instrument: one VELOCITY deck for all three velocity curves, bipolar and off by default for pitch and filter

Payload v12 appends the new velocity->pitch curve and folds the retired filter velAmount into its now-bipolar curve, so pre-v12 projects reopen sounding identical. Preview button takes a drawn play triangle.

src/core/instrument/CLAUDE.md

@@ -243,10 +243,12 @@ anything for a trigger shape.
   reloads** via the instrument's own `ComponentState` (envelope-bumped), never via the
   extension's `persist` ext-state module (that would make it project-global rather than
   per-instance and leak an instrument concern into the extension's key space).
-- **Velocity curve** — the one non-back-compat surface in S-VIEW: an
-  already-saved instance with no stored curve now plays every velocity at unity under the
-  flat-default (Option A), not bit-identical to the old linear `velocity/127` mapping —
-  a deliberate, Daniel-approved behavior change (see `velocity_curve` in Modules).
+- **Velocity curves** — three of them (amp, pitch, filter), all per-instance, edited from ONE
+  deck group. The amp curve is the one non-back-compat surface in S-VIEW: an already-saved
+  instance with no stored curve now plays every velocity at unity under the flat-default
+  (Option A), not bit-identical to the old linear `velocity/127` mapping — a deliberate,
+  Daniel-approved behavior change. The pitch and filter curves are bipolar and off by default
+  (see `velocity_curve` in Modules).
 
 ## Modules
 
@@ -260,13 +262,13 @@ anything for a trigger shape.
   - `voice_engine.h` / `voice_engine.cpp` — `VoiceEngine`: note routing, bounded-stealing allocation, user-parameterized voice count (1–32, default 16), `VoiceMode` Poly/Mono (last-note held-note stack, `MonoTrigger` Retrigger/Legato), two-tier panic (CC 123 = all-notes-off release, CC 120 = immediate hard-stop including Trigger one-shots), and the block render loops. 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.
 - `engine/loop/` — the sustain loop's ONE validity/clamp fold (`resolveLoop`) plus its pre-seam crossfade geometry and the editor's default handle span; see `engine/loop/CLAUDE.md`. The voice folds it once at note-on; the crossfade weight is header-inline because it rides the per-sample read.
 - `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()`.
-- `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).
+- `velocity_curve` — the pure velocity transfer curve shared by all THREE destinations: `VelocityCurve` evaluated by a Fritsch–Carlson monotone cubic Hermite spline (no overshoot). `eval(velocity)` called once per note-on. It carries its own y `CurveDomain`: UNIPOLAR [0,1] is the amp's GAIN, defaulting to `flat()` (y=1, every velocity→unity — a deliberate non-back-compat replacement of the old fixed `velocity/127` path, Daniel-approved); BIPOLAR [−1,1] is the signed modulation depth for pitch and filter, defaulting to `zero()` so velocity modulates neither until a curve is drawn. A bipolar curve is BOTH the shape and the amount — there is no depth control behind it, which is why the filter's `velAmount` retired into it. eval is HOMOGENEOUS in y (scaling every knot by k scales the curve by k exactly); the codec's pre-v12 lift rests on that.
 - `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.
 
