One taper, one modifier law: extract param_taper, raise the stage ceiling to 10 s, and make the AHDSR schematic axis the taper itself

src/core/instrument/CLAUDE.md

@@ -312,15 +312,20 @@ anything for a trigger shape.
   - **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.
 - `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.
-- `param_slider` — parameter control-panel: vertical stack of TOGGLE (two-segment selector) and SLIDER (horizontal track) rows; maps normalized value to/from handle pixel.
+- `param_taper` — THE norm↔value tapers every variable control shares, and the modifier vocabulary its drag surfaces read: the stage-time shifted-log (and `kStageTimeMaxSeconds`, the ONE home of the stage-time ceiling that `envelope_overlay`'s `kGateStageMaxSeconds` and `deck_values`' `kEnvTimeMaxSeconds` alias), the centre-expanded semitone-depth map, `DragModifiers`/`kFineDragScale`/`fineDrag`, the `UnitCategory` axis, and the four whole-unit snaps Shift applies. Extracted from `deck_values` because it has THREE consumers in two dependency layers — the knob's needle (`deck_values`), the AHDSR schematic axis and its drag inverse (`envelope_overlay`/`envelope_edit`, which sit *below* `deck_values`), and the VST3 host's `toPlain`/`toNormalized`. **Three functions that agree today is a defect, not an implementation choice**; solving the include edge by copying the map is the specific mistake this exists to prevent. Both maps resolve their output onto a fixed decimal quantum, which is what makes "every default has an EXACT normalized preimage" a structural guarantee rather than a libm coincidence — the header states the argument; the converse round trip at an arbitrary norm is explicitly NOT required.
+- `param_slider` — parameter control-panel: vertical stack of TOGGLE (two-segment selector) and SLIDER (horizontal track) rows; maps normalized value to/from handle pixel. `knobDragValue` is the knob's grab-anchored absolute drag law and applies Ctrl's rate — but not Shift's snap, whose whole unit is a property of the control's unit category this module does not know.
 - `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. Carries a SECOND hit-test, `hitTestKnobFace`, resolved against the drawn CIRCLES rather than the cell: a double-click reset is aimed at a dial, so the label band and the cell margins must miss where a drag grab deliberately does not, and only a radial resolve can tell the inner curve dial from the outer ring it sits inside. **The cell/knob/label sizes and `sample_bands`' editor floor move as a pair** — wider cells need a wider floor width or the deck wraps to a fourth row. A group carries TWO caption-toggle slots, laid right-to-left: the second exists because a group whose knob row is wider than its caption row has caption slack a toggle can occupy for free, and the deck has fourteen pixels of headroom on its first row at the editor's floor width — a `rowToggle` would widen the GROUP and wrap the deck to a fourth row, past what the minimum window holds. **A group's cell run is a RESERVED WIDTH, not a fixed cell size**: a `-1` id reserves one cell's width without a cell, and the cells present divide the whole run between them at one uniform integer width (residue in symmetric end margins). That is what lets a mode flip drop controls from a face — Trigger's AMP and FILTER ENV lose their Sustain/Release stages — without either reflowing the deck or leaving dead slots in the box; a face with fewer controls simply gets roomier cells. Do not reintroduce fixed-width cells with blank slots.
 - `deck_values` — the deck's control-id ↔ parameter-set BINDING and its display units, split
   from the editor shell on the same axis `deck_groups` was split from `knob_deck`: `deck_groups`
   says which controls exist, this says what each one's value MEANS. Holds `deckParamNorm` /
-  `setDeckParam` (the normalized ↔ stored-seconds/fraction/position maps and their clamps),
-  `resetDeckParam` (the double-click reset — the defaults are READ off a default-constructed
-  `PlaySeconds`, so there is no second table of defaults to drift), and `formatEnvTimeMs`, the
+  `setDeckParam` (the normalized ↔ stored-seconds/fraction/position binding and its clamps, over
+  `param_taper`'s maps), `resetDeckParam` (the double-click reset — the defaults are READ off a
+  default-constructed `PlaySeconds`, so there is no second table of defaults to drift, and the
+  value is COPIED rather than round-tripped: that taper bypass is mandatory and must never be
+  "simplified" back into a norm round trip), `deckParamUnit`/`snapDeckParamNorm` (THE snap-unit
+  table, and where each control's full scale enters — a whole DISPLAYED percent is a different
+  norm step at 0..100 %, 0..200 % and ±100 %), and `formatEnvTimeMs`, the
   ONE time-constant formatter: every displayed time constant reads in **ms**, never seconds, so
   two stage times are comparable at a glance. A display-unit decision only — nothing about the
   stored representation changes. Links the header-only `play_seconds`, deliberately not
@@ -336,7 +341,7 @@ anything for a trigger shape.
 
 ## Gotchas
 
-- **An AHDSR's overlay x-axis is schematic, not PCM-aligned** — it does NOT line up with the waveform under it; only a sustain-less AHD's x-axis is wall-clock/PCM-aligned. Don't assume a gated envelope's curve is time-accurate against the sample.
+- **An AHDSR's overlay x-axis is schematic, not PCM-aligned, and it is not linear in seconds either** — it does NOT line up with the waveform under it, and each of its four equal stage slots is filled by `param_taper`'s own norm, so a node's position within its slot IS its knob's needle position. Two stages therefore cannot be compared by eye at a 10:1 ratio; the ms labels carry the number. Only a sustain-less AHD's x-axis is wall-clock/PCM-aligned and linear. Content-fit auto-scale and a minimum drawn stage width were both considered and REJECTED — the first moves the axis under the hand, the second decouples the drawn position from the value and breaks the drag inverse.
 - **An AHD's Hold is a FRACTION of what attack and decay left, never a time.** That is the whole reason A+H+D ≤ span holds by construction; adding a clamp on the sum, or re-expressing Hold as a duration, reintroduces the overflow the fraction exists to prevent.
 - **`param_slider`'s linear slider rows are retired on the parameter surface** — per root `CLAUDE.md`'s FB2 note, the `Knob` primitive (the knob-deck grammar) is now the only live consumer of that half of `param_slider`. Don't assume `param_slider`'s SLIDER row type is still drawn.
 - **The engine's per-sample path is inline ON PURPOSE.** `Voice::advanceFrame` and the three evaluators in `envelopes.h` live in headers so `VoiceEngine::render`'s inner loop — in another TU, with no LTO configured — still inlines the whole stack. Moving either out of line, or giving the evaluators a virtual `tick()`, puts a call on the hottest loop in the program.