message_id=<message_id>

Steps to Reproduce

1. Enable the Discord plugin and start a Claude Code session.
2. Confirm the MCP server is connected: run /mcp → should show

plugin:discord:discord · ✔ connected · 5 tools

1. Send a message from Discord to the bot.
2. Observe that Claude Code does not react — the session stays idle.
3. To confirm the message was received, manually call fetch_messages —

the message appears correctly.

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

v2.1.133

Platform

Other

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

Additional Information

• MCP server runtime: Bun v1.2.13
• Plugin: plugin:discord:discord (official Claude plugin, v0.0.4)
• /mcp shows the server as "connected" with all 5 tools available
• Discord Gateway MESSAGE CONTENT INTENT: enabled and verified
• Clean reinstall of Claude Code via npm uninstall -g / npm install -g: no improvement
• mcp.notification() resolves successfully (Promise fulfilled, no exception),

but Claude Code never acts on the notification content

CPU is ARM64 (Snapdragon X1E-78). This may be relevant if stdio/pipe notification
handling differs between ARM64 and x64 Windows builds of Node.js or Bun —
x86/x64 behavior on this specific code path has not been verified on this machine.

Hypothesis: Claude Code's MCP notification reader loop on Windows ARM64 may have a
pipe-buffering or event-loop issue that prevents it from waking the session when an
unsolicited notification arrives on the MCP server's stdout.