 ### `map/`
 
 - `sample_map` — the bank blob → selected capture resolve, the channel policy (downmix / dual-mono / L-R split), `InstrumentParams` (the ONE parameter set: root/loop/start overrides, keyTrack, velocity curve, `PlaySeconds`), the single override-beats-intrinsic fold (`resolveCapture`, shared by the bank and refs paths so they cannot drift), and the `SampleData` build. **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). Deliberately does NOT link the voice engine: the build's product is plain `SampleData`.
-- `component_state_io` (`core/instrument/map`) — the `ComponentState` envelope + params-payload binary codec (envelope v1…v11, params payload v1…v11), split out of `sample_map` (Q-W2v, T4-13 ≡ T2-07) so BOTH artifacts can link the codec without the extension pulling in the whole voice engine to serialize one preset blob — the extension's `instrument_drop` and the instrument's processor read/write the identical bytes, so the cross-artifact contract cannot drift. Payload v1…v7 are the RETIRED per-zone lists: still read, lifting by adopting zone one's capture + parameters (that first zone is what the old first-match resolve actually played, so it is also what supersedes the envelope's stored selection id). Payload v9 appends the per-voice filter tail; a v8 blob is a strict prefix of it and lifts to the off/neutral filter default. Every tail since is a strict suffix on the same discipline — v10 the staged curves, v11 the loop crossfade.
+- `component_state_io` (`core/instrument/map`) — the `ComponentState` envelope + params-payload binary codec (envelope v1…v11, params payload v1…v12), split out of `sample_map` (Q-W2v, T4-13 ≡ T2-07) so BOTH artifacts can link the codec without the extension pulling in the whole voice engine to serialize one preset blob — the extension's `instrument_drop` and the instrument's processor read/write the identical bytes, so the cross-artifact contract cannot drift. Payload v1…v7 are the RETIRED per-zone lists: still read, lifting by adopting zone one's capture + parameters (that first zone is what the old first-match resolve actually played, so it is also what supersedes the envelope's stored selection id). Payload v9 appends the per-voice filter tail; a v8 blob is a strict prefix of it and lifts to the off/neutral filter default. Every tail since is a strict suffix on the same discipline — v10 the staged curves, v11 the loop crossfade, v12 the velocity→pitch curve. v12 also RE-INTERPRETS two frozen slots inside the v9 filter tail (its velocity curve is now bipolar and self-scaling; the retired velAmount slot carries a constant 1.0) — same bytes, version-keyed meaning, with the pre-v12 fold documented in `component_state_io.h`.
 - `params_payload` — the PARAMS-PAYLOAD half of that codec, split from the envelope half on the axis the format already has: the payload carries its own version and grows independently, so the two version ladders are two responsibilities. An INTERNAL seam — the public entry points stay `serialize`/`deserializeComponentState`. The prose ladder and every version constant stay in `component_state_io.h`, their one home.
 - `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.
@@ -276,7 +278,7 @@ anything for a trigger shape.
 
