reasampler/CLAUDE.md

# CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

## Repo identity and current state

**ReaSampler** is a per-project audio sample-bank capture tool that builds two artifacts: the REAPER extension (`reaper_reasampler`) and **ReaSampler 9000**, a Windows-only VST3 sampler instrument (`reasampler_9000.vst3`, `src/vst/`, second CMake target `reasampler_vst`, gated on the vendored `vendor/vst3sdk` submodule slice). The pure-testable-core / REAPER-facing-shell discipline is preserved throughout. CONTEXT.md is the authoritative spec — settled decisions, invariants, guardrails, and not-yet-built specs; it is large, so locate the relevant phase section by grepping its headings and read only that section with an offset rather than reading it whole. Build detail for landed phases lives in CONTEXT-ARCHIVE.md. Every REAPER API name cited there is correct-by-intent; verify argument order, types, and flag values against `vendor/reaper-sdk/sdk/reaper_plugin_functions.h` before use. A post-S-VIEW DAW-fix pass has landed (all 52 suite tests green): envelope nodes fully editable in both modes (every Gate stage A/H/D/S/R + Trigger zero-fade-out node, param-domain schematic scaling, 8 px min node separation, all nodes clamped in-canvas); gap-free per-column waveform render (`columnMinMax` homed in `peaks`, `waveformColumnCount` in `component_geometry`, shared via `drawWaveform`); `param_slider` `Knob` primitive (7→5 o'clock arc, needle, vertical-drag); zone-bleed fix 3a (`reconcileSingleCaptureZones` in `sample_map`). The voice-system redesign is also landed: `sampler_core` gains user-parameterized voice count (1–32, default 16), `VoiceMode` Poly/Mono (last-note held-note stack, `MonoTrigger` retrigger/legato toggle), an isolated `PreviewCard` (dedicated preview voice outside the MIDI pool — never steals from/into it; unity-Preserve zero-latency bypass scoped to it), and two-tier panic (CC 123 = release, CC 120 = immediate hard-stop incl. Trigger one-shots); processor sums the preview card alongside the engine + drain, `retireIdleDrain()` retires fully-idle drain snapshots, and voice-param edits rebuild from the already-decoded PCM (no bank re-read/WAV re-decode) via the drain-slot swap; `ComponentState` envelope bumped v6→v7 (voiceCount/voiceMode/monoTrigger bytes; pre-v7 blobs lift to 16/Poly/Retrigger). **FB1 Sample-view recomposition (r11) has also landed** (suite 55/55 green): all linear sliders replaced by radial **knobs** in a fenced **knob deck** (groups: AMP ENVELOPE / PITCH / PITCH ENV / VOICE / MASTER); mode toggles are compact in the caption row, not full-width; the **hero waveform runs full-width** (elastic band, 840×620 default preserved); the inline velocity-curve box is replaced by a **28×28 curve preview button → centered popup** with right-click node delete; voice-band controls (count / Poly-Mono / Retrig-Legato) are placed in the VOICE deck group; a **post-mixer per-sample-ramped master gain** (−∞…+24 dB, no zipper) is placed in the MASTER deck group, persisted as `masterGainLinear` — `ComponentState` envelope bumped v7→v8 (pre-v8 blobs lift to unity gain). Three new pure `src/vst/` modules landed: `knob_deck` (group-box + caption-row + knob-cell geometry, deterministic wrap, hit-test), `curve_popup` (sheet/close/box geometry + outside-sheet dismissal test), `master_gain` (dB↔linear taper math, −∞…+24 dB). **FB2 Zone-panel parity (r11, 2026-07-28) has also landed** (suite 55/55 green): the Zone param panel now uses the same knob deck + curve-preview-button/popup grammar as the Sample face — one control grammar across both surfaces of the one per-zone storage site; Zone-authoring affordances (+Add Zone / Delete, the piano-key strip, Low/High/Root legend) are preserved; VOICE and MASTER groups remain Sample-only (per-instance). `param_slider`'s linear slider rows are retired on the Zone panel (the FA4 `Knob` primitive is now the only live consumer of that half of `param_slider`). **This completes the r11 editor recomposition (Wave B / Phase S editor redesign).** A **GA post-launch DAW-fix pass** has also landed (suite 55/55 green): `pitch_shift` rewritten from dual-tap OLA (anti-phase cancellation → spectral garbage on repitched notes) to **correlation-aligned SOLA splices** with a ratio-scaled raised-cosine fade (clean pitch shift past +24 st); `Voice::start` applies a **bounded blend** (`out*(1-w) + ref*w`, w decaying from 1.0) at takeover boundaries — mono retrig/fallback, poly at-cap steal, and preview re-trigger — superseding the earlier `(1-amp)` envelope-complement gate that zeroed the compensation on Trigger/zero-attack restarts; the output bus is now **permanently stereo** (`ChannelMode` is decode-only; the dynamic mono↔stereo bus renegotiation is deleted) with channel mode **auto-defaulting from the loaded capture** via new `ComponentState` **v9** (`channelModeExplicit` flag) + a pure `channelModeFor` helper; `SetCapture` moved to drag-arm in `bank_panel` so a first straight-out drag arms correctly; and the Design/Arrange mode-toggle action now calls `bankPanelInvalidate()` so the panel footer reflects the new mode without requiring a button click. **Preview via real MIDI note path (pS, 2026-07-28):** the dedicated `PreviewCard` is RETIRED; preview now injects a synthetic note-on at the loaded capture's root note into the main `VoiceEngine` (same path host MIDI uses), so it obeys polyphony/mono/voice-stealing/envelopes; the processor no longer sums a separate preview voice; the unity-Varispeed-bypass demotion (GA2 primed shifter speaks on frame 0 anyway) is removed. **Self-contained playback (pS, 2026-07-28):** `ComponentState` bumped v9→**v10** with a `SampleRefs` table — per referenced sample, the instance owns a project-relative path + decode intrinsics (root, loop, channels, displayName); `reloadInstrument` decodes directly from `SampleRefs`, bank-free (plays with the extension absent); the bank/bridge is now a browser source (loading a capture copies its reference in); the reopen-heal timer + poll-to-play apparatus are removed; pre-v10 blobs lift to empty refs and re-save self-contained.

