The sellTokens() function at lines 493-549 violates the Check-Effects-Interactions (CEI) pattern by performing an external token transfer before updating critical state variables. Specifically, the function receives MyTokens from the user via safeTransferFrom() at line 530, and only afterwards updates the bonding curve state by decrementing curve.totalSold and currentLiquidity at lines 533-534. The CEI pattern is a fundamental security best practice in Solidity that mandates all state changes must occur before any external calls to prevent reentrancy vulnerabilities. In a standard implementation without additional protections, this ordering would create a critical reentrancy vulnerability where a malicious token contract could reenter the function during the safeTransferFrom call and execute additional sells using the not-yet-updated state, potentially draining the contract through repeated transactions that reference stale totalSold and currentLiquidity values. However, this theoretical vulnerability is fully mitigated by the nonReentrant modifier from OpenZeppelin's ReentrancyGuard that is applied to the function at line 495, which sets a mutex preventing any reentrant calls. Additionally, the MyToken contract is deployed and controlled by the PumpFunComplex contract itself (created at line 168 in the constructor), making it a trusted internal token rather than an external potentially-malicious contract.

The buyTokens() function at lines 551-632 may fail to trigger graduation in edge cases where a purchase brings liquidity very close to but not exactly at the target. The graduation logic at lines 606-612 uses a tolerance of GRAD_TOLERANCE_ATOMS * _scalingFactor (5 × 10^-12 for USDT) to determine if the contract should snap to the target and graduate. This tolerance is designed for sub-atomic rounding precision but is too small to handle realistic near-completion scenarios. For example, if the target is 10,000 USDT and current liquidity is 9,995 USDT, a purchase of 3.96 USDT results in 9,998.96 USDT total, leaving a 1.04 USDT gap. The tolerance check (9,998.96 + 0.000005 >= 10,000) fails, preventing graduation despite being 99.99% complete. The triple graduation detection at line 625 (isFinalPurchase || balanceClose || _reachedTarget()) also fails because all three conditions evaluate to false when the gap exceeds the microscopic tolerance. This leaves the contract at 99.9%+ completion, requiring another user to purchase the remaining small amount. While not a security vulnerability and eventually self-resolving with the next purchase, this creates suboptimal UX and potential confusion, especially if the remaining gap is very small and disincentivizes further participation.