diff --git a/.claude/hooks/session-start.sh b/.claude/hooks/session-start.sh
new file mode 100755
index 0000000..b7c2a49
--- /dev/null
+++ b/.claude/hooks/session-start.sh
@@ -0,0 +1,36 @@
+#!/bin/bash
+# Canonical Tap House SessionStart hook for Claude Code on the web.
+#
+# Fresh web-session containers clone the repo bare: no submodules, no
+# pre-commit hook installed — so `git commit` runs unformatted and the
+# clang-format CI gate fails on code a local clone would have fixed at commit
+# time. This hook closes that gap at session start:
+#
+#   1. init submodules recursively (kernels, SDKs, vendored test harnesses)
+#   2. install pre-commit and register the repo's canonical hook
+#      (.pre-commit-config.yaml — the Tap-wide pinned clang-format)
+#   3. warm the pinned clang-format binary so the first commit doesn't
+#      pay the download (the container snapshot caches it)
+#
+# Canonical copy: taphouse (distributed by scripts/sync.sh alongside
+# .clang-format / .clang-tidy / .pre-commit-config.yaml; drift-guarded where
+# present). Web-only; local clones are untouched.
+set -euo pipefail
+
+if [ "${CLAUDE_CODE_REMOTE:-}" != "true" ]; then
+    exit 0
+fi
+
+cd "$CLAUDE_PROJECT_DIR"
+
+echo "session-start: initializing submodules ..."
+git submodule update --init --recursive
+
+echo "session-start: installing pre-commit ..."
+if ! python3 -m pre_commit --version >/dev/null 2>&1; then
+    python3 -m pip install --quiet pre-commit
+fi
+python3 -m pre_commit install
+python3 -m pre_commit install-hooks
+
+echo "session-start: done."
diff --git a/.claude/settings.json b/.claude/settings.json
new file mode 100644
index 0000000..e06b033
--- /dev/null
+++ b/.claude/settings.json
@@ -0,0 +1,14 @@
+{
+  "hooks": {
+    "SessionStart": [
+      {
+        "hooks": [
+          {
+            "type": "command",
+            "command": "$CLAUDE_PROJECT_DIR/.claude/hooks/session-start.sh"
+          }
+        ]
+      }
+    ]
+  }
+}
diff --git a/.github/workflows/style.yml b/.github/workflows/style.yml
index ee11eaa..3006abb 100644
--- a/.github/workflows/style.yml
+++ b/.github/workflows/style.yml
@@ -8,9 +8,9 @@ on: [push, pull_request]
 jobs:
   drift:
     # Fails if this repo's .clang-format/.clang-tidy/STYLE.md diverge from TapHouse.
-    uses: tap/taphouse/.github/workflows/drift-check.yml@v4
+    uses: tap/taphouse/.github/workflows/drift-check.yml@v5
     with:
-      ref: v4
+      ref: v5
 
   clang-format:
     runs-on: ubuntu-latest
diff --git a/CLAUDE.md b/CLAUDE.md
new file mode 100644
index 0000000..0e60d41
--- /dev/null
+++ b/CLAUDE.md
@@ -0,0 +1,81 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## What this is
+
+**TapTools** (this repo, `tap/taptools`) — the portable DSP kernel library behind the
+[TapTools-Max](https://github.com/tap/TapTools-Max) package of Max/MSP externals: one
+self-contained header per object under `include/taptools/`, namespace `tap::tools`, plain C++20
+with the standard library only — no Max, no Min, no frameworks. The AmbiTap / AmbiTap-Max split:
+DSP lives and is tested *here*; the Max repo is thin wrappers plus a submodule pin of this repo.
+Shared low-level primitives (real FFT, YIN, PSOLA, phase vocoder) live one level further down in
+the [DspTap](https://github.com/tap/dsptap) submodule (`submodules/dsptap`, target `tap::dsp`) —
+general-purpose signal primitives go there; musical/object-level kernels stay here.
+
+## Layout
+
+- `include/taptools/` — one header per kernel (e.g. `tune.h`, `svf.h`, `grm_pitchaccum.h`);
+  `stft.h` is the shared overlap-add scaffold for the spectral kernels.
+- `submodules/dsptap/` — `tap::dsp` (fft/yin/psola/pvoc + vendored Ooura/CMSIS), pinned.
+- `tests/` — Catch2 (FetchContent), pure C++, no Max/min-api/mock kernel; runs via `ctest`.
+- `tools/capi/` + `notebooks/` — the verification layer: a C ABI over the same kernel headers the
+  externals compile, a ctypes bridge (`notebooks/taptools_py.py`), and *executed* verification
+  notebooks. `tools/` also holds render tools (e.g. `tr808_render`).
+- `book/` — *Tools on Tap* (mdbook), the field guide; `bench/` — benchmarks.
+
+## Kernel conventions (load-bearing)
+
+- **Shape:** a class in `tap::tools::<name>` with `prepare(sr)` (all allocation happens here),
+  per-sample `process(...)`, and setters that are allocation-free and safe while audio runs.
+  Worst-case geometry is bought at `prepare()` so runtime parameter changes never reallocate.
+- **No zippers:** parameters ride per-sample linear ramps or one-pole slews (see `grm_comb.h` /
+  `grm_pitchaccum.h` for the param_index + ramp house pattern).
+- **Provenance is documented.** Faithful ports keep magic constants and cite where they came from;
+  recreations cite papers/schematics. New DSP is implemented from published literature only —
+  an IP policy, not a citation habit.
+- **Honest limits in the header.** Known failure modes and material contracts (e.g. PSOLA wants
+  harmonic input) are stated where the next reader will look.
