Bake window: derive it from the rate the voice actually reads at, so a dialled Rate or downward Pitch no longer truncates the file

src/core/instrument/bake/bake_plan.h

@@ -32,7 +32,8 @@ bool bakeWindowNeedsHold(const SampleData& dialed);
 // the bake renders at, which is what the engine's frame counts are consumed against):
 //
 //   Trigger      — the note IS the play span (note-off is ignored anyway), stretched by the
-//                  deepest downward Varispeed offset.
+//                  slowest read the dialed voice can reach: Rate under BOTH engines, plus the
+//                  deepest downward pitch offset under Varispeed.
 //   Gate, loop   — `hold` is the note length; the end offset is the release.
 //   Gate, no loop— the read head runs off the source and frees the voice whatever the gate is
 //                  doing, so the note is the whole post-start span, stretched the same way.
@@ -44,7 +45,7 @@ bool bakeWindowNeedsHold(const SampleData& dialed);
 // Every case is padded by the voice's terminal declick ramp (kDeclickFrames): trailing
 // silence is free, and closing the window on the frame the ramp starts is a hard cut.
 // `hold` is read only in the Gate-with-loop case; `velocity` is the velocity the note fires
-// at, and it feeds the Varispeed stretch as well as the render.
+// at, and it feeds the Varispeed half of that stretch as well as the render.
 //
 // Takes no tempo: nothing derived here is beat-denominated. The one field that is — `hold` —
 // meets the tempo in resolveNote, with the rest of the program's beat-denominated fields.