Split kit and keys; KEYS GEN with MOTIF, 303, TURING, ARP

- genome(seed, salts) now has three parts with their own RNG streams:
  shared (steps, form, swing, arc, layback, fill odds, phase offset),
  kit (density, frame, accent cycle, free snare) and keys (scale/root,
  progression, motif, hocket, bass tone, note lengths, range). ROLL KEYS
  now renews the harmony too; ROLL KIT leaves the keys alone.
- Keys generators share one signature and can fix note lengths:
  MOTIF (the old line), 303 (acid bass, answers in the rests, drone or
  silent pad), TURING (8/16-bit shift register, DRIFT flips bits, 16-bar
  window), ARP (triad/7th arpeggio, roots on kicks).
- Pages: KIT GEN, KEYS GEN; ROLL shows KIT / KEYS; slots keep both gens.
- Flash record v3 (old settings ignored). Bring-up golden checksums updated.
- C port matches; host test and ASan/UBSan pass.

Intended music change: every seed sounds different (genome split, new
generators). Vectors regenerated with npm run vectors; the case grid now
crosses all kit and keys generators, with TURING runs past its window.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/decisions.md

@@ -13,6 +13,8 @@ Short record of why things are the way they are, so they don't get undone by acc
 - **Sections are transforms of A**, not new patterns. The phrase hangs together.
 - **Drift is continuous overlapping layers**, not steps. Wide knob spans used to do little. Drift adds displacement and weirdness at the top end.
 - **AMENIZER keeps its own feel.** Its humanising and chops are tuned so that DRIFT past halfway isn't too extreme. The generic layers come in later and at half strength.
+- **Kit and keys are split (2026-10-11).** One seed drives both through their own generator (KIT GEN, KEYS GEN). The keys-only choices (progression, scale, motif) moved into the keys half so ROLL KEYS renews the harmony too. Every seed changed sound; vectors regenerated. ENERGY, DRIFT, bar length, form and swing stay shared, and bass may still lock to the kicks.
+- **303 slides are overlaps only.** No portamento CCs: the synth channel is shared and poly, so a CC would bend every voice.
 - **ROOT and SCALE are global and sticky (2026-10-11).** They survive SEED, ROLL and slot loads, so a seed can be fitted to an existing idea. AUTO lets the seed pick from all 21 scales, which changed every seed's sound (vectors regenerated). Slots don't store the key.
 - **Integer-only engine** with a seeded RNG. This makes it deterministic and portable, and testable by golden vectors.