Implement interface methods

Implement the methods for the input handler interface used by the audio engine: initialize with a sample rate, submit a block of float samples for processing, query latency in milliseconds, and shut down releasing all resources. Keep thread-safety guarantees in comments and ensure the submit method is noexcept and returns a boolean for acceptance. Provide method implementations ready to drop into a .cpp.

Before I hand this interface implementation to QA, make it obvious how callers should use it. Put the expected thread model up top, document return values for backpressure, surface the latency number and its units, and flag any implementation choices that would make a reviewer hesitate, such as sleeping in submit, hidden global state, or allocation per submit.

Submit started returning false intermittently during stress tests; I think it’s backpressure but I don’t know whether it’s queue sizing, a lock contention bug, or a scheduler issue. What’s the most likely diagnosis and the single best change to make now so callers degrade gracefully while I debug further?

Every release our input handler implementations show different failure modes under load and we waste days chasing each. Where are we losing time and accuracy in our approach, and what two habits should we adopt — one design habit (bounded lock-free queues or capacity contracts) and one team habit (a reproducible load test in CI) — to stop this recurring firefight?