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/ui/envelope_edit.h

@@ -51,15 +51,18 @@ NodeHit nodeAtPoint(const StageEnvelope& env, const OverlayArea& area, double to
 // Resolves a drag of `node` to a new StageEnvelope. `grabEnv` is the envelope as of grab time
 // (the shell snapshots it on button-down so the delta is absolute, not accumulated);
 // `dxPixels`/`dyPixels` is the pixel delta since grab.
-//   * X delta -> the node's time param, at the same scale the forward map drew it, clamped to
-//     [0, per-param max].
+//   * X delta -> the node's time param, through the same map the forward draw used — the tapered
+//     slot on an AHDSR, 1:1 wall clock on an AHD — clamped to [0, per-param max].
 //   * Y delta -> the level param (AHDSR DecayEnd's sustain) or, on a knot, the segment's curve
 //     exponent. Ignored for time-only nodes.
+//   * `mods` carries the shared interaction law (param_taper.h): Ctrl scales the pixel delta,
+//     Shift snaps the resolved param to a whole unit of its own category before the clamp. The
+//     shell RE-ANCHORS on every modifier transition, so `mods` is constant across one delta.
 //   * A non-draggable node, an other-kind node, a zero-size area, or totalSeconds <= 0 returns
 //     `grabEnv` unchanged.
 // Only the dragged node's param(s) change. Pure.
 StageEnvelope resolveNodeDrag(const StageEnvelope& grabEnv, EnvNode node, const OverlayArea& area,
                               double totalSeconds, const EnvClampBounds& bounds,
-                              int dxPixels, int dyPixels);
+                              int dxPixels, int dyPixels, const DragModifiers& mods = {});
 
 }  // namespace reasampler::instrument::ui