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reentrancy-patterns

Comprehensive reentrancy attack patterns and defenses for Solidity. Use when writing contracts with external calls, integrating tokens with callbacks (ERC-777, ERC-1363), or auditing for reentrancy vulnerabilities. Covers all variants including read-only reentrancy.

skills/reentrancy-patterns/SKILL.md

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Oct 23, 2026
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# Reentrancy Patterns

## Single-Function Reentrancy

The classic variant. An external call re-enters the same function before state is updated.

```solidity
// VULNERABLE: state update after external call
contract VulnerableVault {
    mapping(address => uint256) public balances;

    function withdraw(uint256 amount) external {
        require(balances[msg.sender] >= amount);