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. Usage-detection (pS-usage, 2026-07-28): new pure module sample_usage + REAPER-facing shell usage_scan implement the instance-usage wire (rsusage_<instanceGuid> per-instance ext-state keys); each live ReaSampler 9000 instance publishes the captures it holds (from its SampleRefs) at reloadInstrument time; the extension reads every usage record at prune-scan time, liveness-folds against the live FX enumeration, and unions the surviving held paths into the prune's referenced set — so a capture held by any live instance can never be an orphan and BANK_PRUNE_FOLDER can never delete it; prune_reconcile gains mergeReferenced; persist's PruneReport gains abortedUnreadableUsage + offendingUsageKeys; dry-run / orphan-set / reclaim each independently abort (delete nothing) on unreadable usage; actions halts and prints offending keys; reaper_bridge gains writeUsageExtState (prefix-guarded — refuses non-rsusage_ keys); ComponentState bumped v10→v11 (instanceGuid field; pre-v11 blobs mint guid on first publish); new sample_usage_tests build target (pure, no REAPER/DAW).

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). The sample_usage_tests executable target runs the pure unit tests for sample_usage (no REAPER, no DAW).

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, and index-only move/copy/remove of a sample between banks. The JSON round-trip lives in the sibling bank_book_json TU (Q-W5 split; serialize/deserialize via a private static nameKey seam) — one model, one codec, same public surface.
• 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 #ifdefs in the shells.
• wav_codec — chunk walker + layout parse + float32 build + size-field patch + content hashes; the single pure RIFF/WAV owner. (wav_trim is now a transitional forwarding alias onto wav_codec, kept only so the Q-W2v TUs it feeds compile untouched; retire it once that wave lands.)
• 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. Gains mergeReferenced(bankRefs, liveInstanceHeldPaths) (pS-usage) — unions live instance holds into the prune referenced-set so the pure orphan computation includes them.
• 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.
• sample_usage — instance-usage wire: UsageRecord, planUsagePublish (fresh/heal/clean-replace/union/remint publish plan), foldUsageRecords/usageHeldPaths (liveness fold — protect-all when records exist but no instance is live; abort→protect-all on unreadable record), identityMatches (ReaSampler 9000 FX identity). REAPER-free, unit-tested. The mirror of assignment_request on the instrument→extension direction: the wire format and the two safety-critical decisions (what to write on publish, which records count at prune time) are pure so they are provable without a DAW.

REAPER-facing shells:

• capture — two CONCRETE backends with deliberately different lifecycles (no shared interface — the former ICaptureBackend was deleted in Q-W3, T4-26: one deriver, zero polymorphic call sites): OfflineRenderBackend (deterministic default, synchronous) and RealtimeRecordBackend (async begin/tick/abort). 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.
• shell/persist (session / ext_state_io / prune_fs) — the persist seam, split by responsibility (Q-W5; the former persist.cpp god-TU and its persist.h compatibility umbrella are both retired — callers include shell/persist/session.h / ext_state_io.h directly). session owns the ReaSamplerSession lifecycle: the poll identity-transition detection (load / Save-As / forked sibling / recycled pointer) and the projectconfig-driven deferred undo/redo reload. ext_state_io owns project ext state (SetProjExtState/GetProjExtState, namespace "reasampler") ↔ BankBook JSON, ViewModeModel JSON, TailSetting JSON, OwnedManifest JSON, the writing-version stamp, GUID minting, and bank-folder relocation. prune_fs hosts the prune dry-run / full-set orphan queries (supplying referencedPaths() + owned().paths() to the prune_reconcile pure core) and is the single file-deletion authority over user files in the bank folder (deleteOrphanFile via SHFileOperationW); nothing else in the system deletes bank-folder bytes. pS-usage: the prune scan unions instance usage via usage_scan; PruneReport carries abortedUnreadableUsage + offendingUsageKeys; dry-run / orphan-set / reclaim each independently abort (delete nothing) when usage state is unreadable.
• usage_scan — extension-side prune-scan shell (pS-usage): at prune-scan time, enumerates every rsusage_* ext-state key, decodes each sample_usage wire record, enumerates every ReaSampler 9000 FX instance across all tracks + master / normal + record chains / containers (recursive) / take FX, and folds with sample_usage::foldUsageRecords / usageHeldPaths to produce the set of held paths — or abortPrune when any record is unreadable (fail-safe: an unreadable record may protect anything, so the prune halts). Feeds prune_reconcile::mergeReferenced. Read-only: writes no ext-state.
• 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.
• shell/actions (action_registry / design_view_actions / bank_actions / prune_action) — the bindable action families, all routed via the command_id/gaccel/hookcommand contract. action_registry owns the shared registration plumbing (interned channel-qualified id strings; register and mirror-unregister present the identical pointer) and the Q-W6 registration TABLE: main.cpp's own family (capture scopes, panel toggle, insert, batch, realtime, recapture, version) is one ActionTableRow array — suffix, phrase, flat function-pointer handler — that registration, hookcommand dispatch, and the unload mirror-unregister all iterate, so adding an action touches the table only (OCP). Bank mutations flow through the promptless shell/bank_ops verbs (bankOp* + persistBankOp, taking ReaSamplerSession&), which the panel menus and bank_actions consume as thin UX skins. 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 (prune_action, BANK_PRUNE_FOLDER) is the ONLY file-deletion action in the system; it opens no undo point (file deletion is not REAPER-undoable). pS-usage: BANK_PRUNE_FOLDER halts on abortedUnreadableUsage and prints the offending rsusage_* key names with clear instructions.

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. pS-usage: gains writeUsageExtState (prefix-guarded — accepts only rsusage_-prefixed keys, refuses all others) so the processor can publish usage without weakening the read-only-bank invariant.
• 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. pS-usage: publishes instance usage (held SampleRefs paths) to rsusage_<instanceGuid> at the tail of reloadInstrument (off audio thread) via reaper_bridge::writeUsageExtState; ComponentState bumped v10→v11 (instanceGuid field); pre-v11 blobs mint guid on first publish.
• 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.