 - `editor_geometry` (`core/instrument/ui`) — the shared geometry VOCABULARY every instrument UI module speaks: the `core::ui::Rect` alias, `contains()`, and `OverlayArea` (a one-field `Rect` wrapper, no implicit conversion from `Rect`). Header-only (an INTERFACE CMake target), so it carries no layout of its own.
 - `sample_bands` — **THE band-stack allocator**, and the only module that owns the Sample face's vertical inventory — including `kEditorMinWidth`/`kEditorMinHeight`, the editor's client-area floor, which IS its default size (the shell's `checkSizeConstraint` and opening `ViewRect` both read it; the face grows, never shrinks below what the stack is laid out for). Three bands top-to-bottom (CHROME toolbar+control row / WAVEFORM elastic, floored at two stacked lanes / DECKS bottom-anchored at the knob deck's own wrapped height), plus the waveform band's lane split (`waveformLanes` takes a resolved `LaneSplit`, not a raw bool — only `waveformSurface` folds the source-channel-count decision in). A shared READ-ONLY surface for every band owner — a band's interior module lays out inside the rect it is handed and never re-allocates the stack.
-- `sample_chrome` — the CHROME band's interior: the toolbar row (title + the whole right-anchored control run — preview, velocity knob cell, curve button, channel toggle, Browse) over the strip row, which the piano strip owns outright. The title takes what the run leaves; the strip takes its whole row, inset only by the shared band pad so it lines up with the waveform band beneath.
+- `sample_chrome` — the CHROME band's interior: the toolbar row (title + the whole right-anchored control run — preview, velocity knob cell, channel toggle, Browse) over the strip row, which the piano strip owns outright. The title takes what the run leaves; the strip takes its whole row, inset only by the shared band pad so it lines up with the waveform band beneath. Also `previewGlyph`, the preview button's play triangle — three vertices for one filled-triangle draw, so the button's label needs no font metric and no image asset.
 - `keyboard_strip` — piano-keyboard strip: true white/black key geometry (whites tiled at one width, blacks overlaid at one width and height, straddling their boundary), hit-test resolving black-over-white by zone, root-marker rect, the absolute-position drag resolver, and MIDI note naming under the C4 convention. **Same-class keys are one integer width by construction; the residue of an indivisible band width (`w % 75`, up to 74 px) lands in symmetric end margins, never in a key** — uniform widths and gap-free edge-to-edge tiling cannot both hold, and uniformity wins.
 - `waveform_view` — the WAVEFORM band's interior: `waveformSurface` resolves the drawn lane(s) (two stacked lanes, L over R, only when the mode is stereo AND the source has a second channel — a mono source under stereo mode is dual-mono and draws one lane) plus **the** overlay area, and `laneEnvelope` splits one multi-channel envelope pass per lane. Also maps frame span linearly across a rect; generic named draggable markers with drag-delta resolver, clamp, and zero-crossing snap, plus `markerHandleRect` — a top-strip grab tab distinct from a marker's full-height column, so two markers that share a frame stay independently grabbable (the column goes to the first in draw order; the tab, asked first, resolves the other).
   - **Overlay contract (consumed by later waveform work).** `WaveformSurface::overlay` — equivalently the standalone `waveformOverlayArea(band)` — is the FULL band in both modes. Everything riding the waveform (the amp-envelope trace and its node handles, the start/loop markers, the loop region) draws ONCE into it, spanning both stacked lanes; hit-testing resolves against the same area so a grab in the lower lane reaches them. Anything drawn or hit-tested per lane is a duplicate and a defect — structurally enforced: `overlay` is the distinct `OverlayArea` type (`editor_geometry`), not `Rect`, so every overlay-consuming API (`frameToX`/`markerAtPoint`/`resolveDragFrame`, `envelope_edit`'s `nodeAtPoint`/`resolveNodeDrag`, `envelope_overlay`'s `buildEnvelopePolyline`) rejects a lane rect at compile time rather than silently accepting one.
@@ -285,7 +287,7 @@ anything for a trigger shape.
 - `param_slider` — parameter control-panel: vertical stack of TOGGLE (two-segment selector) and SLIDER (horizontal track) rows; maps normalized value to/from handle pixel.
 - `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.
-- `deck_groups` — also home to `isLiveDeckParam` and `liveCommitFor`, the editor's whole commit-tier routing decision (see "Live parameter delivery" above), and to `OverlayEnv` + `nextOverlaySelection`/`overlayEnvInert`, the whole overlay-selection state machine (exclusivity, the none resting state, and which selections a disabled group makes inert); WHICH groups the Sample face's deck carries, split from `knob_deck`'s HOW they lay out: the `DeckParam` control-id space (the editor's `ParamControl` is an alias of it), the `DeckGroupId` list, `sampleDeckGroups` in signal-flow order (**pitch → filter → amp**, then voice/master), and the deck's bipolar-knob law. Reads `PlayMode` for the AMP group's Gate/Trigger face, which is why this and not `knob_deck` is the module that touches the engine's value layer.
+- `deck_groups` — also home to `isLiveDeckParam` and `liveCommitFor`, the editor's whole commit-tier routing decision (see "Live parameter delivery" above), and to `OverlayEnv` + `nextOverlaySelection`/`overlayEnvInert`, the whole overlay-selection state machine (exclusivity, the none resting state, and which selections a disabled group makes inert); WHICH groups the Sample face's deck carries, split from `knob_deck`'s HOW they lay out: the `DeckParam` control-id space (the editor's `ParamControl` is an alias of it), the `DeckGroupId` list, `sampleDeckGroups` in signal-flow order (**pitch → filter → amp**, then velocity/voice/master), and the deck's bipolar-knob law. Reads `PlayMode` for the AMP group's Gate/Trigger face, which is why this and not `knob_deck` is the module that touches the engine's value layer. Also home to `CurveTarget` + `curveTargetFor` — the VELOCITY group's three cells are popup openers, not dials, and that predicate is the ONE place they are named, so paint, hit-test routing and the popup's title all agree. MASTER is reserved for post-voice-mixer concerns, which is why the curves sit in their own group immediately left of VOICE rather than there.
 - `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.
 - `envelope_overlay` — pure staged-envelope→polyline geometry for the Sample-view overlay (read from `envelope_overlay.h`): maps a `StageEnvelope` to a polyline inside a rect under whichever of TWO layout policies its `EnvKind` selects — an AHDSR draws a bounded param-domain schematic with its release RIGHT-ANCHORED to the canvas edge, an AHD draws 1:1 over the waveform's own time axis — plus a round mid-segment knot on every sloped stage that has a duration. Every vertex clamped in-canvas. Shares the `EnvNode`/`StageEnvelope`/`timeToX`/`levelToY` vocabulary with `envelope_edit` so the drawn handle and its grab region agree pixel-for-pixel. No VST3/REAPER/LICE types at the boundary.
 - `envelope_edit` — pure node hit-test + pixel-delta→clamped-param inverse map for the draggable envelope nodes and their curve knots (read from `envelope_edit.h`): `nodeAtPoint` resolves a grab to the nearest node within a pick radius (Chebyshev distance, draw-order tie-break, knots appended last so a coincident endpoint handle wins); `resolveNodeDrag` maps a pixel delta since grab to a new `StageEnvelope` under the same caller-supplied per-param clamp bounds the knobs use — a drag can never produce a param a knob couldn't. Mirror of `card_drag`/`waveform_view`; the inverse of `envelope_overlay`'s params→polyline forward map, so node-drag, knot-drag and knob-edit read/write one shared model and can never diverge.