diff --git a/PLAN.md b/PLAN.md
index 4cc64a1..4fedb21 100644
--- a/PLAN.md
+++ b/PLAN.md
@@ -233,6 +233,23 @@ downsampling) guarantee the contract numerically — the envelope can
 misbehave and the contract still holds. Never bypassed, never
 disabled.
 
+**Contract scope (caveat).** The ≤ −0.1 dBTP guarantee holds at the
+*filter's output*, not at the speaker. The bus filter is hardcoded
+F32 stereo @ 48 kHz (`headroom-dsp::limiter`'s 4× oversampler is
+sized for 48 k); when the real sink negotiates a different rate
+(44.1 kHz, 96 kHz, 192 kHz), PipeWire inserts a downstream
+resampler between `filter.playback` and the sink. Polynomial /
+windowed-sinc resamplers can elevate inter-sample peaks slightly
+through their own reconstruction, so the limiter's true-peak
+guarantee leaks across that resampling stage. In practice the
+elevation is small (a few tenths of a dB worst case for a clean
+band-limited resampler), and the contract still holds at the bus
+output where headroom is in control. **For the contract to hold
+end-to-end the filter would need to match the real sink's rate
+and rebuild its DSP coefficients on rate-change** — that's the
+v1 work tracked as PLAN §11 "filter rate matching" (deferred from
+8d, gated on a multi-rate hardware test bench).
+
 **Soft tier — the comfort cap.** Targets a *dynamic* ceiling computed
 as `program_lufs + max_psr_db`. Smooth attack/release envelope so the
 gain reduction sounds like volume riding, not a slap. Pulls transients
@@ -903,6 +920,14 @@ lost. Pick up by name when the trigger that gates them fires.
   for simplicity. Revisit if real users ask for it; the store-level
   change is a flag on the setter methods. **Dormant** — no user has
   asked through Phase 8.
+- **Filter rate matching to the real sink.** *(F5 follow-up.)* §3.1
+  documents the contract leak when the real sink runs at a
+  non-48 kHz native rate. Closing it requires dynamic
+  `FILTER_SAMPLE_RATE`, kernel rebuild on real-sink change
+  (compressor + limiter coefficients are rate-dependent), and
+  Layer A's `LAYER_A_BLOCK_DT_S` constant becoming dynamic too.
+  Gated on a multi-rate hardware test bench — no point shipping
+  the refactor without something to validate it against. **v1 scope.**
 - ~~**Filter playback BUSY spikes (periodic, ~10 s cadence).**~~
   **Closed in 8e (`d52cd6d`).** The instrumentation added by 8e
   did not reproduce the ~8×-baseline outlier pattern in a ~3 min