step_seq: the shared step-sequencer engine, its notebook, and the rhythm-section book chapters

[tap]

The kernel half of the coordinated phase 3 both plans/tap.808.md §6 and plans/tap.303.md §6 deferred to (design of record: plans/tap.seq.md in TapTools-Max, author-approved 2026-07-18), plus the verification notebook and six book chapters.

The engine — include/taptools/step_seq.h

One phase-clocked step engine (taptools::seq) with two thin emitters speaking the shipped voice contracts verbatim:

• Clocking: the caller feeds a phasor~-style ramp, 0..1 per pattern cycle; the engine derives the step as floor(phase × length) with swing warping the odd-step starts, sample-accurate entries, stateless against phase (jump/scrub/reverse all follow). Rows off one ramp are drift-free by construction; different lengths are polymeter.
• trigger_row (tap.808.seq~): amplitude-as-accent impulses on the 4–14 V bus mapping — plain 0.01 = the un-accented 4 V base, accented 0.5 = accent knob (VR3) at noon; pulse_ms widening for envelope consumers.
• note_row (tap.303.seq~): the pitch + gate pair at 1.0/2.0 accent amplitudes, gate duty 0.5 (Open303 AcidPattern::stepLength), and slide as gate-hold across the boundary — chained slides and the across-the-wrap slide included. Slide flag on the target step per the package note convention; the hardware's source-note storage is a documented divergence.
• 16 pattern slots with store/recall quantized to cycle|step|now; the armed swap re-derives the step against the new grid on the boundary sample.

19 new Catch2 scenarios (suite 129/129 green), including a pairing test that drives the real tb303_voice.h through the wrapper loop and asserts slid steps glide without retriggering.

The notebook — notebooks/step_seq.ipynb

Executed and asserted, house pattern: the shipping kernel driven through the C ABI (extended with taptools_seqtrig/taptools_seqnote and a minimal taptools_kick; TriggerRow/NoteRow/Kick added to taptools_py.py). Six sections: the analytic grid (≤ 1 sample), the swing warp (odd delay = swing/2), the trigger-bus levels, the 303 line signals — including the full-step hold on a slide source step, a case the isolated-step Catch2 scenario didn't exhibit — four bars of acid + kick rendered from the real voices off one ramp (embedded audio), and cycle-quantized recall swapping exactly on the wrap sample.

The book — Part V + Part VI additions

• Part V — The rhythm section: two field-guide chapters, The acid machine and The drum machine, every number sourced from the executed notebooks or the kernel suite.
• Part VI — machine chapters: Seventeen, not four (diode_ladder.h), The couplings are the instrument (tb303_voice.h), One network, eight voices (the tr808_* headers), and Time as a function of phase (step_seq.h).

CI / merge order

build and Tap House Style are green on the branch head. Merge this before tap/TapTools-Max#52 — the package PR pins this branch's head as the submodules/taptools submodule.

🤖 Generated with Claude Code

https://claude.ai/code/session_01JZivyxyBdHYd8sVf8AdUbN