Queues & Inter-Task Communication

In this lesson:

• the queue: a thread-safe, blocking FIFO for passing data between tasks
• copy semantics, and when to send a pointer instead
• the producer/consumer pattern (and the ISR variant)
• why a queue beats a shared global + mutex
• other IPC (task notifications, stream buffers, event groups) and the gotchas

A semaphore signals "something happened"; a queue carries the what.