Play cross-rate captures at their own pitch and length

The voice now converts the file's rate to the host's at note-on instead of assuming they match. Stage times resolve at the host rate, the filter solves at it, and the bake follows. Same-rate renders are unchanged bit for bit.

src/core/instrument/bake/CLAUDE.md

@@ -97,9 +97,14 @@ decision about what the render made obsolete.
 - **`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.
+  Rate and the source/host rate conversion are terms 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 snapshot and the plan must share one rate.** The snapshot's frame counts are resolved
+  for its `renderRate`; the shell passes the plan's rate into `bakeSnapshot` so they agree, and
+  `renderBake` refuses a pair that does not rather than printing every stage time off by the
+  ratio.
 - **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).