## One-time submodule setup

    git submodule update --init

Vendors three submodules (see `.gitmodules`):
- `vendor/reaper-sdk` — `sdk/reaper_plugin.h`, `sdk/reaper_plugin_functions.h`, SWELL headers
- `vendor/WDL` — WDL utilities and the SWELL cross-platform Win32 layer
- `vendor/vst3sdk` — Steinberg VST3 SDK (Windows-only; requires a nested init after the top-level init):

      git submodule update --init vendor/vst3sdk
      cd vendor/vst3sdk && git submodule update --init pluginterfaces base public.sdk

  The VST3 target (`reasampler_vst`) is gated on `EXISTS .../pluginfactory.cpp` — configure quietly omits it if the slice is absent.

## Build and test

    cmake -B build -S .
    cmake --build build
    ctest --test-dir build

Every pure module has a corresponding `<module>_tests` executable target that runs without REAPER or a DAW. `CMakeLists.txt` is the authoritative target list. The two loadable-module targets are `reaper_reasampler` (the REAPER extension `.dll`/`.dylib`/`.so`) and `reasampler_vst` (the VST3 instrument; Windows-only, omitted if the `vendor/vst3sdk` slice is absent).

### Beta channel build

To build the fully isolated beta binary (`reaper_reasampler_beta`), pass the channel flag at configure time:

    cmake -B build-beta -S . -DREASAMPLER_CHANNEL=beta
    cmake --build build-beta

The flag threads through `configure_file` → `version_generated.h` and fans out via `app_version` into the binary name, ext-state namespace (`"reasampler_beta"`), command-id prefix (`CEREBELLUM_REASAMPLER_BETA_`), action-name prefix (`"ReaSampler beta: "`), dock ident, and version display (the configured version string with a `-beta` suffix appended). The default build (no flag) is byte-identical to the stable identity.

