C library selection

Same include/exclude rule as Python: measure local handoff. Brokers are category N. Job runners are not queues.

C has almost no commonly packaged in-process FIFO on the host (no crates.io / PyPI analog). liblfds and Concurrency Kit are real libraries but they are system packages with a heavy build story. This pass vendors one small, BSD-2-Clause lock-free MPMC instead of adding a new host requirement.

Decision

Decision	Libraries
Already in	mutex-queue, spsc-ring, steal-deque, opt-in P/S/D
Added	lfqueue (vendored Taymindis/lfqueue)
Out — host-heavy lock-free kits	liblfds, Concurrency Kit (ck_ring / ck_fifo)
Out — category N	nanomsg / nng, ZeroMQ, hiredis, librdkafka

In this lab

Log name	Category	Why
mutex-queue	T / locked	pthread mutex + condvar ring. Already present.
lfqueue	T / concurrent	Vendored lock-free MPMC FIFO. The analog of Rust crossbeam-queue. Added.
spsc-ring	T / spsc	Harness ring. Already present.

lfqueue has no condvar; wakeup cells are skipped (spin-only empty pop).