+
+## Style
+
+`STYLE.md` + `.clang-format` + `.clang-tidy` are the canonical Tap House copies (synced from
+taphouse; CI drift-checks them — never hand-edit). Run `pre-commit install` once per clone; on
+Claude Code web the checked-in SessionStart hook does it automatically. clang-tidy compiles with a
+clang front end — treat it as a second compiler, not a linter.
+
+## Build & test
+
+```sh
+git submodule update --init --recursive
+cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
+cmake --build build
+ctest --test-dir build --output-on-failure
+```
+
+Tests are Catch2 `SCENARIO`s named for the promise they pin. House patterns worth preserving:
+**oracle-based measurement** (drive the kernel with synthesized material and measure the *output*
+with an independently certified detector — `tap::dsp::yin` — rather than asserting internals; this
+is how the tune kernel's 5-cent period-lock bias was caught), and **material contracts** (test
+PSOLA-family code with sawtooth, not sine, per its documented contract).
+
+## Verification layer
+
+The notebooks drive the shipping C++ through `tools/capi` via ctypes — never Python
+re-implementations. They are committed executed; re-execute when behavior changes. When adding a
+kernel that notebooks (or other bindings) should reach, extend `tools/capi/taptools_capi.{h,cpp}`
+and `notebooks/taptools_py.py` alongside it.
+
+## The book
+
+`book/` is *Tools on Tap* (mdbook, `src/SUMMARY.md`, `create-missing = false` so SUMMARY entries
+must exist). One user-facing chapter per object family plus "The machine, file by file"
+appendices. The standing promise: **every performance claim is measured, not remembered** — cite
+the executed notebook cell or pinned test that carries each number. Chapter plans live as
+`book/PLAN-*.md` drafting records and stay after the chapters ship.
+
+## Release flow
+
+DSP changes land here (or in dsptap, then bump `submodules/dsptap` here); TapTools-Max then bumps
+its `submodules/taptools` pin. After a PR merges via rebase/squash, repoint any open consumer pins
+at the identical tree on `main` so they stay reachable after branch cleanup.
diff --git a/scripts/tidy.sh b/scripts/tidy.sh
new file mode 100755
index 0000000..45fc009
--- /dev/null
+++ b/scripts/tidy.sh
@@ -0,0 +1,77 @@
+#!/usr/bin/env bash
+# Local mirror of the CI clang-tidy gate (.github/workflows/style.yml): the
+# TapHouse .clang-tidy naming + mandatory-braces checks over this project's
+# own translation units. Run it before pushing.
+#
+# WHY THIS EXISTS (and is not a pre-commit hook): the pre-commit hook only
+# runs clang-FORMAT, which is cheap and context-free. clang-TIDY needs a
+# compile database (a configured CMake build) and compiles every TU to reason
+# about types — too slow and stateful for a per-commit hook, so CI keeps it as
+# its own gate. This script is the fast local equivalent of that gate.
+#
+# Usage:
+#   scripts/tidy.sh                       # sweep every project TU (full CI mirror)
+#   scripts/tidy.sh tests/test_foo.cpp …  # only the given TU(s) — fast, for a change
+#
+# Env:
+#   CLANG_TIDY=clang-tidy-18   # binary to use (default: clang-tidy-18, then clang-tidy)
+#   TIDY_BUILD=build-tidy      # compile-database build dir (kept separate from ./build)
+#   TIDY_RECONFIGURE=1         # force a cmake re-configure of the compile database
+set -euo pipefail
+
+repo_root="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+cd "$repo_root"
+
+# Prefer clang-tidy-18 — the version the CI gate installs and the .clang-tidy
+# checks are validated against; a different major version may disagree.
+tidy="${CLANG_TIDY:-}"
+if [ -z "$tidy" ]; then
+    if command -v clang-tidy-18 >/dev/null 2>&1; then
+        tidy=clang-tidy-18
+    elif command -v clang-tidy >/dev/null 2>&1; then
+        tidy=clang-tidy
+        echo "warning: clang-tidy-18 not found; using '$tidy'. CI pins v18 — results may differ." >&2
+    else
+        echo "error: no clang-tidy found. Install clang-tidy-18 (apt) or set CLANG_TIDY=..." >&2
+        exit 127
+    fi
+fi
+
+build="${TIDY_BUILD:-build-tidy}"
+
+# A compile database is what clang-tidy needs; reuse it across runs unless it is
+# missing or a reconfigure is forced. This does not touch your ./build dir.
+if [ "${TIDY_RECONFIGURE:-0}" = "1" ] || [ ! -f "$build/compile_commands.json" ]; then
+    echo "== configuring compile database in $build/ (one-time; reuses cached deps) =="
+    cmake -B "$build" -DCMAKE_EXPORT_COMPILE_COMMANDS=ON >/dev/null
+fi
+
+# File list: the given TUs, or — matching CI exactly — every project TU in the
+# database with third_party/ and fetched deps (_deps) excluded.
+if [ "$#" -gt 0 ]; then
+    files=("$@")
+else
+    mapfile -t files < <(python3 -c "
+import json
+for e in json.load(open('$build/compile_commands.json')):
+    f = e['file']
+    if 'third_party' not in f and '_deps' not in f:
+        print(f)")
+fi
+
+echo "== clang-tidy ($tidy) over ${#files[@]} file(s) =="
+fail=0
+for f in "${files[@]}"; do
+    out="$("$tidy" -p "$build" "$f" 2>/dev/null || true)"
+    if printf '%s\n' "$out" | grep -qE "warning:|error:"; then
+        printf '%s\n' "$out"
+        fail=1
+    fi
+done
+
+if [ "$fail" -eq 0 ]; then
+    echo "clang-tidy clean."
+else
+    echo "clang-tidy found violations (above); fix before pushing." >&2
+    exit 1
+fi