The VST3 target forks identically: `REASAMPLER_CHANNEL=beta` produces `reasampler_9000_beta.vst3`; the default produces `reasampler_9000.vst3`. The beta VST pairs **only** with the beta extension — each channel carries its own per-channel VST3 class UID, preventing a saved instance from rebinding across channels.

### macOS / Linux: SWELL dialog resources

`src/resource.rc` must be pre-processed by SWELL's resgen once per platform:

    php vendor/WDL/WDL/swell/swell_resgen.php src/resource.rc   # macOS; Linux reuses the output

Add the generated file to the appropriate `APPLE` / Linux `target_sources` block in CMakeLists.txt. The SWS extension build is the canonical reference for this step.

### Install / reload

There is no hot-reload. Copy the built binary into REAPER's `UserPlugins/` folder (Options → Show REAPER resource path) and restart REAPER. Extensions load at startup only.

## Architecture: the load-bearing split

**Pure core (no REAPER types, unit-testable outside the DAW):**
- `bank_model` — `Sample` metadata struct + `BankIndex` (add/remove/query/tier/dedup-by-hash + JSON round-trip). Test it hard — it is the heart.
- `peaks` — waveform min/max bin computation from raw PCM; does not depend on REAPER's peak API.
- `view_mode_model` — Design View mode system: mode registry, GUID-keyed membership, folder-tree-aware visibility derivation, snapshot-based park/restore planner, JSON round-trip.
- `view_tree` — pure `I_FOLDERDEPTH`→FolderTree helper for the Design View shell.
- `bank_grid` — REAPER-free grid layout, selection, keyboard-nav, and thumbnail-cache-key logic for the docked bank panel.
- `tab_strip` — REAPER-free scrollable tab-strip layout + hit-test for the named-banks strip.
- `mode_switch` — REAPER-free segment layout + hit-test for the bank_panel's Design View mode switch.
- `bank_book` — multi-bank registry: an ordered set of banks each wrapping a `BankIndex`. **Pool privileges (un-deletable/un-renamable/un-evacuable, never zero banks) enforced in-model.** Owns create/rename/reorder/delete of named banks, active-bank id, index-only move/copy/remove of a sample between banks, and JSON round-trip.
- `owned_manifest` — the set of project-relative files the capture path itself created, persisted under the `"owned_files"` ext-state key, so the prune path can distinguish the bank system's own orphans from hand-dropped files.
- `app_version` — REAPER-free version/channel identity: CMake-sourced semver constant, ext-state stamp value, and the full set of channel-derived identity accessors. All channel strings derive from one `REASAMPLER_CHANNEL_IS_BETA` bit; no scattered `#ifdef`s in the shells.
- `wav_trim` — 32-bit-float WAV parse + header-aware truncate plan for the realtime tail's PCM decay-scan trim.
- `provenance` — capture-recipe fingerprint: build/encode/compare a `rsprov1` fingerprint of scope, range, tail, rate/channels, track GUIDs, and FX-chain identity. **A thin reproducibility fingerprint — NOT a serialized chain to restore.**
- `prune_reconcile` — pure prune core: `pruneOrphans(present, referenced, owned)` computes `(owned ∩ present) − referenced`; the safety-critical "which files are orphans" decision, filesystem-free and hard-tested before any I/O exists.
- `prune_button` — pure layout/hit-test for the `bank_panel` footer Prune button.
- `batch_capture` — pure batch-capture planner: maps source ranges to capture units and aggregates results.
- `action_buttons` — pure action-button strip layout/hit-test.
- `drag_out` — pure OS drag-out module: gesture-boundary decision and path-list assembly. The `InstrumentDrop` gesture signals that the shell should execute an instrument-drop rather than a file-copy drag.
- `theme` — pure palette module: role→color mapping, REAPER-grey neutral ladder + three-accent pastel system, WCAG contrast-floor helpers.
- `component_geometry` — pure button/slider/list-row geometry + hover hit-test helpers.
- `action_bar` — pure task-grouped action-bar layout/hit-test: clusters (Capture / Placement / Maintenance / Tagging / Switching).
- `footer_bar` — pure footer layout/hit-test: `[Arrange|Design]` mode-toggle geometry, Tail button, and Prune placement.
- `overflow_menu` — pure overflow-menu-button geometry/reserve/hit-test for the top-toolbar More (⋯) button.
- `mode_enable` — pure opposite-mode enablement predicate: given the active mode, computes per-button live/disabled state for the four Item/Track × Arrange/Design tag buttons.
- `tooltip` — pure tooltip placement + prefix-strip: strips the `ReaSampler:` display prefix from the registered action phrase; width clamped to the client rect.
- `card_drag` — pure drag-gesture precedence + slot hit-test: leave-client → OS drag-out; other-bank → move/copy; same-bank → reorder / Alt-over-occupied → replace.
- `card_meta` — pure card-metadata formatters: bars.beats.subdivisions and seconds.milliseconds; blank when the sample is unstamped.
- `instrument_drop` — pure FX-drop payload builder: constructs a Steinberg-format `.vstpreset` image (channel-active class ID + the instrument's own component state, capture pre-selected) the shell applies via `TrackFX_SetPreset`; owns the `infoNamesFxHotspot` prefix classifier for `GetThingFromPoint` tokens. All-or-nothing contract — caller rolls back via `TrackFX_Delete` on any failure.
- `assignment_request` — pure ingest-assign wire: typed request record carrying the drop payload from the `ingest` shell through to the VST3 bridge.

