Capture user_id/account_id before try block so error handler survives
db.rollback() without triggering lazy loads in async context. Add
retry-without-MCP fallback when Anthropic MCP server returns rate limit
or connection errors.
Fixes PYTHON-FASTAPI-3, PYTHON-FASTAPI-4
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>