PLN picked SUBTLE from the three-way close A/B. Promoting it exposed two bugs
that would each have shipped something he never heard.

1. The reverb existed TWICE and the copies disagreed. render_release had a
   single 833ms slap (aecho=0.8:0.5:833:0.35) applied to the WHOLE track;
   build_release_joins had a three-tap preset applied to the tail only. Setting
   `reverb_tail_s` would therefore have washed all of REVOLUTION with an echo
   nobody auditioned. The preset table now lives in render_release and the A/B
   builder imports it, so what ships is bit-for-bit the chain he compared.

2. apply_boundaries forwarded edit keys through an ALLOW-list, which silently
   dropped `reverb_preset`; the renderer then saw no preset and fell back to no
   reverb at all. A missing edit is invisible in the output — you get a clean
   render of the wrong thing — so it now deny-lists the keys it consumes and
   forwards everything else.

Caught by inspecting the built filter graph before rendering rather than after,
which is the only reason this is a commit message and not a re-render.

The tail reverb is a split graph, not `-af`: head dry, last 5s through apad then
aecho, concatenated. The apad matters — without it ffmpeg chops the ring at the
final sample, reintroducing the exact hard stop the reverb exists to soften.
Verify accounts for the 2.5s ring, so REVOLUTION is expected at 207.4s not
204.9s rather than being flagged as a mismatch.