> ## Documentation Index
> Fetch the complete documentation index at: https://docs.cow.bleu.builders/llms.txt
> Use this file to discover all available pages before exploring further.

# System Architecture

> Understanding the Flash Loan Router's modular design, component interactions, and execution flow

## Overview

The Flash Loan Router employs a modular design separating routing logic, lender-specific adapters, and settlement execution. This enables support for multiple flash loan providers while preserving security and predictable execution.

## Components

The system consists of four main components:

1. **Flash Loan Router** - Core orchestrator for flash loans and settlement
2. **Borrower adapters** - Lender-specific contracts handling protocol differences
3. **Flash loan lenders** - External protocols (Aave, Maker) providing liquidity
4. **CoW Settlement** - Target contract executing trades

## Execution Flow

The system processes settlements through four phases:

**Phase 1:** A solver calls `flashLoanAndSettle()` with loan specifications and settlement data.

**Phase 2:** The router requests loans sequentially from each borrower adapter, which triggers lender-specific callbacks.

**Phase 3:** Once all loans are received, the router executes the settlement contract with the provided data.

**Phase 4:** Lenders pull repayment from borrower contracts through ERC-20 transfers.

## Core Security Guarantees

The router maintains these critical properties:

* Only registered CoW Protocol solvers can call `flashLoanAndSettle()`
* Exactly one settlement call per loan request, using unmodified data
* Sequential loan processing prevents out-of-order execution
* Atomic execution -- all operations succeed or fail together

## Supported Lenders

* **Aave V3** via AaveBorrower
* **ERC-3156 compatible** providers (including Maker) via ERC3156Borrower

New lenders can be added by creating borrower contracts implementing the lender's callback interface without modifying core router code.