**REAPER-facing shells:**
- `capture` — `ICaptureBackend` interface; `OfflineRenderBackend` (deterministic default) and `RealtimeRecordBackend`. Input: `CaptureRequest`. Output: finished file + populated `Sample` handed to `bank_model`.
- `insert` — placement via `InsertMedia`. **Conform-to-project-tempo is an explicit opt-in flag, never silent stretching.**
- `bank_panel` — docked LICE-drawn grid with three-zone layout: top toolbar (Capture → Maintenance → Placement via `action_bar`, short labels, More (⋯) overflow menu via `overflow_menu`), bottom toolbar (four opposite-mode tag buttons + Show Both), and footer (`[Arrange|Design]` toggle, Tail button, Prune via `footer_bar`). Grid renders in sparse slot order with gap cells, drop dispatch, metadata overlay, and selection via `accent/tertiary` purple border. Draws through the L1 kit by palette role; OS drag-out via `drag_out` + `drag_out_win`.
- `persist` — project ext state (`SetProjExtState`/`GetProjExtState`, namespace `"reasampler"`) ↔ `BankBook` JSON, `ViewModeModel` JSON, `TailSetting` JSON, `OwnedManifest` JSON, and writing-version stamp. A `projectconfig` hook triggers a deferred session reload on undo/redo. Hosts the prune dry-run and full-set orphan queries; supplies `referencedPaths()` + `owned().paths()` to the `prune_reconcile` pure core.
- `view` — Design View shell: snapshots flag values before parking, drives hide + CPU-park on inactive-mode leaves (`B_SHOWINTCP`/`B_SHOWINMIXER`/`B_MAINSEND`/`I_FXEN` + per-FX offline), restores from snapshot. **Never touches master or `B_MUTE`/`I_SOLO`.**
- `track_guid` — shared `MediaTrack*` → canonical GUID-string formatter; single source of truth for membership keys.
- `provenance_shell` — FX-chain identity queries via `TrackFX_*`/`TakeFX_*` APIs; feeds the pure `provenance` fingerprint builder. Stamps `Sample.provenance` on capture; ambiguous/mixed cases record nothing conservatively.
- `drag_out_win` — OS drag-out shell: Windows OLE `DoDragDrop`/`CF_HDROP`, copy-only (`DROPEFFECT_MOVE` not offered); macOS/Linux via `SWELL_InitiateDragDropOfFileList`.
- `ingest` — ingest-through-the-bank shell on the EXTENSION side: three surfaces — (1) arrange capture→bank→assign (bindable action), (2) Media-Explorer import→bank→instrument on the selected track, (3) file drop onto the bank panel→bank only. Only surface (1) writes the `assignment_request` ext-state wire. **ingest NEVER inserts a timeline item.**
- `instrument_drop_win` — FX-button drop shell: resolves a screen point to a track + FX-surface hotspot, then adds a ReaSampler 9000 instance and applies the dragged capture's state via a transient `.vstpreset` + `TrackFX_SetPreset` (the former `TrackFX_SetNamedConfigParm` "vst_chunk" write was silently unappliable for VST3). Exposes `loadInstrumentOntoTrack` (inner half, no own undo block) and `performInstrumentDrop` (wraps in its own undo block). **Never captures, never writes the bank, never inserts a timeline item.**
- `draw_kit` — shared LICE draw shell: `fillSurface`, `drawButton`/`drawSlider`/`drawListRow`/`drawWaveform`, cached-font `text()`, full interaction-state model, double-buffer preserved. Consumes `theme` + `component_geometry`.
- `actions` — registers the capture/placement/slot, Design View, multi-bank, and prune action families; routes each via the `command_id`/`gaccel`/`hookcommand` contract. **Every bank index verb wraps its mutation in a batched REAPER undo point (`Undo_BeginBlock2`/`EndBlock2`, `UNDO_STATE_MISCCFG`) so one bank operation is one Ctrl-Z.** The prune action (`BANK_PRUNE_FOLDER`) is **the ONLY file-deletion authority in the system**; it opens no undo point (file deletion is not REAPER-undoable).

