instrument: latch the note done at the read-head run-off, fit the migrated fades, and lift the curve dial and overlay selection into pure modules

src/core/instrument/ui/deck_groups.h

@@ -133,6 +133,25 @@ enum class LiveDragKind { kOther, kDeckKnob, kEnvNode };
 // can reach — AHDSR or AHD, on any of the three envelopes — is itself live.
 bool liveCommitFor(LiveDragKind kind, int paramId);
 
+// Which envelope the waveform overlay draws and edits. Exclusive across the three envelope
+// decks, and kNone is a valid resting state — the editor opens there. Transient view state:
+// never persisted, never a parameter.
+enum class OverlayEnv { kNone, kAmp, kPitch, kFilter };
+
+// The envelope a deck's overlay-select radio picks; kNone for any other control id.
+OverlayEnv overlayEnvForRadio(int radioId);
+
+// The selection a click on `radioId` produces from `current`. Two rules, provable here rather
+// than in the shell: picking another deck's radio switches to it (exclusivity), and clicking
+// the ACTIVE one clears back to kNone — "no envelope shown" is a state the user can get back
+// to, not an error. A non-radio id leaves the selection alone.
+OverlayEnv nextOverlaySelection(OverlayEnv current, int radioId);
+
+// Whether the overlay for `env` is INERT: its deck group's enable toggle is off, so its knobs
+// are drawn-but-dead and a node drag on the same params must be too — otherwise a drag reaches
+// a param a knob couldn't (envelope_edit.h). Amp has no enable toggle and is never inert.
+bool overlayEnvInert(OverlayEnv env, bool pitchEnvEnabled, bool filterEnabled);
+
 // The deck's BIPOLAR knob law: 0.5 of the knob's travel is zero depth, the ends are -1 and
 // +1. Exact inverses, and exact at the centre detent (0.5 -> 0 -> 0.5), so a knob parked at
 // centre can never persist a hair of modulation. Out-of-range norm clamps to the endpoints.