Implements `timeoutChecker`, a self-contained heartbeat timeout monitor with callbacks for timeout and reconnection events. It uses atomic operations and channels to track last alive time, supports multiple registered callbacks, and provides `waitUntilReconnected()` blocking. This is a reusable component for any Go application needing connection health monitoring without external dependencies.

Provides `replaceableStream` and `interruptibleStream` implementations that allow hot-swapping the underlying I/O stream without losing data or causing race conditions. The design uses condition variables, atomic booleans, and channel-based synchronization to safely replace a stream at runtime. This pattern is reusable for any scenario requiring live stream replacement (e.g., reconnection, session migration) and demonstrates non-trivial concurrency handling.

A complete parser for OpenSSH sshd_config files, including Match block evaluation with User, Group, and All criteria, subsystem registration, and AcceptEnv handling. It correctly handles key-value formats with or without '=', wildcard patterns for user/group matching, and provides a query interface via `getSshdConfig()`. This is a standalone module that can be reused by any Go tool needing to read OpenSSH configuration.