Write thread pool code

I need a production thread pool implementation that supports submitting tasks with futures, a fixed number of worker threads configurable at construction, graceful shutdown that finishes pending tasks, and immediate shutdown that discards queued tasks. Implement submit, shutdown, and join in the .cpp, ensure tasks execute in FIFO order, and ship with a small benchmark that runs on my Ubuntu VM before code review on Friday.

Before I commit the thread pool, make it easy to reuse and safe under load. Put the constructor flags and their defaults at the top of the header, expose a simple submit-for-fire-and-forget and submit-with-future API, document behavior on shutdown and queue overflow, surface expected throughput numbers from the benchmark, and call out the failure modes that would make a reviewer hesitate.

I deployed a new thread pool and some producers are reporting missing work under burst load. I can't tell whether tasks are being dropped by the pool or failing earlier. I'm worried the default policy is silently discarding work. What checks and runtime assertions should I add to distinguish queue overflow from task failure, and what immediate config change or API tweak would stop data loss while we diagnose?

Every project here ends up reimplementing a thread pool with slightly different semantics; we waste time debugging edge cases and benchmarking again. Where should we converge: one library with configurable but well-documented policies, a small reference implementation with clear defaults, or conventions for when to use a simple std::async approach? Recommend the habit change and a migration plan to reduce duplicated effort and bugs.