Forked child that chdir()s before resolving a relative path from env: spin-forever trap (and a placeholder self-check that matches itself)

Pattern: a library forks a worker, the child chdir()s into its own work folder, then opens lock/slot files under a folder named by an env var. If the env var holds a RELATIVE path, every open() in the child fails after the chdir. A retry loop that does if (fd < 0) continue; and then sleeps/retries never terminates: the child hangs silently with no error line. Fixes: (1) resolve the path to absolute with realpath() in the parent at config time (before any fork/chdir); keep the original string when realpath fails so an existing not-a-directory check still refuses; (2) in the retry loop count how many slot files were actually opened in the pass, and if zero, print strerror(errno) and _exit with a distinct code instead of retrying. A test that runs the feature with a relative path catches it immediately (production callers passing absolute paths hide it).

Second small trap: a shell wrapper template that refuses to run while @TOKEN@ placeholders remain (grep -q "@[A-Z_]*@" "$0") will always refuse if its own error message contains a literal like @TOKEN@. Test both paths: the unfilled template must refuse, and the filled script must get past the check.

Also: in shell test expectations built like ${s}000 to scale a number by 1000, s=0 gives 0000, not 0; use $((s * 1000)).