**VST3 instrument (`src/vst/`) — pure core:**
- `sampler_core` — polyphonic voice engine with bounded stealing, user-parameterized voice count (1–32, default 16), `VoiceMode` Poly/Mono (last-note held-note stack, `MonoTrigger` Retrigger/Legato toggle), two-tier panic (CC 123 = all-notes-off release, CC 120 = immediate hard-stop including Trigger one-shots); per-zone `ZonePlayParams` (Gate/Trigger, AHDSR, pitch engine Varispeed/Preserve, AD pitch mod envelope), repitch/interpolation with loop-point-aware sustain. Preview injects a synthetic note-on at the loaded capture's root note into the main `VoiceEngine` — no dedicated `PreviewCard`; preview obeys polyphony/mono/voice-stealing/envelopes.
- `sample_map` — zone payload: zones keyed by note range. **Wall-clock times stored as rate-free SECONDS, resolved against the live project rate — NO hardcoded sample rates in `src/`** (Daniel's standing ruling, load-bearing). JSON round-trip.
- `pitch_shift` — hand-rolled **correlation-aligned SOLA** (splice-overlap-add) pitch shifter for the Preserve playback mode: one active read tap chases the write head at the shift ratio; each splice jump is refined by a cross-correlation search so the new read point is waveform-aligned, then old and new taps are crossfaded (raised-cosine, amplitude-complementary). Replaces the prior dual-tap OLA whose fixed half-window tap offset caused anti-phase cancellation on many source frequencies. **GA2:** ring buffer **primed with the actual upcoming source** at note-on (was zero-filled) → gap-free frame-0 onset, ~25 ms Preserve onset latency eliminated (Preserve now speaks on frame 0, matching Varispeed), and real-content-bounded tail (last-window tail-truncation gone). No third-party dependencies; RT-discipline: no allocation in `process()`.
- `bank_sync` — generation change-detection + assignment-request consume: owns the yes/no decision logic so the rules are provable without a host. The processor shell owns cadence and side effects.
- `bridge_marshal` — pure marshalling helper for the REAPER VST-host bridge read: interprets the `GetProjExtState` int return against its filled buffer.
- `editor_geometry` — VST3 editor layout: defines the shared `Rect` type + `contains()` hit-test; provides `EditorLayout` and `layoutEditor(w,h)`.
- `keyboard_strip` — piano-keyboard strip: MIDI-note→key rect mapping, black/white key layout, hit-test, zone highlight overlay geometry.
- `waveform_view` — waveform/marker geometry: maps frame span linearly across a rect; generic named draggable markers with drag-delta resolver, clamp, and zero-crossing snap.
- `capture_browser` — capture browser: card-grid layout + bank-filter tab strip geometry and hit-test; knows only counts and rects, draws nothing.
- `browser_scroll` — scroll + type-to-filter layered over `capture_browser`: vertical scroll offset, scrollbar thumb, thumb-drag mapping, and name-substring search.
- `note_entry` — parses a raw string into a clamped MIDI note [0,127]; accepts plain decimal integers or note names (C4==60, DAW convention).
- `param_slider` — parameter control-panel: vertical stack of TOGGLE (two-segment selector) and SLIDER (horizontal track) rows; maps normalized value to/from handle pixel.
- `trigger_seam` — pure Trigger frames↔fraction converter: owns the shared formula for converting between engine source-frame fade counts and the overlay's fractional representation, threading `startFrame` correctly through pack and unpack directions.
- `velocity_curve` — pure velocity→amp transfer curve: `VelocityCurve` evaluated by a Fritsch–Carlson monotone cubic Hermite spline (no overshoot outside [0,1]). `eval(velocity)` called once per note-on. `flat()` default (y=1, every velocity→unity) replaces the prior fixed `velocity/127` path — a deliberate non-back-compat behavior change (Daniel-approved).
- `embed_strip` — compact single-row control layout for embed mode in the track FX chain.
- `knob_deck` — pure knob-deck layout + hit-test (FB1): group-box / caption-row / compact-toggle / knob-cell geometry, deterministic whole-group wrap, `DeckLayout` / `DeckHit`. Mirror of `action_bar`/`param_slider`; no LICE or REAPER types.
- `curve_popup` — pure curve-popup geometry + dismissal test (FB1): centered sheet over the Sample face — width/height clamps, title row, Close button rect, curve-box rect, outside-sheet dismissal test. Mirror of `overflow_menu`; no LICE or REAPER types.
- `master_gain` — pure dB↔linear taper math (FB1): normalized [0,1] ↔ dB ↔ linear for the post-mixer master gain control (−∞…+24 dB, norm 0 = true silence, unity ≈ 0.714). Shared by the editor knob and the processor multiply so the needle, persisted value, and audio multiply cannot drift.
- `reasampler_uid.h` — SDK-free header owning the FOREVER-FROZEN VST3 class-UID integer macros (stable + beta pairs, `REASAMPLER_PROC_UID_*` / `REASAMPLER_PROC_UID_BETA_*`) and the `REASAMPLER_ACTIVE_UID_*` channel-selector macros. Split out of `reasampler_vst.h` so the pure extension side (`instrument_drop`) can derive the `.vstpreset` class-ID hex string without pulling in the VST3 SDK. Both `reasampler_vst.h` (runtime `FUID`) and `instrument_drop` (preset hex string) source from this single header — the binary identity and the preset-file identity cannot diverge.

