Desktop の更新後に MCP Apps の画面が出なくなったら — stdio の間に記録係を挟んで、誰が何を頼んだかを数える

#!/usr/bin/env python3
"""stdio MCP サーバーの手前に挟み、行き来した JSON-RPC を1行ずつ記録する。
使い方: python3 mcp_tap.py --log ~/mcp_tap.log -- <本来のコマンド> [引数...]
"""
import json, os, subprocess, sys, threading, time
 
args = sys.argv[1:]
log_path = os.path.expanduser("~/mcp_tap.log")
if args[:1] == ["--log"]:
    log_path, args = os.path.expanduser(args[1]), args[2:]
if args[:1] == ["--"]:
    args = args[1:]
if not args:
    sys.exit("usage: mcp_tap.py [--log PATH] -- command [args...]")
 
# stdout は MCP の通信路なので、記録は必ずファイルへ（print は使わない）
child = subprocess.Popen(args, stdin=subprocess.PIPE, stdout=subprocess.PIPE)
lock = threading.Lock()
pending = {}            # 問いの id -> method（返事を引き当てるため）
client = {"name": "?"}  # initialize で名乗ったクライアント名
 
def describe(direction, msg):
    if direction == "->":
        method = msg.get("method", "-")
        if "id" in msg:
            pending[msg["id"]] = method   # 子へ渡す前に登録する（返事との競争を避ける）
        if method == "initialize":
            client["name"] = msg.get("params", {}).get("clientInfo", {}).get("name", "?")
        if method == "resources/read":
            return method, f"uri={msg.get('params', {}).get('uri')}"
        return method, ""
    method = pending.pop(msg.get("id"), "-")
    result = msg.get("result") or {}
    if method == "tools/list":
        tools = result.get("tools", [])
        ui = [t["name"] for t in tools if (t.get("_meta") or {}).get("ui", {}).get("resourceUri")]
        return method, f"tools={len(tools)} with_ui={ui} next={bool(result.get('nextCursor'))}"
    if method == "tools/call":
        return method, f"meta={sorted((result.get('_meta') or {}))} error={'error' in msg}"
    return method, ""
 
def log(direction, msg, note):
    stamp = time.strftime("%Y-%m-%dT%H:%M:%S", time.gmtime())
    with lock, open(log_path, "a", encoding="utf-8") as f:
        f.write(f"{stamp}Z pid={os.getpid()} client={client['name']} "
                f"{direction} {msg[0]} id={msg[1]} {note}\n")
 
def pump(src, dst, direction):
    for raw in iter(src.readline, b""):
        try:
            msg = json.loads(raw)
            method, note = describe(direction, msg)
            ident = msg.get("id", "-")
        except ValueError:
            method, note, ident = "non-json", raw[:60], "-"
        dst.write(raw)
        dst.flush()
        log(direction, (method, ident), note)
    if direction == "->":
        child.stdin.close()
 
threading.Thread(target=pump, args=(sys.stdin.buffer, child.stdin, "->"), daemon=True).start()
pump(child.stdout, sys.stdout.buffer, "<-")
sys.exit(child.wait())

{
  "mcpServers": {
    "my-local-app": {
      "command": "/usr/bin/python3",
      "args": [
        "/Users/you/mcp/mcp_tap.py",
        "--log", "/Users/you/mcp_tap.log",
        "--",
        "/usr/local/bin/node", "/Users/you/mcp/server.js"
      ]
    }
  }
}

# 接続ごとの名乗りと、ツール呼び出し・画面の取得だけを時刻順に並べる
grep -E ' -> (initialize|tools/call|resources/read) ' ~/mcp_tap.log | awk '{print $1, $2, $3, $5, $7}'
# 定義の側に画面の URI が付いているか
grep ' <- tools/list ' ~/mcp_tap.log | tail -3