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/CLAUDE.md

@@ -67,10 +67,12 @@ decision about what the render made obsolete.
 - **`BakePlan` speaks two frame domains** — the captured file's and the render's, which are
   offset from each other whenever the note and the capture window do not start together.
   `bake_plan.h` says which field is in which; do not read them as one clock.
-- **`defaultBakeProgram`'s Varispeed bound is an upper bound, not a model.** A downward pitch
-  offset makes the read head take longer to cross its span, so the window is scaled by the
-  deepest downward offset the voice can reach — a shallower excursion leaves trailing silence
-  in the file. Both the Trigger span and the Gate exhaustion length take it.
+- **`defaultBakeProgram`'s read-rate bound is an upper bound, not a model.** Anything that
+  slows the read makes the head take longer to cross its span, so the window is scaled by the
+  slowest read the voice can reach — a shallower excursion leaves trailing silence in the file.
+  Rate is a term of it under BOTH engines and the deepest downward pitch offset under Varispeed
+  alone (`playbackStretch` argues each); both the Trigger span and the Gate exhaustion length
+  take the product, and the Gate-with-loop branch takes neither.
 - **The bake fires at the instance's PREVIEW velocity, not a constant.** Three velocity curves
   are live, so the velocity is a property of the sound being printed and not a detail of the
   render; it also feeds the Varispeed bound above (a velocity→pitch curve moves the window).