AI coding agents often introduce subtle bugs when modifying full-stack applications. These agents can alter backend API parameters or model fields, leading to backend unit tests passing while frontend code breaks silently in production. This disconnect occurs because backend tests don't catch frontend-side implications. To address this, StackBridge-MCP has been developed as an open-source Model Context Protocol server. It monitors cross-boundary contracts locally without necessitating heavy test virtual machines. StackBridge-MCP utilizes Tree-sitter for Abstract Syntax Tree extraction to parse frontend and backend code relationships. Relationships are stored in a SQLite database using Recursive Common Table Expressions, enabling very fast graph traversal. A baseline-diffed verification process checks for syntax and contract drift with high accuracy. Diagnostic ranking, using a breadth-first search, prioritizes errors and generates patches. Benchmarks show a significant reduction in context window size and dramatically faster traversal times. StackBridge-MCP also verifies code compilation with zero false positives and verifies all automated tests. It can be easily run with minimal configuration using a simple command.