**VST3 instrument (`src/vst/`) — shells:**
- `reaper_bridge` — READ-ONLY bank consumer: receives bank snapshots from the extension and exposes them as a read-only view. **Never writes to the extension's bank** — this is a load-bearing invariant; no mutation path exists in this module.
- `reasampler_processor` — VST3 `SingleComponentEffect` shell: declares event-input bus + **permanently stereo** output (GA fix: dynamic mono↔stereo bus renegotiation deleted; `ChannelMode` is now decode-only), marshals MIDI note-on/off into the VoiceEngine, renders audio; owns off-audio-thread `reloadInstrument` + atomic pointer swap so `process()` does no allocation, no file I/O, no bridge calls. **Self-contained playback (pS):** `ComponentState` v10 adds a `SampleRefs` table — per referenced sample, a project-relative path + decode intrinsics (root, loop, channels, displayName); `reloadInstrument` decodes directly from `SampleRefs`, bank-free (plays with the extension absent). The bank/bridge is a browser source: loading a capture copies its reference in; the reopen-heal timer + poll-to-play apparatus are removed. `retireIdleDrain()` retires fully-idle drain snapshots on the UI-timer cadence. Voice-param edits (`setVoiceCount`/`setVoiceMode`/`setMonoTrigger`) rebuild the engine from the already-decoded keymap via the drain-slot swap — no bank re-read, no WAV re-decode, no audible cut to ringing tails. **FB1:** applies the post-mixer `masterGainLinear` (from `ComponentState` v8) as a per-sample ramp over the summed output — no zipper noise. **GA v9:** `channelModeExplicit_` flag persisted; `channelModeFor()` auto-defaults the mode from the loaded capture's channel count when the flag is not set. **pS:** `ComponentState` bumped v9→v10 (`SampleRefs` table); pre-v10 blobs lift to empty refs and re-save self-contained.
- `reasampler_editor` — VST3 `IPlugView` LICE editor shell: hosts a LICE-drawn child window; default face is the capture browser, then single-capture setup, with opt-in zones panel. Drop-onto-editor ingest is NOT shipped (deferred).
- `reasampler_embed` — implements `IReaperUIEmbedInterface` so the instrument draws inline in the TCP/MCP without a plugin-owned HWND; delegates layout/hit-test to `embed_strip`.
- `vst_entry` — VST3 entry point: `GetPluginFactory` export, class registration, channel-forked class UIDs.

