fix: harden note-program model against corrupt tempo/division/denomination records

Reject subnormal BPM that overflows to NaN, normalize Division equality, pin a single out-of-range-denomination interpretation across all readers, flag collapsed capture windows, add offset off-view editors and structural static_asserts, collapse duplicated CLAUDE.md facts.

src/core/instrument/note/note_program.h

@@ -1,12 +1,12 @@
 // note_program — the programmed capture signal: one note length, one velocity, two anchored
 // offsets, and the one resolver a preview and a bake must share.
 //
-// Resolved times are rate-free SECONDS relative to note-on; the caller converts against the
-// live sample rate.
+// Resolved times are rate-free seconds (this directory's CLAUDE.md: the standing ruling).
 
 #pragma once
 
 #include <cstdint>
+#include <type_traits>
 
 #include "core/instrument/note/musical_division.h"
 #include "core/instrument/note/tempo.h"
@@ -52,6 +52,12 @@ double offsetSeconds(OffsetAmount amount, Tempo tempo);
 // The unit toggle: the same instant restated in the other denomination.
 OffsetAmount redenominate(OffsetAmount amount, Denomination to, Tempo tempo);
 
+// Edit the magnitude via its non-stored view without changing which denomination is stored
+// — a popup's ms and beats fields both stay live no matter which one the offset was entered
+// in; only `redenominate` changes the stored denomination itself.
+OffsetAmount withMsView(OffsetAmount amount, double ms, Tempo tempo);
+OffsetAmount withBeatsView(OffsetAmount amount, double beats, Tempo tempo);
+
 // Two types rather than one carrying an anchor field: the anchor is then unswappable at
 // compile time. Sign is uniform — positive is later in time — so a capture that opens before
 // the note is a negative start offset, and a negative end offset truncates before release.
@@ -75,6 +81,11 @@ private:
     OffsetAmount amount_{};
 };
 
+static_assert(!std::is_constructible_v<StartOffset, EndOffset>,
+              "StartOffset and EndOffset must not be interchangeable at compile time");
+static_assert(!std::is_convertible_v<OffsetAmount, StartOffset>,
+              "the anchor constructor must stay explicit");
+
 struct NoteProgram {
     Division length{};
     StartOffset start{};
@@ -89,7 +100,10 @@ struct ResolvedNote {
     double noteOffSeconds = 0.0;       // == the note's sounding length, note-on being 0
     double captureStartSeconds = 0.0;  // negative when the capture opens before the note
     double captureEndSeconds = 0.0;
-    std::uint8_t velocity = 1;
+    std::uint8_t velocity = 100;  // resolveNote always overwrites this; matches Velocity's own default
+    // True when the programmed end offset inverted the window and resolveNote collapsed it
+    // to zero length instead — lets a popup explain an empty window rather than just show one.
+    bool windowCollapsed = false;
 
     double captureLengthSeconds() const { return captureEndSeconds - captureStartSeconds; }
 };