Codex adds an MCP notification so stdio servers learn when the user logs out or switches accounts.

PR #43428 advertises a codex/auth-change capability on stdio MCP connections with an auth manager, then sends notifications/codex/authChanged after initialization and on every subsequent auth change (GitHub). The payload carries credential and owner generation counters and no credentials, tracking owner changes separately from credential refreshes so a server can distinguish a token refresh from a login, logout or workspace switch even when notifications coalesce. Sends cap at five seconds and a failed follow-up closes the connection.