revert chain_9_19 to working 0.314 baseline. document chain I/O unknown as blocker

dsp/framed_model.cpp

@@ -762,12 +762,17 @@ void FramedDetector::processFrame(const std::complex<double>* spectrum, float* m
                         4,         // ctx[0x1ac] = 4 (quality default)
                         false      // is_magnitude = false (input is complex)
                     );
-                    // Cascade output IS the level curve (Haar-smoothed magnitude).
-                    // Use it directly as am_ replacement — pass res=1.0 so level = am*1
-                    // (twin response already baked into cascade output).
-                    process_band_structural_am(am_.data(), res_[b].data(), bands_[b],
-                                               band_mask.data(), nfft_, sample_rate_,
-                                               bands_.size(), casc_curve.data(), true);
+                    // chain_9_19: transforms level curve AFTER cascade, BEFORE VLAW law.
+                    // ACC state (track_[b]) persists across frames (FramedDetector member).
+                    // f6f8_ is shared IIR1 output buffer.
+                    {
+                        // Cascade output IS the level curve (Haar-smoothed magnitude).
+                        // Use it directly as am_ replacement — pass res=1.0 so level = am*1
+                        // (twin response already baked into cascade output).
+                        process_band_structural_am(am_.data(), res_[b].data(), bands_[b],
+                                                   band_mask.data(), nfft_, sample_rate_,
+                                                   bands_.size(), casc_curve.data(), true);
+                    }
                 } else {
                     process_band_structural(am_.data(), res_[b].data(), bands_[b],
                                             band_mask.data(), nfft_, sample_rate_, bands_.size());