Proxyline is a Node.js library that installs a process-wide proxy routing policy across `node:http`, `node:https`, undici/fetch, WebSocket clients, and explicit HTTP CONNECT tunnels. It provides two modes: `managed` (fail-closed with a required proxy URL) and `ambient` (respects `HTTP_PROXY`/`HTTPS_PROXY`/`NO_PROXY` environment variables). The library patches global HTTP(S) methods, replaces global agents, installs a custom undici dispatcher, and patches fetch globals. It includes observability via `explain()` and lifecycle events, scoped proxy TLS trust, dynamic bypass registrations, and credential-safe URL redaction. The codebase is TypeScript, ESM-only, and requires Node.js 22.19+ with undici 8.5+ as a peer dependency. It is well-tested with an in-process proxy lab and has comprehensive documentation.