## REAPER extension contract (src/main.cpp)

- Exactly **one** translation unit defines `REAPERAPI_IMPLEMENT` — that is `main.cpp`. Every other `.cpp` includes `reaper_plugin_functions.h` without the define and gets `extern` declarations for the global API function pointers.
- REAPER dlopen()s any `reaper_*.dll|dylib|so` found in `UserPlugins/` and calls the `ReaperPluginEntry` export (produced by `REAPER_PLUGIN_ENTRYPOINT`). `rec->GetFunc` resolves API pointers; `rec->Register` plugs extension callbacks in.
- Action registration pattern (preserve this for all new actions):
  1. `rec->Register("command_id", (void*)"STABLE_FOREVER_STRING")` — mints a persistent command id. **Never change this string after shipping**; user keybindings key off it. Since Phase V (V4), ids and display names are composed via `channelCommandId(suffix)` and `channelActionName(phrase)` from `app_version` — the FOREVER-STABLE contract applies per channel (stable and beta each have their own permanent id family).
  2. `rec->Register("gaccel", &accel)` — puts the action in the Actions list.
  3. `rec->Register("hookcommand", ...)` — receives every action fired; claim only your own id, return `false` otherwise.
  4. On unload (`rec == nullptr`), mirror-unregister everything with the same strings prefixed by `'-'`.

## Product design docs

`docs/product/` holds the product-design reasoning behind each phase — the "why we chose this" that predates the spec. They are large and are cited by section from `CONTEXT.md` and `PLAN.md`; **grep for the cited section rather than reading a file whole**. `docs/cmake-cheatsheet.md` is a standalone build-system reference.

Files: `capture-tail.md`, `code-organization.md`, `design-view.md`, `midi-playback.md`, `multi-bank.md`, `provenance.md`, `removal-and-prune.md`, `versioning-and-release.md`, `visual-design-language.md`.

## The load-bearing principle

**Capture and placement are separate acts.** Capturing audio writes a file to the bank and adds an index entry. It **never** puts an item in the arrange view. Placement is a distinct, on-demand action (`insert` module / `InsertMedia`). Any code path that auto-inserts a capture into the timeline violates the purpose of the tool and **must be rejected in review**.

## Precision invariants — required before any feature ships

- **Null test:** a dry offline capture of a range, re-inserted at its source position, nulls to silence against the source. Ship as a verification action.
- **Bit-identical repeats:** identical offline capture requests produce identical files.
- **Non-destructive:** capture never mutates source items or tracks; the realtime backend's temp track is created and removed cleanly, and source routing is restored.
- **Exact bounds:** no rounding of the requested range; no added silence unless a tail is explicitly requested; channel count preserved (no silent stereo fold).
- **Relative paths only** in the persisted `BankIndex`.
- **Capture FX scope:** two scopes only — item = item/take FX only; track = item FX + the selected track's own track FX. There is no master scope (to capture the master, render a track instead). For both scopes, the out-of-scope chain (ancestors + master track, plus the item's own track for item scope) has its FX, gain, and pan/width/pan-law/mode neutralized to unity — the master track is bypassed as out-of-scope chain, not captured as a scope. Range (time selection or razor) is orthogonal.