Docs: record cross-rate playback; finish SEPT_VERIFY sample-rate checks

docs/COMPLETED.md

@@ -1811,3 +1811,25 @@ Windows window class, so side-by-side installs could run the wrong channel's cod
 each channel now registers its own class. Mechanism detail: `src/core/ui/CLAUDE.md`
 (`window_origin`) and `src/shell/actions/drag_out_win.h`. Not DAW-verified — checks
 are tracked in `docs/SEPT_VERIFY.md` §4.
+
+### Cross-rate playback: ReaSampler 9000 plays any file rate at its own pitch and length
+
+ReaSampler 9000 now plays a sample whose file rate differs from the project rate at its
+correct pitch and wall-clock length — previously, e.g., a 44.1 kHz file in a 48 kHz project
+played about 1.47 semitones sharp and short. The fix folds a file-rate/host-rate factor
+into the read once per note rather than resampling at load; envelope stage times, the
+filter, the loop crossfade, the Preserve (time-stretch) engine, and the bake all follow the
+same factor (`SampleData::sourceRateRatio`, `play_params.h`; mechanism detail lives in
+`src/core/instrument/CLAUDE.md`'s "Two frame domains" section, not restated here).
+Same-rate playback at Rate 100% is unchanged, pinned by hashes of pre-change renders.
+
+Landed in the same merge: a Preserve splice-crossfade fix that also changes output at
+matched rate for high Rate settings (~200%+) — a down-splice previously read audio a prior
+splice had already overwritten; Daniel approved the change. A file more than 32x the
+project rate (`kMaxSourceRateRatio`, `play_params.h`) is refused: the ReaSampler 9000
+editor title shows "... -- <refusal text>, not played" (clearing once another sample loads
+or the project rate makes it supported), and a bake refuses with "cannot render: ...". A
+project sample-rate change while the plugin is inactive re-stamps in place rather than
+reloading from disk.
+
+Not DAW-verified — checks are tracked in `docs/SEPT_VERIFY.md` §6.