Two gig-prep deliverables that needed no ears, written at J-10.

RUNBOOK.md (#15) — the "when it breaks" playbook, organised symptom-first because
that is how it actually gets read: you don't know the cause, you know the sound
stopped. Ordered cheapest-first, with an explicit rule zero that rebooting
SuperCollider is the LAST resort (30-120s of dead air and every pattern lost) and
almost nothing needs it.

The section worth having written down is 2b, the zombie control port. Observed live
today: a leftover ghc process holds Tidal's port 6010, so a fresh Tidal boots, fails
to bind, prints "Can't handshake with SuperCollider without control port" — and
Pulsar looks completely normal. You eval and nothing happens, with NO error surfaced
in the editor. That is the nastiest class of failure: silent, and indistinguishable
from "my code is wrong". Detection is one line (ss -lunp | grep 6010, expect exactly
one ghc and it should be the current one), so it's now in the pre-set checklist
rather than only in the recovery section.

Also captured: the mute-bomb rescue path (prelude.tidal as in-session hot-patch on a
stale boot, with the tell that pulling fader 49 to 0 makes it WORSE not better);
fader 77 being down as a silent global-gain failure that looks like nothing is
broken; Pulsar being frozen NOT stopping audio, since patterns live in ghci and not
the renderer, so Window: Reload keeps the music playing; and the LCXL USB-OUT
endpoint stall where LEDs die but input survives (replug).

Every procedure is labelled by how well it's actually established — §1a/2a/2b/2c/7
have commands verified by running them today, §4/§6 come from documented prior
incidents with known-good fixes but weren't re-tested tonight, and §5's gig-up.sh
path was read from source rather than exercised end to end. A runbook you have never
executed is a hypothesis, and it should say so.

docs/2026-07-25-opal-bpm-arc.md (#12 input) — read setcps out of all 12 setlist
tracks instead of trusting the backlog's [bpm] markers, and three disagree:
- Gimme Acid: 80 measured vs 160 written — almost certainly the standard dnb
  half-time convention, but it decides where the track sits in the arc.
- Sunshine: 144 measured vs 166 written. 22 BPM is far too big to be a rounding
  note, and it inverts the end of the set: the backlog plans Mafia(160) ->
  Sunshine(166) as a rising finish, but measured it is a 16 BPM DROP. Either the
  file drifted or the number was aspirational — needs a decision, since the shape
  of the finale depends on it.
- Desire: 127 vs 129. Trivial, but it's the FINALE, so make them agree.

Charted the measured arc and flagged three >40 BPM cliffs (->89, ->80, ->160). The
89 and 80 ones look deliberate — a slow track between fast ones is a real dramatic
move — and they are only a problem if the transition is unprepared, which is
precisely what the riser audit (#33) and default-xfade (#13) exist to fix. Also
noted the 124/124/128 plateau as the most transition-safe stretch in the set.

Ordering itself is left as PLN's call; this is only the tempo dimension.