Previous commit tried to enable AES-NI via target-cpu=x86-64-v3 but
that microarchitecture level does NOT include AES-NI — it's a separate
ISA extension added on top. The aes crate kept falling back to software
decrypt (~10 MB/s), so the first live test still showed a 6s gap on
offline-cache gapless for a 58 MB track (~10 MB/s).
Fix: add target-feature=+aes,+ssse3 to rustflags. The aes crate's
runtime dispatch via cpufeatures only works if the AES-NI code path
was actually compiled in, which requires the build-time feature flag.
Expected: 58 MB decrypt drops from ~6s to ~150ms, fits inside the 5s
gapless pre-emptive window with headroom.
cc
vicrodh
d5ef97b84f