Close derived-bake-window review findings: NaN-guard remaining wire doubles, pin Trigger-span agreement, retire dead quantizer

Guards params_payload.cpp's filter-tail seconds and both keyTrack sites against NaN; pins Voice::start's Trigger-span formula against trigger_seam; retires unused shortestDivisionAtLeast.

tests/test_note_program.cpp

@@ -219,8 +219,10 @@ static void testAnExactLengthCarriesDurationsPastTheLaddersTopRung() {
     const Tempo t = at(120.0);
     const double pastTheLadder = t.beatsToSeconds(kMaxDivisionBeats) * 3.0;
     CHECK(almostEqual(noteLengthSeconds(lengthOfSeconds(pastTheLadder), t), pastTheLadder));
-    // …and the ladder really does saturate there, which is what makes the seam load-bearing.
-    CHECK(almostEqual(divisionBeats(shortestDivisionAtLeast(kMaxDivisionBeats * 3.0)),
+    // …and the ladder really does saturate there, which is what makes the seam load-bearing:
+    // its longest rung (the dotted top) IS kMaxDivisionBeats, so nothing on it reaches
+    // pastTheLadder.
+    CHECK(almostEqual(divisionBeats(makeDivision(kMaxQuarterExponent, DivisionModifier::Dotted)),
                       kMaxDivisionBeats));
 }