fix: prevent stdout drain listener accumulation in long-running sessions

[sorlen008]

Summary

Fixes wonderwhy-er#391 — during extended Claude Desktop sessions with heavy tool usage (50+ tool calls), Desktop Commander emits MaxListenersExceededWarning on process.stdout and tool calls begin timing out.

Root cause

sendLogNotification, sendLog, sendProgress, and sendCustomNotification all wrote to stdout by calling originalStdoutWrite directly in a fire-and-forget manner — no backpressure handling. When the stdout buffer fills up under heavy load:

1. Each in-flight MCP SDK send() call registers process.stdout.once('drain', resolve) while waiting for the buffer to drain
2. Meanwhile, the direct originalStdoutWrite calls keep adding data to the buffer, delaying drain
3. With 11+ concurrent send() calls pending, Node.js emits MaxListenersExceededWarning (default limit: 10)
4. Sessions degrade: tool call responses are delayed or timeout

Fix

Serialised notification write queue (writeNotificationToStdout / flushNotificationQueue): all notification/progress/custom writes now go through a queue that registers at most one once('drain', ...) listener at a time. When stdout drains, the queue flushes sequentially. This eliminates the listener pile-up while also preventing dropped notifications (previously originalStdoutWrite returning false silently discarded the write).

process.stdout.setMaxListeners(50) in the constructor: defence-in-depth for the SDK's own legitimate concurrent drain listeners during bursts of parallel tool responses.

Changes

• src/custom-stdio.ts:
  • Add stdoutQueue: string[] and stdoutDraining: boolean fields
  • Add writeNotificationToStdout(data) and flushNotificationQueue() methods
  • Replace all 8 direct originalStdoutWrite.call(...) calls in notification methods with writeNotificationToStdout(...)
  • Call process.stdout.setMaxListeners(50) in constructor

No breaking changes

Normal write path for JSON-RPC responses (through setupStdoutFiltering) is unchanged. The queue only affects the custom notification write path.

Test plan

• Start a long session (50+ tool calls mixing read_file, list_directory, start_process, edit_block)
• Confirm mcp-server-desktop-commander.log shows no MaxListenersExceededWarning
• Confirm drain listener count stays at 1 in logs (add process.stdout.listenerCount('drain') trace if needed)
• Confirm all log notifications are delivered (no silent drops under load)
• npx tsc --noEmit passes with zero errors

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