Avoid embedding the parent's sys.argv into the forkserver -c command
string via repr(). When sys.argv is large (e.g. thousands of file
paths from a pre-commit hook), the resulting single argument could
exceed the OS per-argument length limit (MAX_ARG_STRLEN on Linux,
typically 128 KiB), causing posix_spawn to fail and the parent to
observe a BrokenPipeError.
Instead, append the argv entries as separate command-line arguments
after -c; the forkserver child reads them back as sys.argv[1:]. This
cannot exceed any limit the parent itself did not already satisfy.
Regression introduced by gh-143706 / 298d5440eb.
5e9d90b615