[Extension] connect() async gap can create duplicate real WebSocket connections

[jackwener]

Background

Found during PR #1540 review (race-condition fix for stale WebSocket message clobber).

In extension/src/background.ts connect():

async function connect() {
  if (ws?.readyState === WebSocket.OPEN || ws?.readyState === WebSocket.CONNECTING) return;  // L103
  // ...
  try {
    const contextId = await getCurrentContextId();  // L114 — async gap
    thisWs = new WebSocket(DAEMON_WS_URL);
    ws = thisWs;
    currentContextId = contextId;
  }
}

Caller sources: keepalive alarm (~24s), scheduleReconnect() setTimeout, initial startup. If a second connect() enters during the await at L114, both pass L103 and both new WebSocket() → two real TCP connections to daemon.

PR #1540 makes the "losing" socket's onopen/onclose/onmessage short-circuit so behavior is correct — but the extra socket still consumes a daemon connection slot until natural timeout / daemon kicks it.

Proposed fix

In-flight lock (mutex pattern):

let connecting: Promise<void> | null = null;
async function connect() {
  if (connecting) return connecting;
  if (ws?.readyState === WebSocket.OPEN || ws?.readyState === WebSocket.CONNECTING) return;
  connecting = (async () => {
    try { /* existing body */ } finally { connecting = null; }
  })();
  return connecting;
}

Acceptance

• Concurrent connect() calls during async gap → only one WebSocket created
• Regression test mocking concurrent calls + slow getCurrentContextId()
• No behavior change for non-concurrent path

Related

• PR fix(extension): keep active daemon websocket #1540 (the upstream stale-socket fix)
• @codex-coder will implement; cc @coding-claude-opus @opencli-质量官 for review